根据case when子句的条件执行不同的准备语句

Question

我是MySQL的初学者，我正试图根据case-when子句中的条件执行不同的准备语句。问题是要找到STATION表的LAT_N列的中值，对于偶数和奇数条LAT_N记录，我想使用Case。

这是我为特殊情况准备的声明：

SET @foo = (SELECT ROUND((COUNT(*)-1)/2) FROM STATION);
PREPARE STMT1 FROM 'SELECT ROUND(LAT_N,4) FROM STATION ORDER BY LAT_N LIMIT ?,1';
EXECUTE STMT1 USING @foo;

这是为偶数：

SET @foo1 = (SELECT ROUND(COUNT(*)/2) FROM STATION);
SET @foo2 = (SELECT ROUND((COUNT(*)+2)/2) FROM STATION);
PREPARE STMT2 FROM 'SELECT ROUND((((SELECT ROUND(LAT_N,4) FROM STATION ORDER BY LAT_N LIMIT ?,1) + (SELECT ROUND(LAT_N,4) FROM STATION ORDER BY LAT_N LIMIT ?,1))/2),4)';
EXECUTE STMT2 USING @foo1, @foo2;

我的想法与这个代码有点相似：

SELECT CASE WHEN COUNT(*)%2=0 THEN EXECUTE STMT2 USING @foo1, @foo2
ELSE EXECUTE STMT1 USING @foo
FROM STATION
END;

但该代码返回错误1064(42000(，所以我想知道是否有其他选择。非常感谢

Answer 1

我已经找到了答案，其中包括使用过程

DELIMITER $$
CREATE PROCEDURE latmed()
BEGIN 
IF (SELECT COUNT(*) FROM STATION)%2=0 THEN
SET @foo1 = (SELECT ROUND(COUNT(*)/2) FROM STATION);
SET @foo2 = (SELECT ROUND((COUNT(*)+2)/2) FROM STATION);
PREPARE STMT2 FROM 'SELECT ROUND((((SELECT ROUND(LAT_N,4) FROM STATION ORDER BY LAT_N LIMIT ?,1) + (SELECT ROUND(LAT_N,4) FROM STATION ORDER BY LAT_N LIMIT ?,1))/2),4)';
EXECUTE STMT2 USING @foo1, @foo2;
ELSE
SET @foo = (SELECT ROUND((COUNT(*)-1)/2) FROM STATION);
PREPARE STMT1 FROM 'SELECT ROUND(LAT_N,4) FROM STATION ORDER BY LAT_N LIMIT ?,1';
EXECUTE STMT1 USING @foo;
END IF;
END$$
DELIMITER ;
CALL latmed()

我认为它有点长，所以如果有人有一个较短的代码可以回答我的问题。感谢