Functions

Scalar Functions

Scalar functions return one result for each row.

Mathematical Functions

ABS

ABS(expr)

Description: The absolute value of a specific field.

Return value type: Same as the field being used

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

ACOS

ACOS(expr)

Description: The arc cosine of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

ASIN

ASIN(expr)

Description: The arc sine of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

ATAN

ATAN(expr)

Description: The arc tangent of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

CEIL

CEIL(expr)

Description: The rounded up value of a specific field

Return value type: Same as the field being used

Applicable data types: Numeric

Applicable table types: standard tables and supertables

Nested query: It can be used in both the outer query and inner query in a nested query.

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

COS

COS(expr)

Description: The cosine of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

FLOOR

FLOOR(expr)

Description: The rounded down value of a specific field More explanations: The restrictions are same as those of the CEIL function.

LOG

LOG(expr [, base])

Description: The logarithm of a specific field with base as the radix. If you do not enter a base, the natural logarithm of the field is returned.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

POW

POW(expr, power)

Description: The power of a specific field with power as the exponent.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

ROUND

ROUND(expr)

Description: The rounded value of a specific field. More explanations: The restrictions are same as those of the CEIL function.

SIN

SIN(expr)

Description: The sine of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

SQRT

SQRT(expr)

Description: The square root of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

TAN

TAN(expr)

Description: The tangent of a specific field.

Return value type: Double

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Usage: This function can only be used on data columns. It can be used with selection and projection functions but not with aggregation functions.

Concatenation Functions

Concatenation functions take strings as input and produce string or numeric values as output.

CHAR_LENGTH

CHAR_LENGTH(expr)

Description: The length in number of characters of a string

Return value type: Bigint

Applicable data types: VARCHAR and NCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

CONCAT

CONCAT(expr1, expr2 [, expr] ...)

Description: The concatenation result of two or more strings

Return value type: If the concatenated strings are VARCHARs, the result is a VARCHAR. If the concatenated strings are NCHARs, the result is an NCHAR. If an input value is null, the result is null.

Applicable data types: VARCHAR and NCHAR You can concatenate between 2 and 8 strings.

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

CONCAT_WS

CONCAT_WS(separator_expr, expr1, expr2 [, expr] ...)

Description: The concatenation result of two or more strings with separator

Return value type: If the concatenated strings are VARCHARs, the result is a VARCHAR. If the concatenated strings are NCHARs, the result is an NCHAR. If an input value is null, the result is null.

Applicable data types: VARCHAR and NCHAR You can concatenate between 3 and 9 strings.

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

LENGTH

LENGTH(expr)

Description: The length in bytes

Return value type: Bigint

Applicable data types: VARCHAR and NCHAR and VARBINARY

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

LOWER

LOWER(expr)

Description: Convert the input string to lower case

Return value type: Same as input

Applicable data types: VARCHAR and NCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

LTRIM

LTRIM(expr)

Description: Remove the left leading blanks of a string

Return value type: Same as input

Applicable data types: VARCHAR and NCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

RTRIM

LTRIM(expr)

Description: Remove the right tailing blanks of a string

Return value type: Same as input

Applicable data types: VARCHAR and NCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

SUBSTR

SUBSTR(expr, pos [, len])

Description: The sub-string starting from pos with length of len from the original string str - If len is not specified, it means from pos to the end.

Return value type: Same as input

Applicable data types: VARCHAR and NCHAR Parameter pos can be an positive or negative integer; If it's positive, the starting position will be counted from the beginning of the string; if it's negative, the starting position will be counted from the end of the string.

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: table, STable

UPPER

UPPER(expr)

Description: Convert the input string to upper case

Return value type: Same as input

Applicable data types: VARCHAR and NCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: table, STable

Conversion Functions

Conversion functions change the data type of a value.

CAST

CAST(expr AS type_name)

Description: Convert the input data expr into the type specified by type_name. This function can be used only in SELECT statements.

Return value type: The type specified by parameter type_name

Applicable data types: All data types except JSON and VARBINARY. If type_name is VARBINARY, expr can only be VARCHAR.

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

More explanations:

• Error will be reported for unsupported type casting
• Some values of some supported data types may not be casted, below are known issues:
  1. Some strings cannot be converted to numeric values. For example, the string a may be converted to 0. However, this does not produce an error.
  2. If a converted numeric value is larger than the maximum size for the specified type, an overflow will occur. However, this does not produce an error.
  3. If a converted string value is larger than the maximum size for the specified type, the output value will be truncated. However, this does not produce an error.

