Functions

Aggregate Functions

Aggregate queries are supported in TDengine by the following aggregate functions and selection functions.

COUNT

SELECT COUNT([*|field_name]) FROM tb_name [WHERE clause];

Description: Get the number of rows or the number of non-null values in a table or a super table.

Return value type: Long integer INT64

Applicable column types: All

Applicable table types: table, super table, sub table

More explanation:

• Wildcard (*) is used to represent all columns. The COUNT function is used to get the total number of rows.
• The number of non-NULL values will be returned if this function is used on a specific column.

Examples:

taos> SELECT COUNT(*), COUNT(voltage) FROM meters;
    count(*)        |    count(voltage)     |
================================================
                    9 |                     9 |
Query OK, 1 row(s) in set (0.004475s)

taos> SELECT COUNT(*), COUNT(voltage) FROM d1001;
    count(*)        |    count(voltage)     |
================================================
                    3 |                     3 |
Query OK, 1 row(s) in set (0.001075s)

AVG

SELECT AVG(field_name) FROM tb_name [WHERE clause];

Description: Get the average value of a column in a table or STable

Return value type: Double precision floating number

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

Examples:

taos> SELECT AVG(current), AVG(voltage), AVG(phase) FROM meters;
    avg(current)        |       avg(voltage)        |        avg(phase)         |
====================================================================================
            11.466666751 |             220.444444444 |               0.293333333 |
Query OK, 1 row(s) in set (0.004135s)

taos> SELECT AVG(current), AVG(voltage), AVG(phase) FROM d1001;
    avg(current)        |       avg(voltage)        |        avg(phase)         |
====================================================================================
            11.733333588 |             219.333333333 |               0.316666673 |
Query OK, 1 row(s) in set (0.000943s)

TWA

SELECT TWA(field_name) FROM tb_name WHERE clause;

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

Return value type: Double precision floating number

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

More explanations:

• Since version 2.1.3.0, function TWA can be used on stable with GROUP BY, i.e. timelines generated by GROUP BY tbname on a STable.

IRATE

SELECT IRATE(field_name) FROM tb_name WHERE clause;

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 precision floating number

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

More explanations:

• Since version 2.1.3.0, function IRATE can be used on stble with GROUP BY, i.e. timelines generated by GROUP BY tbname on a STable.

SUM

SELECT SUM(field_name) FROM tb_name [WHERE clause];

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

Return value type: Double precision floating number or long integer

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

Examples:

taos> SELECT SUM(current), SUM(voltage), SUM(phase) FROM meters;
    sum(current)        |     sum(voltage)      |        sum(phase)         |
================================================================================
            103.200000763 |                  1984 |               2.640000001 |
Query OK, 1 row(s) in set (0.001702s)

taos> SELECT SUM(current), SUM(voltage), SUM(phase) FROM d1001;
    sum(current)        |     sum(voltage)      |        sum(phase)         |
================================================================================
            35.200000763 |                   658 |               0.950000018 |
Query OK, 1 row(s) in set (0.000980s)

STDDEV

SELECT STDDEV(field_name) FROM tb_name [WHERE clause];

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

Return value type: Double precision floating number

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable (since version 2.0.15.1)

Examples:

taos> SELECT STDDEV(current) FROM d1001;
    stddev(current)      |
============================
            1.020892909 |
Query OK, 1 row(s) in set (0.000915s)

LEASTSQUARES

SELECT LEASTSQUARES(field_name, start_val, step_val) FROM tb_name [WHERE clause];

Description: The linear regression function of the specified column and the timestamp column (primary key), 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 column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table only

Examples:

taos> SELECT LEASTSQUARES(current, 1, 1) FROM d1001;
            leastsquares(current, 1, 1)             |
=====================================================
{slop:1.000000, intercept:9.733334}                 |
Query OK, 1 row(s) in set (0.000921s)

Selection Functions

When any select function is used, timestamp column or tag columns including tbname can be specified to show that the selected value are from which rows.

