如何检查变量是否为NULL，然后使用MySQL存储过程进行设置？

Question

我有一个MySQL存储过程，可以从表中找到最大值。

如果没有值，我想将变量设置为昨天的日期。

DECLARE current_procedure_name CHAR(60) DEFAULT 'accounts_general';
DECLARE last_run_time datetime DEFAULT NULL;
DECLARE current_run_time datetime DEFAULT NOW();

-- Define the last run time
SET last_run_time := (SELECT MAX(runtime) 
FROM dynamo.runtimes WHERE procedure_name = @current_procedure_name);

-- if there is no last run time found then use yesterday as starting point
IF(@last_run_time IS NULL) THEN
    SET last_run_time := DATE_SUB( NOW(), INTERVAL 1 DAY);
END IF;

SELECT @last_run_time;

问题是@last_run_time总是NULL。

由于某些原因，以下代码未执行

IF(last_run_time IS NULL) THEN
    SET last_run_time := DATE_SUB( NOW(), INTERVAL 1 DAY);
END IF;

如何@last_run_time正确设置变量？

Answer 1

@last_run_time是9.4。用户定义的变量和last_run_time datetime一个13.6.4.1。局部变量DECLARE语法是不同的变量。

尝试： SELECT last_run_time;

更新

例：

/* CODE FOR DEMONSTRATION PURPOSES */
DELIMITER $$

CREATE PROCEDURE `sp_test`()
BEGIN
    DECLARE current_procedure_name CHAR(60) DEFAULT 'accounts_general';
    DECLARE last_run_time DATETIME DEFAULT NULL;
    DECLARE current_run_time DATETIME DEFAULT NOW();

    -- Define the last run time
    SET last_run_time := (SELECT MAX(runtime) FROM dynamo.runtimes WHERE procedure_name = current_procedure_name);

    -- if there is no last run time found then use yesterday as starting point
    IF(last_run_time IS NULL) THEN
        SET last_run_time := DATE_SUB(NOW(), INTERVAL 1 DAY);
    END IF;

    SELECT last_run_time;

    -- Insert variables in table2
    INSERT INTO table2 (col0, col1, col2) VALUES (current_procedure_name, last_run_time, current_run_time);
END$$

DELIMITER ;