START TRANSACTION

Function

START TRANSACTION 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

None

Syntax

Format 1: START TRANSACTION

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

Format 2: BEGIN

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

Parameter Description

• 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.

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

  Value range:

  • READ COMMITTED: Only submitted data is read. It is the default value.
  • 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, this isolation level is not supported in MogDB. It is equivalent to REPEATABLE READ.

• READ WRITE | READ ONLY

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

Examples

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

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

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