In / out / inout details of MySQL stored procedures

IN

No matter how the parameters in the stored procedure are changed , Will not affect external variables .

OUT

No matter what is defined before the parameter is passed in , In the stored procedure, it is NULL.

Parameter changes in stored procedures , Will affect external variables .

INOUT

Parameters are defined externally , The defined variables will be passed into （ Feel similar Java Object address value ）.

Parameter changes in stored procedures , Will affect external variables .

The following is the actual application

#  If it already exists, delete 
DROP PROCEDURE IF EXISTS getAreaCode;

#  Create stored procedure pairs areaCode To deal with 
DELIMITER $$
CREATE PROCEDURE getAreaCode(INOUT areaCode VARCHAR(12))
BEGIN	
	CASE 
		WHEN SUBSTR(areaCode, 3, 2) = '00' THEN SET areaCode = SUBSTR(areaCode, 1, 2);
		WHEN SUBSTR(areaCode, 5, 2) = '00' THEN SET areaCode = SUBSTR(areaCode, 1, 4);
		WHEN SUBSTR(areaCode, 7, 3) = '000' THEN SET areaCode = SUBSTR(areaCode, 1, 6);
		WHEN SUBSTR(areaCode, 10, 3) = '000' THEN SET areaCode = SUBSTR(areaCode, 1, 9);
	END CASE;
END $$

#  Inner Mongolia , Hohhot, , New town 
SET @areaCode = '150102000000';

CALL getAreaCode(@areaCode);

#  Query the data under the new urban area  
SELECT * FROM case_report WHERE case_area_code LIKE CONCAT(@areaCode,'%');