TO_ISO8601

TO_ISO8601(expr [, timezone])

Description: The ISO8601 date/time format converted from a UNIX timestamp, plus the timezone. You can specify any time zone with the timezone parameter. If you do not enter this parameter, the time zone on the client is used.

Return value type: VARCHAR

Applicable data types: Integers and timestamps

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

More explanations:

• You can specify a time zone in the following format: [z/Z, +/-hhmm, +/-hh, +/-hh:mm]. For example, TO_ISO8601(1, "+00:00").
• If the input is a UNIX timestamp, the precision of the returned value is determined by the digits of the input timestamp
• If the input is a column of TIMESTAMP type, the precision of the returned value is same as the precision set for the current data base in use

TO_JSON

TO_JSON(str_literal)

Description: Converts a string into JSON.

Return value type: JSON

Applicable data types: JSON strings in the form {"literal": literal}. {} indicates a null value. The key must be a string literal. The value can be a numeric literal, string literal, Boolean literal, or null literal. str_literal cannot include escape characters.

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: table, STable

TO_UNIXTIMESTAMP

TO_UNIXTIMESTAMP(expr [, return_timestamp])

return_timestamp: {
    0
  | 1
}

Description: UNIX timestamp converted from a string of date/time format

Return value type: BIGINT, TIMESTAMP

Applicable column types: VARCHAR and NCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

More explanations:

• The input string must be compatible with ISO8601/RFC3339 standard, NULL will be returned if the string can't be converted
• The precision of the returned timestamp is same as the precision set for the current data base in use
• return_timestamp indicates whether the returned value type is TIMESTAMP or not. If this parameter set to 1, function will return TIMESTAMP type. Otherwise function will return BIGINT type. If parameter is omitted, default return value type is BIGINT.

TO_CHAR

TO_CHAR(ts, format_str_literal)

Description: Convert a ts column to string as the format specified

Version: Since ver-3.2.2.0

Return value type: VARCHAR

Applicable column types: TIMESTAMP

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Supported Formats

Format	Comment	example
AM,am,PM,pm	Meridiem indicator(without periods)	07:00:00am
A.M.,a.m.,P.M.,p.m.	Meridiem indicator(with periods)	07:00:00a.m.
YYYY,yyyy	year, 4 or more digits	2023-10-10
YYY,yyy	year, last 3 digits	023-10-10
YY,yy	year, last 2 digits	23-10-10
Y,y	year, last digit	3-10-10
MONTH	full uppercase of month	2023-JANUARY-01
Month	full capitalized month	2023-January-01
month	full lowercase of month	2023-january-01
MON	abbreviated uppercase of month(3 char)	JAN, SEP
Mon	abbreviated capitalized month	Jan, Sep
mon	abbreviated lowercase of month	jan, sep
MM,mm	month number 01-12	2023-01-01
DD,dd	month day, 01-31
DAY	full uppercase of week day	MONDAY
Day	full capitalized week day	Monday
day	full lowercase of week day	monday
DY	abbreviated uppercase of week day	MON
Dy	abbreviated capitalized week day	Mon
dy	abbreviated lowercase of week day	mon
DDD	year day, 001-366
D,d	week day number, 1-7, Sunday(1) to Saturday(7)
HH24,hh24	hour of day, 00-23	2023-01-30 23:59:59
hh12,HH12, hh, HH	hour of day, 01-12	2023-01-30 12:59:59PM
MI,mi	minute, 00-59
SS,ss	second, 00-59
MS,ms	milli second, 000-999
US,us	micro second, 000000-999999
NS,ns	nano second, 000000000-999999999
TZH,tzh	time zone hour	2023-01-30 11:59:59PM +08

More explanations:

• The output format of Month, Day are left aligined, like2023-OCTOBER -01, 2023-SEPTEMBER-01, September is the longest, no paddings. Week days are slimilar.
• When ms,us,ns are used in to_char, like to_char(ts, 'yyyy-mm-dd hh:mi:ss.ms.us.ns'), The time of ms,us,ns corresponds to the same fraction seconds. When ts is 1697182085123, the output of ms is 123, us is 123000, ns is 123000000.
• If we want to output some characters of format without converting, surround it with double quotes. to_char(ts, 'yyyy-mm-dd "is formated by yyyy-mm-dd"'). If want to output double quotes, add a back slash before double quote, like to_char(ts, '\"yyyy-mm-dd\"') will output "2023-10-10".
• For formats that output digits, the uppercase and lowercase formats are the same.
• It's recommended to put time zone in the format, if not, the default time zone will be that in server or client.
• The precision of the input timestamp will be recognized automatically according to the precision of the table used, milliseconds will be used if no table is specified.

