Delete Data

TDengine provides the functionality of deleting data from a table or STable according to specified time range, it can be used to cleanup abnormal data generated due to device failure.

Note：Deletting some data doesn't release the disk space occupied by the table, instead all the rows in the table are marked as deleted, so these data will not occur when querying. The disk space will be released when the system automatically performs compact operation or the user performs compact manually.

Syntax:

DELETE FROM [ db_name. ] tb_name [WHERE condition];

Description: Delete data from a table or STable

Parameters:

• db_name: Optional parameter, specifies the database in which the table exists; if not specified, the current database will be used.
• tb_name: Mandatory parameter, specifies the table name from which data will be deleted, it can be normal table, subtable or STable.
• condition: Optional parameter, specifies the data filter condition. If no condition is specified all data will be deleted, so please be cautions to delete data without any condition. The condition used here is only applicable to the first column, i.e. the timestamp column.

More Explanations:

The data can't be recovered once deleted, so please be cautious to use the functionality of deleting data. It's better to firstly make sure the data to be deleted using select then execute delete.

Example:

meters is a STable, in which groupid is a tag column of int type. Now we want to delete the data older than 2021-10-01 10:40:00.100. You can perform this action by running the following SQL statement:

delete from meters where ts < '2021-10-01 10:40:00.100' ;

The output is:

Deleted 102000 row(s) from 1020 table(s) (0.421950s)

It means totally 102,000 rows of data have been deleted from 1,020 sub tables.