mysql - 在 MySQL 嵌套 If 中检查 Null

Question

我正在尝试编写一个 MySQL 函数，该函数从格式化为 JSON 字典的文本字段中提取值。但是，由于某种原因，我无法让嵌套的 IF 语句在没有语法错误的情况下工作。

这是函数:

DROP FUNCTION IF EXISTS json_key;
DELIMITER $$

CREATE FUNCTION `json_key`(`col` TEXT, `key` VARCHAR(255)) RETURNS VARCHAR(255)
DETERMINISTIC
BEGIN
    DECLARE ret VARCHAR(255);
    DECLARE pos INT;
    IF (col IS NULL) THEN SET ret = "";
    ELSEIF (col = "") THEN SET ret =  "";
    ELSEIF (LOCATE(key, col) = 0) THEN SET ret =  "";
    ELSE 
        SET pos := LOCATE(key, col);
        SET len := LENGTH(key);
        SET bg  := pos + len;
        SET ret = SUBSTR(col, bg, LOCATE('"', col, bg) - bg));
    END IF;
    RETURN ret;
END $$
DELIMITER ;

这是我收到的错误:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to 
use near 'key, col) = 0) THEN SET ret =  "";

ELSE 
SET pos := LOCATE(key, col);
SET len :=' at line 7

知道我缺少什么吗？

Answer 1

key 是保留字。

使用不同的名称，例如 jKey 或使用反引号 (`) 来接受它

更改这些行:

ELSEIF (LOCATE(key, col) = 0) THEN SET ret =  "";
ELSE 
    SET pos := LOCATE(key, col);
    SET len := LENGTH(key);

致:

ELSEIF (LOCATE(`key`, col) = 0) THEN SET ret =  "";
ELSE 
    SET pos := LOCATE(`key`, col);
    SET len := LENGTH(`key`);

引用:MySQL Reserved Words