START TRANSACTION

Function

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

Precautions

None

Syntax

Format 1: START TRANSACTION

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

Format 2: BEGIN

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

Parameter Description

WORK | TRANSACTION
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.

Valid value:
- READ COMMITTED: Only committed data is read. This is the default.
- READ UNCOMMITTED: GaussDB(DWS) does not support READ UNCOMMITTED. If READ UNCOMMITTED is set, READ COMMITTED is executed instead.
- REPEATABLE READ: Only the data committed before transaction start is read. Uncommitted data or data committed in other concurrent transactions cannot be read.
- SERIALIZABLE: GaussDB(DWS) does not support SERIALIZABLE. If SERIALIZABLE is set, REPEATABLE READ is executed instead.
READ WRITE | READ ONLY
Specifies the transaction access mode (read/write or read only).

Examples

Start a transaction in default mode.

      
           START TRANSACTION;
CREATE TABLE IF NOT EXISTS table1 (a int,b int);
SELECT * FROM table1;
END;

Start a transaction with the isolation level being READ COMMITTED and the access mode being READ WRITE:

      
           START TRANSACTION ISOLATION LEVEL READ COMMITTED READ WRITE;
CREATE TABLE IF NOT EXISTS table1 (a int,b int);
SELECT * FROM table1;
COMMIT;