TO_TIMESTAMP

TO_TIMESTAMP(ts_str_literal, format_str_literal)

Description: Convert a formated timestamp string to a timestamp

Version: Since ver-3.2.2.0

Return value type: TIMESTAMP

Applicable column types: VARCHAR

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

Supported Formats: The same as TO_CHAR.

More explanations:

• When ms, us, ns are used in to_timestamp, if multi of them are specified, the results are accumulated. For example, to_timestamp('2023-10-10 10:10:10.123.000456.000000789', 'yyyy-mm-dd hh:mi:ss.ms.us.ns') will output the timestamp of 2023-10-10 10:10:10.123456789.
• The uppercase or lowercase of MONTH, MON, DAY, DY and formtas that output digits have same effect when used in to_timestamp, like to_timestamp('2023-JANUARY-01', 'YYYY-month-dd'), month can be replaced by MONTH, or month. The cases are ignored.
• If multi times are specified for one component, the previous will be overwritten. Like to_timestamp('2023-22-10-10', 'yyyy-yy-MM-dd'), the output year will be 2022.
• To avoid unexpected time zone used during the convertion, it's recommended to put time zone in the ts string, e.g. '2023-10-10 10:10:10+08'. If time zone not specified, default will be that in server or client.
• The default timestamp if some components are not specified will be: 1970-01-01 00:00:00 with the timezone specified or default to local timezone. Only DDD is specified without DD is not supported currently, e.g. format 'yyyy-mm-ddd' is not supported, but 'yyyy-mm-dd' is supported.
• If AM or PM is specified in formats, the Hour must between 1-12.
• In some cases, to_timestamp can convert correctly even the format and the timestamp string are not totally matched. Like to_timetamp('200101/2', 'yyyyMM1/dd'), the digit 1 in format string are ignored, and the output timestsamp is 2001-01-02 00:00:00. Spaces and tabs in formats and tiemstamp string are also ignored automatically.
• The precision of the output timestamp will be the same as the table in SELECT stmt, millisecond will be used if no table is specified. The output of select to_timestamp('2023-08-1 10:10:10.123456789', 'yyyy-mm-dd hh:mi:ss.ns') will be truncated to millisecond precision. If a nano precision table is specified, no truncation will be applied. Like select to_timestamp('2023-08-1 10:10:10.123456789', 'yyyy-mm-dd hh:mi:ss.ns') from db_ns.table_ns limit 1.

Time and Date Functions

These functions perform operations on times and dates.

All functions that return the current time, such as NOW, TODAY, and TIMEZONE, are calculated only once per statement even if they appear multiple times.

NOW

NOW()

Description: The current time of the client side system

Return value type: TIMESTAMP

Applicable column types: TIMESTAMP only

Applicable table types: standard tables and supertables

Nested query: It can be used in both the outer query and inner query in a nested query.

More explanations:

• Add and Subtract operation can be performed, for example NOW() + 1s, the time unit can be: b(nanosecond), u(microsecond), a(millisecond)), s(second), m(minute), h(hour), d(day), w(week)
• The precision of the returned timestamp is same as the precision set for the current data base in use

TIMEDIFF

TIMEDIFF(expr1, expr2 [, time_unit])

Description: The difference between two timestamps, and rounded to the time unit specified by time_unit

Return value type: BIGINT

Applicable column types: UNIX-style timestamps in BIGINT and TIMESTAMP format and other timestamps in VARCHAR and NCHAR format

Applicable table types: standard tables and supertables

Nested query: It can be used in both the outer query and inner query in a nested query.

More explanations:

• Time unit specified by time_unit can be: 1b (nanoseconds), 1u (microseconds), 1a (milliseconds), 1s (seconds), 1m (minutes), 1h (hours), 1d (days), or 1w (weeks)
• The precision of the returned timestamp is same as the precision set for the current data base in use
• If the input data is not formatted as a timestamp, the returned value is null.

