38.4. User-Defined Procedures

38.4. User-Defined Procedures
Prev	Up	Chapter 38. Extending SQL	Home	Next

+ 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 + PROCEDURE lacks a RETURNS clause. + 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 CALL command 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. +

Prev	Up	Next
38.3. User-Defined Functions	Home	38.5. Query Language (SQL) Functions