MIN

SELECT MIN(field_name) FROM {tb_name | stb_name} [WHERE clause];

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 column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

Examples:

taos> SELECT MIN(current), MIN(voltage) FROM meters;
    min(current)     | min(voltage) |
======================================
            10.20000 |          218 |
Query OK, 1 row(s) in set (0.001765s)

taos> SELECT MIN(current), MIN(voltage) FROM d1001;
    min(current)     | min(voltage) |
======================================
            10.30000 |          218 |
Query OK, 1 row(s) in set (0.000950s)

MAX

SELECT MAX(field_name) FROM { tb_name | stb_name } [WHERE clause];

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 column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

Examples:

taos> SELECT MAX(current), MAX(voltage) FROM meters;
    max(current)     | max(voltage) |
======================================
            13.40000 |          223 |
Query OK, 1 row(s) in set (0.001123s)

taos> SELECT MAX(current), MAX(voltage) FROM d1001;
    max(current)     | max(voltage) |
======================================
            12.60000 |          221 |
Query OK, 1 row(s) in set (0.000987s)

FIRST

SELECT FIRST(field_name) FROM { tb_name | stb_name } [WHERE clause];

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

Return value type: Same as the column being operated upon

Applicable column types: Any data type

Applicable table types: table, STable

More explanations:

• 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

Examples:

taos> SELECT FIRST(*) FROM meters;
        first(ts)        |    first(current)    | first(voltage) |     first(phase)     |
=========================================================================================
2018-10-03 14:38:04.000 |             10.20000 |            220 |              0.23000 |
Query OK, 1 row(s) in set (0.004767s)

taos> SELECT FIRST(current) FROM d1002;
    first(current)    |
=======================
            10.20000 |
Query OK, 1 row(s) in set (0.001023s)

LAST

SELECT LAST(field_name) FROM { tb_name | stb_name } [WHERE clause];

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

Return value type: Same as the column being operated upon

Applicable column types: Any data type

Applicable table types: table, STable

More explanations:

• 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.

Examples:

taos> SELECT LAST(*) FROM meters;
        last(ts)         |    last(current)     | last(voltage) |     last(phase)      |
========================================================================================
2018-10-03 14:38:16.800 |             12.30000 |           221 |              0.31000 |
Query OK, 1 row(s) in set (0.001452s)

taos> SELECT LAST(current) FROM d1002;
    last(current)     |
=======================
            10.30000 |
Query OK, 1 row(s) in set (0.000843s)

TOP

SELECT TOP(field_name, K) FROM { tb_name | stb_name } [WHERE clause];

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 column being operated upon

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

More explanations:

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

Examples:

taos> SELECT TOP(current, 3) FROM meters;
        ts            |   top(current, 3)    |
=================================================
2018-10-03 14:38:15.000 |             12.60000 |
2018-10-03 14:38:16.600 |             13.40000 |
2018-10-03 14:38:16.800 |             12.30000 |
Query OK, 3 row(s) in set (0.001548s)

taos> SELECT TOP(current, 2) FROM d1001;
        ts            |   top(current, 2)    |
=================================================
2018-10-03 14:38:15.000 |             12.60000 |
2018-10-03 14:38:16.800 |             12.30000 |
Query OK, 2 row(s) in set (0.000810s)

BOTTOM

SELECT BOTTOM(field_name, K) FROM { tb_name | stb_name } [WHERE clause];

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 column being operated upon

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

More explanations:

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

Examples:

taos> SELECT BOTTOM(voltage, 2) FROM meters;
        ts            | bottom(voltage, 2) |
===============================================
2018-10-03 14:38:15.000 |                218 |
2018-10-03 14:38:16.650 |                218 |
Query OK, 2 row(s) in set (0.001332s)

taos> SELECT BOTTOM(current, 2) FROM d1001;
        ts            |  bottom(current, 2)  |
=================================================
2018-10-03 14:38:05.000 |             10.30000 |
2018-10-03 14:38:16.800 |             12.30000 |
Query OK, 2 row(s) in set (0.000793s)

PERCENTILE

SELECT PERCENTILE(field_name, P) FROM { tb_name } [WHERE clause];

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: Double precision floating point

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table

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.