TIMETRUNCATE

TIMETRUNCATE(expr, time_unit [, use_current_timezone])

use_current_timezone: {
    0
  | 1
}

Description: Truncate the input timestamp with unit specified by time_unit

Return value type: TIMESTAMP

Applicable column types: UNIX-style timestamps in BIGINT and TIMESTAMP format and other timestamps in VARCHAR and NCHAR format

Applicable table types: standard tables and supertables

More explanations:

• Time unit specified by time_unit can be: 1b (nanoseconds), 1u (microseconds), 1a (milliseconds), 1s (seconds), 1m (minutes), 1h (hours), 1d (days), or 1w (weeks)
• The precision of the returned timestamp is same as the precision set for the current data base in use
• If the input data is not formatted as a timestamp, the returned value is null.
• When using 1d/1w as the time unit to truncate timestamp, you can specify whether to truncate based on the current time zone by setting the use_current_timezone parameter. Value 0 indicates truncation using the UTC time zone, value 1 indicates truncation using the current time zone. For example, if the time zone configured by the Client is UTC + 0800, TIMETRUNCATE ('2020-01-01 23:00:00', 1d, 0) returns the result of '2020-01-01 08:00:00'. When using TIMETRUNCATE ('2020-01-01 23:00:00', 1d, 1), the result is 2020-01-01 00:00:00 '. When use_current_timezone is not specified, use_current_timezone defaults to 1.

TIMEZONE

TIMEZONE()

Description: The timezone of the client side system

Applicable data types: VARCHAR

Applicable column types: None

Applicable table types: standard tables and supertables

TODAY

TODAY()

Description: The timestamp of 00:00:00 of the client side system

Return value type: TIMESTAMP

Applicable column types: TIMESTAMP only

Applicable table types: standard tables and supertables

More explanations:

• Add and Subtract operation can be performed, for example TODAY() + 1s, the time unit can be: b(nanosecond), u(microsecond), a(millisecond)), s(second), m(minute), h(hour), d(day), w(week)
• The precision of the returned timestamp is same as the precision set for the current data base in use

Aggregate Functions

Aggregate functions return one row per group. You can use windows or GROUP BY to group data. Otherwise, the entire query is considered a single group.

TDengine supports the following aggregate functions:

APERCENTILE

APERCENTILE(expr, p [, algo_type])

algo_type: {
    "default"
  | "t-digest"
}

Description: Similar to PERCENTILE, but a simulated result is returned

Return value type: DOUBLE

Applicable data types: Numeric

Applicable table types: standard tables and supertables

Explanations:

• p is in range [0,100], when p is 0, the result is same as using function MIN; when p is 100, the result is same as function MAX.
• algo_type can only be input as default or t-digest Enter default to use a histogram-based algorithm. Enter t-digest to use the t-digest algorithm to calculate the approximation of the quantile. default is used by default.
• The approximation result of t-digest algorithm is sensitive to input data order. For example, when querying STable with different input data order there might be minor differences in calculated results.

AVG

AVG(expr)

Description: The average value of the specified fields.

Return value type: DOUBLE

Applicable data types: Numeric

Applicable table types: standard tables and supertables

COUNT

COUNT({* | expr})

Description: The number of records in the specified fields.

Return value type: BIGINT

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• Wildcard (*) is used to represent all columns. If you input a specific column, the number of non-null values in the column is returned.

ELAPSED

ELAPSED(ts_primary_key [, time_unit])

Description: elapsed function can be used to calculate the continuous time length in which there is valid data. If it's used with INTERVAL clause, the returned result is the calculated time length within each time window. If it's used without INTERVAL clause, the returned result is the calculated time length within the specified time range. Please be noted that the return value of elapsed is the number of time_unit in the calculated time length.

Return value type: Double if the input value is not NULL;

Return value type: TIMESTAMP

Applicable tables: table, STable, outer in nested query

Explanations:

• ts_primary_key parameter can only be the first column of a table, i.e. timestamp primary key.
• The minimum value of time_unit is the time precision of the database. If time_unit is not specified, the time precision of the database is used as the default time unit. Time unit specified by time_unit can be: 1b (nanoseconds), 1u (microseconds), 1a (milliseconds), 1s (seconds), 1m (minutes), 1h (hours), 1d (days), or 1w (weeks)
• It can be used with INTERVAL to get the time valid time length of each time window. Please be noted that the return value is same as the time window for all time windows except for the first and the last time window.
• order by asc/desc has no effect on the result.
• group by tbname must be used together when elapsed is used against a STable.
• group by must NOT be used together when elapsed is used against a table or sub table.
• When used in nested query, it's only applicable when the inner query outputs an implicit timestamp column as the primary key. For example, select elapsed(ts) from (select diff(value) from sub1) is legal usage while select elapsed(ts) from (select * from sub1) is not. In addition, because elapsed has a strict dependency on the timeline, a statement like `select elapsed(ts) from (select diff(value) from st group by tbname) will return a meaningless result.
• It can't be used with leastsquares, diff, derivative, top, bottom, last_row, interp.

