BEGIN

Description

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

Precautions

None

Syntax

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

Parameters

• WORK | TRANSACTION

  Specifies an optional keyword in the BEGIN format and does not have any actual effect.

• ISOLATION LEVEL

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

  

  The isolation level cannot be changed after data is modified using SELECT, INSERT, DELETE, UPDATE, or COPY in the transaction.

  Value range:

  • READ COMMITTED: Only committed data can be 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 the transaction starts can be read. Uncommitted data or data committed in other concurrent transactions cannot be read.
  • SERIALIZABLE: Currently, the M-compatible database 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

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

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

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

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

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

-- Drop the tpcds.reason table.
m_db=# DROP TABLE tpcds.reason;

-- Delete a schema.
m_db=# DROP SCHEMA tpcds;

Helpful Links

START TRANSACTION