Examples:

taos> SELECT PERCENTILE(current, 20) FROM d1001;
percentile(current, 20)  |
============================
            11.100000191 |
Query OK, 1 row(s) in set (0.000787s)

APERCENTILE

SELECT APERCENTILE(field_name, P[, algo_type])
FROM { tb_name | stb_name } [WHERE clause]

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

Return value type: Double precision floating point

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

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.
• algo_type can only be input as default or t-digest, if it's not specified default will be used, i.e. apercentile(column_name, 50) is same as apercentile(column_name, 50, "default").
• When t-digest is used, t-digest sampling is used to calculate. It can be used from version 2.2.0.0.

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

taos> SELECT APERCENTILE(current, 20) FROM d1001;
apercentile(current, 20)  |
============================
            10.300000191 |
Query OK, 1 row(s) in set (0.000645s)

taos> select apercentile (count, 80, 'default') from stb1;
 apercentile (c0, 80, 'default') |
==================================
             601920857.210056424 |
Query OK, 1 row(s) in set (0.012363s)

taos> select apercentile (count, 80, 't-digest') from stb1;
 apercentile (c0, 80, 't-digest') |
===================================
              605869120.966666579 |
Query OK, 1 row(s) in set (0.011639s)

LAST_ROW

SELECT LAST_ROW(field_name) FROM { tb_name | stb_name };

Description: The last row of a table or STable

Return value type: Same as the column being operated upon

Applicable column types: Any data type

Applicable table types: table, STable

More explanations:

• When it's used against a STable, multiple rows with the same and largest timestamp may exist, in this case one of them is returned randomly and it's not guaranteed that the result is same if the query is run multiple times.
• Can't be used with INTERVAL.

Examples:

 taos> SELECT LAST_ROW(current) FROM meters;
 last_row(current)   |
 =======================
             12.30000 |
 Query OK, 1 row(s) in set (0.001238s)

 taos> SELECT LAST_ROW(current) FROM d1002;
 last_row(current)   |
 =======================
             10.30000 |
 Query OK, 1 row(s) in set (0.001042s)

INTERP [Since version 2.3.1]

SELECT INTERP(field_name) FROM { tb_name | stb_name } [WHERE where_condition] [ RANGE(timestamp1,timestamp2) ] [EVERY(interval)] [FILL ({ VALUE | PREV | NULL | LINEAR | NEXT})];

Description: The value that matches the specified timestamp range is returned, if existing; or an interpolation value is returned.

Return value type: Same as the column being operated upon

Applicable column types: Numeric data types

Applicable table types: table, STable, nested query

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.
• 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 and must be specified. timestamp2 is the ending point of the output time range and must be specified. If RANGE is not specified, then the timestamp of the first row that matches the filter condition is treated as timestamp1, the timestamp of the last row that matches the filter condition is treated as timestamp2.
• The number of rows in the result set of INTERP is determined by the parameter EVERY. Starting from timestamp1, one interpolation is performed for every time interval specified EVERY parameter. If EVERY parameter is not used, the time windows will be considered as no ending timestamp, i.e. there is only one time window from timestamp1.
• Interpolation is performed based on FILL parameter. No interpolation is performed if FILL is not used, that means either the original data that matches is returned or nothing is returned.
• INTERP can only be used to interpolate in single timeline. So it must be used with group by tbname when it's used on a STable. It can't be used with GROUP BY when it's used in the inner query of a nested query.
• The result of INTERP is not influenced by ORDER BY TIMESTAMP, which impacts the output order only..

Examples: Based on the meters schema used throughout the documents

• Single point linear interpolation between "2017-07-14 18:40:00" and "2017-07-14 18:40:00:

 taos> SELECT INTERP(current) FROM t1 RANGE('2017-7-14 18:40:00','2017-7-14 18:40:00') FILL(LINEAR);

• Get original data every 5 seconds, no interpolation, between "2017-07-14 18:00:00" and "2017-07-14 19:00:00:

 taos> SELECT INTERP(current) FROM t1 RANGE('2017-7-14 18:00:00','2017-7-14 19:00:00') EVERY(5s);

• Linear interpolation every 5 seconds between "2017-07-14 18:00:00" and "2017-07-14 19:00:00:

  taos> SELECT INTERP(current) FROM t1 RANGE('2017-7-14 18:00:00','2017-7-14 19:00:00') EVERY(5s) FILL(LINEAR);

