13.6.1 BEGIN ... END Compound-Statement Syntax
BEGIN ... END syntax is used for writing compound statements, which can appear within stored programs(stored procedures and functions, trigger, and events). A compound statement can contain multiple statements, enclosed by the BEGIN and END keywords. statement_list represents a list of one or more statements, each terminated by a semicolon(;) statement delimiter. The statement_list itself is optional, so the empty compound statement(BEGIN END) is legal. BEGIN ... END blocks can be nested.
Use of multiple statements requires that a client is able to send statement strings contains the ; statement delimiter. In the mysql command-line client, this is handled with the delimiter command. Changing the ; end-of-statement delimiter(for example, to //) permit ; to be used in a program body. For an example, see Section 23.1, "Defining Stored Programs".
A BEGIN ... END block can be labeled. See Section 13.6.2, "Statement Label Syntax".
The optional [NOT] ATOMIC clause is not supported. This means that no transactional savepoint is set at the start of the instruction block and the BEGIN clause used in this context has no effect on the current transaction.
NOTE
Within all stored programs, the parser treats BEGIN [WORK] as the beginning of a BEGIN ... END block. To begin a transaction in this context, use START TRANSACTION instead.