LEASTSQUARES

LEASTSQUARES(expr, start_val, step_val)

Description: The linear regression function of a specified column, start_val is the initial value and step_val is the step value.

Return value type: A string in the format of "(slope, intercept)"

Applicable data types: Numeric

Applicable table types: table only

SPREAD

SPREAD(expr)

Description: The difference between the max and the min of a specific column

Return value type: DOUBLE

Applicable data types: Integers and timestamps

Applicable table types: standard tables and supertables

STDDEV

STDDEV(expr)

Description: Standard deviation of a specific column in a table or STable

Return value type: DOUBLE

Applicable data types: Numeric

Applicable table types: standard tables and supertables

SUM

SUM(expr)

Description: The sum of a specific column in a table or STable

Return value type: DOUBLE or BIGINT

Applicable data types: Numeric

Applicable table types: standard tables and supertables

HYPERLOGLOG

HYPERLOGLOG(expr)

Description: The cardinal number of a specific column is returned by using hyperloglog algorithm. The benefit of using hyperloglog algorithm is that the memory usage is under control when the data volume is huge. However, when the data volume is very small, the result may be not accurate, it's recommended to use select count(data) from (select unique(col) as data from table) in this case.

Return value type: Integer

Applicable data types: Numeric

Applicable table types: standard tables and supertables

HISTOGRAM

HISTOGRAM(expr, bin_type, bin_description, normalized)

Description: Returns count of data points in user-specified ranges.

Return value type If normalized is set to 1, a DOUBLE is returned; otherwise a BIGINT is returned

Applicable data types: Numeric

Applicable table types: table, STable

Explanations:

• bin_type: parameter to indicate the bucket type, valid inputs are: "user_input", "linear_bin", "log_bin".
• bin_description: parameter to describe how to generate buckets can be in the following JSON formats for each bin_type respectively:

  • "user_input": "[1, 3, 5, 7]": User specified bin values.

  • "linear_bin": "{"start": 0.0, "width": 5.0, "count": 5, "infinity": true}" "start" - bin starting point. "width" - bin offset. "count" - number of bins generated. "infinity" - whether to add (-inf, inf) as start/end point in generated set of bins. The above "linear_bin" descriptor generates a set of bins: [-inf, 0.0, 5.0, 10.0, 15.0, 20.0, +inf].

  • "log_bin": "{"start":1.0, "factor": 2.0, "count": 5, "infinity": true}" "start" - bin starting point. "factor" - exponential factor of bin offset. "count" - number of bins generated. "infinity" - whether to add (-inf, inf) as start/end point in generated range of bins. The above "linear_bin" descriptor generates a set of bins: [-inf, 1.0, 2.0, 4.0, 8.0, 16.0, +inf].

• normalized: setting to 1/0 to turn on/off result normalization. Valid values are 0 or 1.

PERCENTILE

PERCENTILE(expr, p [, p1] ...)

Description: The value whose rank in a specific column matches the specified percentage. If such a value matching the specified percentage doesn't exist in the column, an interpolation value will be returned.

Return value type: This function takes 2 minimum and 11 maximum parameters, and it can simultaneously return 10 percentiles at most. If 2 parameters are given, a single percentile is returned and the value type is DOUBLE. If more than 2 parameters are given, the return value type is a VARCHAR string, the format of which is a JSON ARRAY containing all return values.

Applicable column types: Numeric

Applicable table types: table only

More explanations:

• p is in range [0,100], when p is 0, the result is same as using function MIN; when p is 100, the result is same as function MAX.
• When calculating multiple percentiles of a specific column, a single PERCENTILE function with multiple parameters is advised, as this can largely reduce the query response time. For example, using SELECT percentile(col, 90, 95, 99) FROM table will perform better than SELECT percentile(col, 90), percentile(col, 95), percentile(col, 99) from table.

Selection Functions

Selection functions return one or more results depending. You can specify the timestamp column, tbname pseudocolumn, or tag columns to show which rows contain the selected value.

BOTTOM

BOTTOM(expr, k)

Description: The least k values of a specific column in a table or STable. If a value has multiple occurrences in the column but counting all of them in will exceed the upper limit k, then a part of them will be returned randomly.

