DELETE

Function

Delete data from an HStore table.

• To use hybrid data warehouse capabilities, choose the storage-compute coupled architecture when you create a GaussDB(DWS) cluster on the console and ensure the vCPU to memory ratio is 1:4 when setting up cloud disk flavors. For more information, see Data Warehouse Flavors.
• When setting up a GaussDB(DWS) cluster, make sure to have a vCPU to memory ratio of 1:8 for standard data warehouses and a ratio of 1:4 for hybrid data warehouses. You can distinguish a standard data warehouse from a real-time data warehouse by comparing their vCPU to memory ratios.

Precautions

• To efficiently remove all data from a table and prevent it from becoming bloated, use the TRUNCATE syntax.
• If a single record is deleted from an HStore table, a record of the type D will be inserted into the delta table. The memory update chain will also be updated to manage concurrency.
• If multiple records are deleted from an HStore table at a time, a record of the type D will be inserted for the consecutive deleted records in each CU.
• In concurrent deletion scenarios, operations on the same CU will get queued in traditional column-store tables and result in low performance. For HStore tables, the operations can be concurrently performed, and the deletion performance can be more than 100 times that of column-store tables.
• The syntax is fully compatible with column storage. For more information, see the UPDATE syntax.

Syntax

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DELETE FROM [ ONLY ] table_name [ * ] [ [ AS ] alias ]
    [ USING using_list ]
    [ WHERE condition ]

Parameters

• ONLY

  If ONLY is specified, only that table is deleted. If ONLY is not specified, this table and all its sub-tables are deleted.

• table_name

  Specifies the name (optionally schema-qualified) of a target table.

  Value range: an existing table name

• alias

  Specifies the alias for the target table.

  Value range: a string. It must comply with the naming convention.

• using_list

  Specifies the USING clause.

• condition

  Specifies an expression that returns a value of type boolean. Only rows for which this expression returns true will be deleted.

Example

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CREATE TABLE reason_t2
(
    TABLE_SK          INTEGER               ,
    TABLE_ID          VARCHAR(20)           ,
    TABLE_NA          VARCHAR(20)
)WITH(ORIENTATION=COLUMN, ENABLE_HSTORE=ON);
INSERT INTO reason_t2 VALUES (1, 'S01', 'StudentA'),(2, 'T01', 'TeacherA'),(3, 'T02', 'TeacherB');

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DELETE FROM reason_t2 WHERE TABLE_SK = 2;
DELETE FROM reason_t2 AS rt2 WHERE rt2.TABLE_SK = 2;

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DELETE FROM reason_t2 WHERE TABLE_SK in (1,3);