• Backward interpolation every 5 seconds

  taos> SELECT INTERP(current) FROM t1 EVERY(5s) FILL(NEXT);

• Linear interpolation every 5 seconds between "2017-07-14 17:00:00" and "2017-07-14 20:00:00"

  taos> SELECT INTERP(current) FROM t1 where ts >= '2017-07-14 17:00:00' and ts <= '2017-07-14 20:00:00' RANGE('2017-7-14 18:00:00','2017-7-14 19:00:00') EVERY(5s) FILL(LINEAR);

INTERP [Since version 2.0.15.0]

SELECT INTERP(field_name) FROM { tb_name | stb_name } WHERE ts='timestamp' [FILL ({ VALUE | PREV | NULL | LINEAR | NEXT})];

Description: The value of a specific column that matches the specified time slice

Return value type: Same as the column being operated upon

Applicable column types: Numeric data type

Applicable table types: table, STable

More explanations:

• Time slice must be specified. If there is no data matching the specified time slice, interpolation is performed based on FILL parameter. Conditions such as tags or tbname can be used Where clause can be used to filter data.
• The timestamp specified must be within the time range of the data rows of the table or STable. If it is beyond the valid time range, nothing is returned even with FILL parameter.
• INTERP can be used to query only single time point once. INTERP can be used with EVERY to get the interpolation value every time interval.
• Examples:

 taos> SELECT INTERP(*) FROM meters WHERE ts='2017-7-14 18:40:00.004';
        interp(ts)        |   interp(current)    | interp(voltage) |    interp(phase)     |
 ==========================================================================================
  2017-07-14 18:40:00.004 |              9.84020 |             216 |              0.32222 |
 Query OK, 1 row(s) in set (0.002652s)

If there is no data corresponding to the specified timestamp, an interpolation value is returned if interpolation policy is specified by FILL parameter; or nothing is returned.

 taos> SELECT INTERP(*) FROM meters WHERE tbname IN ('d636') AND ts='2017-7-14 18:40:00.005';
 Query OK, 0 row(s) in set (0.004022s)

 taos> SELECT INTERP(*) FROM meters WHERE tbname IN ('d636') AND ts='2017-7-14 18:40:00.005' FILL(PREV);
        interp(ts)        |   interp(current)    | interp(voltage) |    interp(phase)     |
 ==========================================================================================
  2017-07-14 18:40:00.005 |              9.88150 |             217 |              0.32500 |
 Query OK, 1 row(s) in set (0.003056s)

Interpolation is performed every 5 milliseconds between ['2017-7-14 18:40:00', '2017-7-14 18:40:00.014']

 taos> SELECT INTERP(current) FROM d636 WHERE ts>='2017-7-14 18:40:00' AND ts<='2017-7-14 18:40:00.014' EVERY(5a);
            ts            |   interp(current)    |
 =================================================
  2017-07-14 18:40:00.000 |             10.04179 |
  2017-07-14 18:40:00.010 |             10.16123 |
 Query OK, 2 row(s) in set (0.003487s)

Scalar functions

DIFF

SELECT {DIFF(field_name, ignore_negative) | DIFF(field_name)} FROM tb_name [WHERE clause];

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 column being operated upon

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

More explanations:

• The number of result rows is the number of rows subtracted by one, no output for the first row
• Since version 2.1.30, DIFF can be used on STable with GROUP by tbname

Examples:

taos> SELECT DIFF(current) FROM d1001;
        ts            |    diff(current)     |
=================================================
2018-10-03 14:38:15.000 |              2.30000 |
2018-10-03 14:38:16.800 |             -0.30000 |
Query OK, 2 row(s) in set (0.001162s)

DERIVATIVE

SELECT DERIVATIVE(field_name, time_interval, ignore_negative) FROM tb_name [WHERE clause];

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 precision floating point

Applicable column types: Data types except for timestamp, binary, nchar and bool

Applicable table types: table, STable

More explanations:

• It is available since version 2.1.3.0, the number of result rows is the number of total rows in the time range subtracted by one, no output for the first row.
• It can be used together with GROUP BY tbname against a STable.

