BEGIN

Description

Starts a transaction using BEGIN. If an isolation level and a read/write mode are specified, a new transaction will have those characteristics. You can also specify them using SET TRANSACTION.

Precautions

None

Syntax

Start a transaction.

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 a transaction isolation level, which determines what data is visible to a transaction if there are other concurrent transactions.

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, this isolation level is not supported in an M-compatible database. It 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;