如何设置一个变量来存储 select 语句返回的值并在存储过程 MySQL 中执行操作？

Question

1. Operation should perform according to value passed through parameter
2. A value should be returned using SELECT statement to a variable
3. Perform any operation and assign it to another variable.
4. UPDATE table using new value

Answer 1

CREATE PROCEDURE `DepositToAcct`(ACC_NUM BIGINT,DEP_AMNT DOUBLE)
BEGIN
    DECLARE OLD_BAL DOUBLE;
    DECLARE NEW_BAL DOUBLE DEFAULT 0;

    SELECT BALANCE  INTO OLD_BAL 
    FROM account_details WHERE ACCOUNT_NUMBER= ACC_NUM;

    SET NEW_BAL = OLD_BAL+DEP_AMNT;

    UPDATE account_details 
    SET BALANCE=NEW_BAL 
    WHERE ACCOUNT_NUMBER= ACC_NUM;
END