Examples:

taos> select derivative(current, 10m, 0) from t1;
           ts            | derivative(current, 10m, 0) |
========================================================
 2021-08-20 10:11:22.790 |                 0.500000000 |
 2021-08-20 11:11:22.791 |                 0.166666620 |
 2021-08-20 12:11:22.791 |                 0.000000000 |
 2021-08-20 13:11:22.792 |                 0.166666620 |
 2021-08-20 14:11:22.792 |                -0.666666667 |
Query OK, 5 row(s) in set (0.004883s)

SPREAD

SELECT SPREAD(field_name) FROM { tb_name | stb_name } [WHERE clause];

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

Return value type: Double precision floating point

Applicable column types: Data types except for binary, nchar, and bool

Applicable table types: table, STable

More explanations: Can be used on a column of TIMESTAMP type, the result is the time range size.

Examples:

taos> SELECT SPREAD(voltage) FROM meters;
    spread(voltage)      |
============================
            5.000000000 |
Query OK, 1 row(s) in set (0.001792s)

taos> SELECT SPREAD(voltage) FROM d1001;
    spread(voltage)      |
============================
            3.000000000 |
Query OK, 1 row(s) in set (0.000836s)

CEIL

SELECT CEIL(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The rounded up value of a specific column

Return value type: Same as the column being used

Applicable data types: Data types except for timestamp, binary, nchar, bool

Applicable table types: table, STable

Applicable nested query: Inner query and outer query

More explanations:

• Can't be used on any tags of any type
• Arithmetic operation can be performed on the result of ceil function
• Can't be used with aggregate functions

FLOOR

SELECT FLOOR(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The rounded down value of a specific column

More explanations: The restrictions are same as those of the CEIL function.

ROUND

SELECT ROUND(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The rounded value of a specific column.

More explanations: The restrictions are same as CEIL function.

CSUM

    SELECT CSUM(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The cumulative sum of each row for a specific column. The number of output rows is same as that of the input rows.

Return value type: Long integer for integers; Double for floating points. Timestamp is returned for each row.

Applicable data types: Data types except for timestamp, binary, nchar, and bool

Applicable table types: table, STable

Applicable nested query: Inner query and Outer query

More explanations:

• Can't be used on tags when it's used on STable
• Arithmetic operation can't be performed on the result of csum function
• Can only be used with aggregate functions
• Group by tbname must be used together on a STable to force the result on a single timeline

Applicable versions: Since 2.3.0.x

MAVG

    SELECT MAVG(field_name, K) FROM { tb_name | stb_name } [WHERE clause]

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 is k is [1,1000].

Return value type: Double precision floating point

Applicable data types: Data types except for timestamp, binary, nchar, and bool

Applicable nested query: Inner query and Outer query

Applicable table types: table, STable

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.
• Must be used with GROUP BY tbname when it's used on a STable to force the result on each single timeline.

Applicable versions: Since 2.3.0.x

SAMPLE

    SELECT SAMPLE(field_name, K) FROM { tb_name | stb_name } [WHERE clause]

Description: k sampling values of a specific column. The applicable range of k is [1,10000]

Return value type: Same as the column being operated plus the associated timestamp

Applicable data types: Any data type except for tags of STable

Applicable table types: table, STable

Applicable nested query: Inner query and Outer query

More explanations:

• Arithmetic operation can't be operated on the result of SAMPLE function
• Must be used with Group by tbname when it's used on a STable to force the result on each single timeline

Applicable versions: Since 2.3.0.x

Arithmetic Operations

SELECT field_name [+|-|*|/|%][Value|field_name] FROM { tb_name | stb_name }  [WHERE clause];

Description: The sum, difference, product, quotient, or remainder between one or more columns

Return value type: Double precision floating point

Applicable column types: Data types except for timestamp, binary, nchar, bool

Applicable table types: table, STable

More explanations:

• Arithmetic operations can be performed on two or more columns. Parentheses () can be used to control the order of precedence.
• NULL doesn't participate in the operation i.e. if one of the operands is NULL then result is NULL

Examples:

taos> SELECT current + voltage * phase FROM d1001;
(current+(voltage*phase)) |
============================
            78.190000713 |
            84.540003240 |
            80.810000718 |
Query OK, 3 row(s) in set (0.001046s)