两类存储过程：函数和过程的区别

Calling	Only with CALL	Possible in all SQL commands, e.g., in SELECT and UPDATE commands.
Return	Can return one or more SELECT results	Returns a single value (command RETURN); the data type of the return value must be specified in the declaration with RETURNS.
Parameters	Value and reference parameters possible (IN, OUT, INOUT)	Only value parameters allowed, thus no identification with IN, etc.
Commands allowed in the code	All SQL commands, including SELECT, INSERT, UPDATE, DELETE, CREATE TABLE	No commands that access tables.
Calling other functions and procedures	May call other procedures and functions	May call only functions, not procedures.

 

It is permitted to have a function and a procedure with the same name, since when
it is called, MySQL can tell whether a function or a procedure is being invoked.