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• k must be in range [1,100]
• The timestamp associated with the selected values are returned too
• Can't be used with FILL

FIRST

FIRST(expr)

Description: The first non-null value of a specific column in a table or STable

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• FIRST(*) can be used to get the first non-null value of all columns
• NULL will be returned if all the values of the specified column are all NULL
• A result will NOT be returned if all the columns in the result set are all NULL

INTERP

INTERP(expr [, ignore_null_values])

ignore_null_values: {
    0
  | 1
}

Description: The value that matches the specified timestamp range is returned, if existing; or an interpolation value is returned. The value of ignore_null_values can be 0 or 1, 1 means null values are ignored. The default value of this parameter is 0.

Return value type: Same as the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanations

• INTERP is used to get the value that matches the specified time slice from a column. If no such value exists an interpolation value will be returned based on FILL parameter.
• The input data of INTERP is the value of the specified column and a where clause can be used to filter the original data. If no where condition is specified then all original data is the input.
• INTERP must be used along with RANGE, EVERY, FILL keywords.
• The output time range of INTERP is specified by RANGE(timestamp1,timestamp2) parameter, with timestamp1 <= timestamp2. timestamp1 is the starting point of the output time range. timestamp2 is the ending point of the output time range.
• The number of rows in the result set of INTERP is determined by the parameter EVERY(time_unit). Starting from timestamp1, one interpolation is performed for every time interval specified time_unit parameter. The parameter time_unit must be an integer, with no quotes, with a time unit of: a(millisecond)), s(second), m(minute), h(hour), d(day), or w(week). For example, EVERY(500a) will interpolate every 500 milliseconds.
• Interpolation is performed based on FILL parameter. For more information about FILL clause, see FILL Clause.
• When only one timestamp value is specified in RANGE clause, INTERP is used to generate interpolation at this point in time. In this case, EVERY clause can be omitted. For example, SELECT INTERP(col) FROM tb RANGE('2023-01-01 00:00:00') FILL(linear).
• INTERP can be applied to supertable by interpolating primary key sorted data of all its childtables. It can also be used with partition by tbname when applied to supertable to generate interpolation on each single timeline.
• Pseudocolumn _irowts can be used along with INTERP to return the timestamps associated with interpolation points(support after version 3.0.2.0).
• Pseudocolumn _isfilled can be used along with INTERP to indicate whether the results are original records or data points generated by interpolation algorithm(support after version 3.0.3.0).

Example

• We use the smart meters example used in this documentation to illustrate how to use the INTERP function.
• We want to downsample every 1 hour and use a linear fill for missing values. Note the order in which the "partition by" clause and the "range", "every" and "fill" parameters are used.

SELECT _irowts,INTERP(current) FROM test.meters PARTITION BY TBNAME RANGE('2017-07-22 00:00:00','2017-07-24 12:25:00') EVERY(1h) FILL(LINEAR)

LAST

LAST(expr)

Description: The last non-NULL value of a specific column in a table or STable

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• LAST(*) can be used to get the last non-NULL value of all columns
• If the values of a column in the result set are all NULL, NULL is returned for that column; if all columns in the result are all NULL, no result will be returned.
• When it's used on a STable, if there are multiple values with the timestamp in the result set, one of them will be returned randomly and it's not guaranteed that the same value is returned if the same query is run multiple times.

LAST_ROW

LAST_ROW(expr)

Description: The last row of a table or STable

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanations:

• When it's used on a STable, if there are multiple values with the timestamp in the result set, one of them will be returned randomly and it's not guaranteed that the same value is returned if the same query is run multiple times.
• Can't be used with INTERVAL.

MAX

MAX(expr)

Description: The maximum value of a specific column of a table or STable

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

MIN

MIN(expr)

Description: The minimum value of a specific column in a table or STable

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

MODE

MODE(expr)

Description:The value which has the highest frequency of occurrence. One random value is returned if there are multiple values which have highest frequency of occurrence.

Return value type: Same as the input data

Applicable data types: Numeric

Applicable table types: standard tables and supertables

SAMPLE

SAMPLE(expr, k)

Description: k sampling values of a specific column. The applicable range of k is [1,1000].

Return value type: Same as the column being operated

Applicable data types: Any data type

Applicable nested query: Inner query and Outer query

Applicable table types: standard tables and supertables

TAIL

TAIL(expr, k, offset_val)

Description: The next k rows are returned after skipping the last offset_val rows, NULL values are not ignored. offset_val is optional parameter. When it's not specified, the last k rows are returned. When offset_val is used, the effect is same as order by ts desc LIMIT k OFFSET offset_val.

