37.4. User-Defined Procedures
A procedure is a database object similar to a function. The key differences are:
-
Procedures are defined with the CREATE PROCEDURE command, not
CREATE FUNCTION. -
Procedures do not return a function value; hence
CREATE PROCEDURElacks aRETURNSclause. However, procedures can instead return data to their callers via output parameters. -
While a function is called as part of a query or DML command, a procedure is called in isolation using the CALL command.
-
A procedure can commit or roll back transactions during its execution (then automatically beginning a new transaction), so long as the invoking
CALLcommand is not part of an explicit transaction block. A function cannot do that. -
Certain function attributes, such as strictness, don't apply to procedures. Those attributes control how the function is used in a query, which isn't relevant to procedures.
The explanations in the following sections about how to define user-defined functions apply to procedures as well, except for the points made above.
Collectively, functions and procedures are also known
as
routines
.
There are commands such as
ALTER ROUTINE
and
DROP ROUTINE
that can operate on functions and
procedures without having to know which kind it is. Note, however, that
there is no
CREATE ROUTINE
command.