statement-label
If the ending statement-label is specified, it must match the beginning statement-label. The LEAVE statement can be used to resume execution at the first statement after the compound statement. The compound statement
that is the body of a procedure or trigger has an implicit label that is the same as the name of the procedure or trigger.
ATOMIC clause
An atomic statement is a statement that is executed completely or not at all. For example, an UPDATE statement that updates
thousands of rows might encounter an error after updating many rows. If the statement does not complete, all changes revert
back to their original state. Similarly, if you specify that the BEGIN statement is atomic, the statement is executed either
in its entirety or not at all.
local-declaration
Immediately following the BEGIN, a compound statement can have local declarations for objects that only exist within
the compound statement. A compound statement can have a local declaration for a variable, a cursor, a temporary table, or
an exception. Local declarations can be referenced by any statement in that compound statement, or in any compound statement
nested within it. Local declarations of the compound statement are visible to the exception handlers for the statement. Local
declarations are not visible to other procedures that are called from within a compound statement.
The body of a procedure or trigger is a compound statement. Compound statements can also be used in control statements within
a procedure or trigger.
A compound statement allows one or more SQL statements to be grouped together and treated as a unit. A compound statement
starts with the keyword BEGIN and ends with the keyword END.
The body of a procedure or trigger is a compound statement.
CREATE PROCEDURE TopCustomer (OUT TopCompany CHAR(35), OUT TopValue INT)
BEGIN
DECLARE err_notfound EXCEPTION FOR
SQLSTATE '02000';
DECLARE curThisCust CURSOR FOR
SELECT CompanyName, CAST(
sum( SalesOrderItems.Quantity *
Products.UnitPrice ) AS INTEGER) VALUE
FROM Customers
LEFT OUTER JOIN SalesOrders
LEFT OUTER JOIN SalesOrderItems
LEFT OUTER JOIN Products
GROUP BY CompanyName;
DECLARE ThisValue INT;
DECLARE ThisCompany CHAR( 35 );
SET TopValue = 0;
OPEN curThisCust;
CustomerLoop:
LOOP
FETCH NEXT curThisCust
INTO ThisCompany, ThisValue;
IF SQLSTATE = err_notfound THEN
LEAVE CustomerLoop;
END IF;
IF ThisValue > TopValue THEN
SET TopValue = ThisValue;
SET TopCompany = ThisCompany;
END IF;
END LOOP CustomerLoop;
CLOSE curThisCust;
END;
The example below declares the following variables:
v1 as an INT with the initial setting of 5.
v2 and v3 as CHAR(10), both with an initial value of abc.
BEGIN
DECLARE v1 INT = 5
DECLARE v2, v3 CHAR(10) = 'abc'
// ...
END