Parameter value range: k: [1,100] offset_val: [0,100]

Return value type:Same as the data type of the column being operated upon

Applicable data types: Any data type except for timestamp, i.e. the primary key

Applicable table types: standard tables and supertables

TOP

TOP(expr, k)

Description: The greatest k values of a specific column in a table or STable. If a value has multiple occurrences in the column but counting all of them in will exceed the upper limit k, then a part of them will be returned randomly.

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• k must be in range [1,100]
• The timestamp associated with the selected values are returned too
• Can't be used with FILL

UNIQUE

UNIQUE(expr)

Description: The values that occur the first time in the specified column. The effect is similar to distinct keyword.

Return value type:Same as the data type of the column being operated upon

Applicable column types: Any data types

Applicable table types: table, STable

Time-Series Extensions

TDengine includes extensions to standard SQL that are intended specifically for time-series use cases. The functions enabled by these extensions require complex queries to implement in general-purpose databases. By offering them as built-in extensions, TDengine reduces user workload.

CSUM

CSUM(expr)

Description: The cumulative sum of each row for a specific column, NULL value will be discard.

Return value type: Long integer for integers; Double for floating points. uint64_t for unsigned integers

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

More explanations:

• Arithmetic operation can't be performed on the result of csum function
• Can only be used with aggregate functions This function can be used with supertables and standard tables.

DERIVATIVE

DERIVATIVE(expr, time_inerval, ignore_negative)

ignore_negative: {
    0
  | 1
}

Description: The derivative of a specific column. The time rage can be specified by parameter time_interval, the minimum allowed time range is 1 second (1s); the value of ignore_negative can be 0 or 1, 1 means negative values are ignored.

Return value type: DOUBLE

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• It can be used together with a selected column. For example: select _rowts, DERIVATIVE() from.

DIFF

DIFF(expr [, ignore_negative])

ignore_negative: {
    0
  | 1
}

Description: The different of each row with its previous row for a specific column. ignore_negative can be specified as 0 or 1, the default value is 1 if it's not specified. 1 means negative values are ignored.

Return value type:Same as the data type of the column being operated upon

Applicable data types: Numeric

Applicable table types: standard tables and supertables

More explanation:

• The number of result rows is the number of rows subtracted by one, no output for the first row
• It can be used together with a selected column. For example: select _rowts, DIFF() from.

IRATE

IRATE(expr)

Description: instantaneous rate on a specific column. The last two samples in the specified time range are used to calculate instantaneous rate. If the last sample value is smaller, then only the last sample value is used instead of the difference between the last two sample values.

Return value type: DOUBLE

Applicable data types: Numeric

Applicable table types: standard tables and supertables

MAVG

MAVG(expr, k)

Description: The moving average of continuous k values of a specific column. If the number of input rows is less than k, nothing is returned. The applicable range of k is [1,1000].

Return value type: DOUBLE

Applicable data types: Numeric

Nested query: It can be used in both the outer query and inner query in a nested query.

Applicable table types: standard tables and supertables

More explanations:

• Arithmetic operation can't be performed on the result of MAVG.
• Can only be used with data columns, can't be used with tags. - Can't be used with aggregate functions.

STATECOUNT

STATECOUNT(expr, oper, val)

Description: The number of continuous rows satisfying the specified conditions for a specific column. The result is shown as an extra column for each row. If the specified condition is evaluated as true, the number is increased by 1; otherwise the number is reset to -1. If the input value is NULL, then the corresponding row is skipped.

Applicable parameter values:

• oper : Can be one of 'LT' (lower than), 'GT' (greater than), 'LE' (lower than or equal to), 'GE' (greater than or equal to), 'NE' (not equal to), 'EQ' (equal to), the value is case insensitive, the value must be in quotes.
• val: Numeric types

Return value type: Integer

Applicable data types: Numeric

Applicable nested query: Outer query only

Applicable table types: standard tables and supertables

More explanations:

• Can't be used with window operation, like interval/state_window/session_window

STATEDURATION

STATEDURATION(expr, oper, val, unit)

Description: The length of time range in which all rows satisfy the specified condition for a specific column. The result is shown as an extra column for each row. The length for the first row that satisfies the condition is 0. Next, if the condition is evaluated as true for a row, the time interval between current row and its previous row is added up to the time range; otherwise the time range length is reset to -1. If the value of the column is NULL, the corresponding row is skipped.

