I am trying to write a MySQL function that pulls a value out of a text field that is formatted as a JSON dict. However, for some reason I can't get the nested IF statement to work without syntax errors.

Here is the function:

```
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 ;

```

Here is the error I am getting:

```
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

```

Any idea on what I'm missing?