Updated on 2025-05-29 GMT+08:00

START TRANSACTION

Description

Starts a transaction. If the isolation level or read/write mode is specified, a new transaction will have those characteristics. You can also specify them using SET TRANSACTION.

Precautions

When START TRANSACTION is used, autocommit remains disabled and is not restored to the initial state until you run COMMIT or ROLLBACK to end a transaction.

Syntax

Format 1: START TRANSACTION

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START TRANSACTION
  [ 
    { 
       ISOLATION LEVEL { READ COMMITTED | READ UNCOMMITTED | SERIALIZABLE | REPEATABLE READ }
       | { READ WRITE | READ ONLY }
     } [, ...] 
  ];

Format 2: BEGIN

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BEGIN [ WORK | TRANSACTION ]
  [ 
    { 
       ISOLATION LEVEL { READ COMMITTED | READ UNCOMMITTED | SERIALIZABLE | REPEATABLE READ }
       | { READ WRITE | READ ONLY }
      } [, ...] 
  ];

Parameters

  • WORK | TRANSACTION

    Specifies the optional keyword in BEGIN format without functions.

  • ISOLATION LEVEL

    Specifies the transaction isolation level that determines the data that a transaction can view if other concurrent transactions exist.

    The isolation level of a transaction cannot be reset after the first clause (INSERT, DELETE, UPDATE, FETCH, COPY) for modifying data is executed in the transaction.

    Value range:

    • READ COMMITTED: Only committed data is read. This is the default value.
    • READ UNCOMMITTED: After this isolation level is set, its behavior is the same as that of READ COMMITTED.
    • REPEATABLE READ: Only the data committed before transaction start is read. Uncommitted data or data committed in other concurrent transactions cannot be read.
    • SERIALIZABLE: Currently, GaussDB does not support this isolation level. Setting this isolation level is equivalent to REPEATABLE READ.
  • READ WRITE | READ ONLY

    Specifies the transaction access mode (read/write or read only).

Examples

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-- Create a schema.
gaussdb=# CREATE SCHEMA tpcds;

-- Create the tpcds.reason table.
gaussdb=# CREATE TABLE tpcds.reason (c1 int, c2 int);

-- Start a transaction in default mode.
gaussdb=# START TRANSACTION;
gaussdb=# SELECT * FROM tpcds.reason;
gaussdb=# END;

-- Start a transaction in default mode.
gaussdb=# BEGIN;
gaussdb=# SELECT * FROM tpcds.reason;
gaussdb=# END;

-- Start a transaction with the isolation level being READ COMMITTED and the access mode being READ WRITE:
gaussdb=# START TRANSACTION ISOLATION LEVEL READ COMMITTED READ WRITE;
gaussdb=# SELECT * FROM tpcds.reason;
gaussdb=# COMMIT;

-- Delete the table.
gaussdb=# DROP TABLE tpcds.reason;

-- Delete the schema.
gaussdb=# DROP SCHEMA tpcds CASCADE;

Helpful Links

COMMIT | END, ROLLBACK, and SET TRANSACTION