Applicable parameter values:

• oper : Can be one of 'LT' (lower than), 'GT' (greater than), 'LE' (lower than or equal to), 'GE' (greater than or equal to), 'NE' (not equal to), 'EQ' (equal to), the value is case insensitive, the value must be in quotes.
• val: Numeric types
• unit: The unit of time interval. Enter one of the following options: 1b (nanoseconds), 1u (microseconds), 1a (milliseconds), 1s (seconds), 1m (minutes), 1h (hours), 1d (days), or 1w (weeks) If you do not enter a unit of time, the precision of the current database is used by default.

Return value type: Integer

Applicable data types: Numeric

Applicable nested query: Outer query only

Applicable table types: standard tables and supertables

More explanations:

• Can't be used with window operation, like interval/state_window/session_window

TWA

TWA(expr)

Description: Time weighted average on a specific column within a time range

Return value type: DOUBLE

Applicable data types: Numeric

Applicable table types: standard tables and supertables

System Information Functions

DATABASE

SELECT DATABASE();

Description: The current database. If no database is specified upon logging in and no database is specified with USE after login, NULL will be returned by select database().

CLIENT_VERSION

SELECT CLIENT_VERSION();

Description: The client version.

SERVER_VERSION

SELECT SERVER_VERSION();

Description: The server version.

SERVER_STATUS

SELECT SERVER_STATUS();

Description: The server status.

CURRENT_USER

SELECT CURRENT_USER();

Description: get current user.

Geometry Functions

Geometry Input Functions

Geometry input functions create geometry data from WTK.

ST_GeomFromText

ST_GeomFromText(VARCHAR WKT expr)

Description: Return a specified GEOMETRY value from Well-Known Text representation (WKT).

Return value type: GEOMETRY

Applicable data types: VARCHAR

Applicable table types: standard tables and supertables

Explanations：

• The input can be one of WTK string, like POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION.
• The output is a GEOMETRY data type, internal defined as binary string.

Geometry Output Functions

Geometry output functions convert geometry data into WTK.

ST_AsText

ST_AsText(GEOMETRY geom)

Description: Return a specified Well-Known Text representation (WKT) value from GEOMETRY data.

Return value type: VARCHAR

Applicable data types: GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• The output can be one of WTK string, like POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, GEOMETRYCOLLECTION.

Geometry Relationships Functions

Geometry relationships functions determine spatial relationships between geometries.

ST_Intersects

ST_Intersects(GEOMETRY geomA, GEOMETRY geomB)

Description: Compares two geometries and returns true if they intersect.

Return value type: BOOL

Applicable data types: GEOMETRY, GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• Geometries intersect if they have any point in common.

ST_Equals

ST_Equals(GEOMETRY geomA, GEOMETRY geomB)

Description: Returns TRUE if the given geometries are "spatially equal".

Return value type: BOOL

Applicable data types: GEOMETRY, GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• 'Spatially equal' means ST_Contains(A,B) = true and ST_Contains(B,A) = true, and the ordering of points can be different but represent the same geometry structure.

ST_Touches

ST_Touches(GEOMETRY geomA, GEOMETRY geomB)

Description: Returns TRUE if A and B intersect, but their interiors do not intersect.

Return value type: BOOL

Applicable data types: GEOMETRY, GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• A and B have at least one point in common, and the common points lie in at least one boundary.
• For Point/Point inputs the relationship is always FALSE, since points do not have a boundary.

ST_Covers

ST_Covers(GEOMETRY geomA, GEOMETRY geomB)

Description: Returns TRUE if every point in Geometry B lies inside (intersects the interior or boundary of) Geometry A.

Return value type: BOOL

Applicable data types: GEOMETRY, GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• A covers B means no point of B lies outside (in the exterior of) A.

ST_Contains

ST_Contains(GEOMETRY geomA, GEOMETRY geomB)

Description: Returns TRUE if geometry A contains geometry B.

Return value type: BOOL

Applicable data types: GEOMETRY, GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• A contains B if and only if all points of B lie inside (i.e. in the interior or boundary of) A (or equivalently, no points of B lie in the exterior of A), and the interiors of A and B have at least one point in common.

ST_ContainsProperly

ST_ContainsProperly(GEOMETRY geomA, GEOMETRY geomB)

Description: Returns TRUE if every point of B lies inside A.

Return value type: BOOL

Applicable data types: GEOMETRY, GEOMETRY

Applicable table types: standard tables and supertables

Explanations：

• There is no point of B that lies on the boundary of A or in the exterior of A.