luhuayi 85562e1879 DWS UMN 831.100 version

Reviewed-by: Pruthi, Vineet <vineet.pruthi@t-systems.com>
Co-authored-by: luhuayi <luhuayi@huawei.com>
Co-committed-by: luhuayi <luhuayi@huawei.com>

2024-11-13 08:55:54 +00:00

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How Do I Delete Table Data Efficiently in GaussDB(DWS)?

Yes. TRUNCATE is more efficient than DELETE for deleting massive data.

Function

TRUNCATE quickly removes all rows from a table. It has the same effect as an unqualified DELETE but since it does not actually scan the table it is faster. This is most effective on large tables.

Functions

TRUNCATE TABLE works like a DELETE statement with no WHERE clause, that is, emptying a table.
TRUNCATE TABLE uses less system and transaction log resources.
- DELETE deletes a row each time, and records each deletion in the transaction log.
- TRUNCATE TABLE deletes all rows in a table by releasing the data page, and only records each releasing of the data page in the transaction log.
TRUNCATE, DELETE, and DROP are different in that:
- TRUNCATE TABLE deletes content, releases space, but does not delete definitions.
- DELETE TABLE deletes content, but does not delete definitions or release space.
- DROP TABLE deletes content and definitions, and releases space.

Examples

Create a table.

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CREATE TABLE tpcds.reason_t1 AS TABLE tpcds.reason;

Truncate the table.

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TRUNCATE TABLE tpcds.reason_t1;

Delete the table.

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DROP TABLE tpcds.reason_t1;

Create a partitioned table.

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CREATE TABLE tpcds.reason_p
(
  r_reason_sk integer,
  r_reason_id character(16),
  r_reason_desc character(100)
)PARTITION BY RANGE (r_reason_sk)
(
  partition p_05_before values less than (05),
  partition p_15 values less than (15),
  partition p_25 values less than (25),
  partition p_35 values less than (35),
  partition p_45_after values less than (MAXVALUE)
);

Insert data.

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INSERT INTO tpcds.reason_p SELECT * FROM tpcds.reason;

Truncate the p_05_before partition.

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ALTER TABLE tpcds.reason_p TRUNCATE PARTITION p_05_before;

Truncate the partition p_15 where 13 is located.

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ALTER TABLE tpcds.reason_p TRUNCATE PARTITION for (13);

Truncate the partitioned table.

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TRUNCATE TABLE tpcds.reason_p;