Detailed explanation of the entry-level use of MySql stored procedure parameters

-- Usage of in parameters in stored procedures DELIMITER ;; 
CREATE PROCEDURE 
name_in(IN `time` VARCHAR(50)) 
BEGIN
 
 
SELECT NOW() ,`time`;
 
END ;;
CALL name_in('now time'); -- in is a formal parameter. You can define the data type and give the actual parameter DELIMITER when calling the stored procedure;; 
CREATE PROCEDURE name_in_2(IN `time` VARCHAR(50)) -- Use BEGIN for set assignment
 
 
SELECT NOW() ,`time`;
 
END ;;
SET @wo='now time'; 
CALL name_in_2(@wo);
 
DELIMITER ;; 
CREATE PROCEDURE name_in_4(IN `time` VARCHAR(50)) -- DECLARE creates a variable using BEGIN
DECLARE `time` DEFAULT 'wo'; -- DECLARE creates a variable that is only valid in the begin-end statement block SELECT NOW() ,`time`;-- 
END ;;
-- You can use DECLARE in a stored procedure -- Create (DECLARE) and assign (SET) values ​​set @variable name = value -- In summary, DECLARE is only valid in the begin-end statement block. Adding @ to set means that the session variable is valid for the connected client in the current connection. 

DELIMITER ;; 
CREATE PROCEDURE name_out(IN `one` INT , IN two INT ,OUT shu INT) -- Use of out output parameter BEGIN
 
SET shu=`one`+two; -- directly add two input parameters and assign them to the output parameter set. The variable name means assignment -- set assignment is valid in the current stored procedure. For example, you can use select shu;
 -- set @The value assigned is valid in the currently connected client END ;;
 
 
CALL name_out(3,3,@shuchu);
SELECT @shuchu AS output parameter; -- When calling a stored procedure, you can define an @ parameter to receive the output parameter, that is, the return value.