SQL if判断
SELECT Menu_Id, IF EXISTS(SELECT Menu_Id FROM cy_bt_Menu_Unit WHERE (Menu_Id = 'Menu_Id')) '存在' ELSE '不存在' AS d
FROM cy_bt_Menu_Info


判断 复制D
这个语句怎么不对啊！


[最优解释]
SELECT Menu_Id, case when EXISTS(SELECT 1 FROM cy_bt_Menu_Unit WHERE Menu_Id = a.Menu_Id) then '存在' ELSE '不存在' end AS d
FROM cy_bt_Menu_Info as a
[其他解释]
SELECT Menu_Id, CASE (SELECT COUNT(Menu_Id) FROM cy_bt_Menu_Unit WHERE (Menu_Id = 'Menu_Id')) WHEN 0 THEN '存在' ELSE '不存在' END AS d
FROM cy_bt_Menu_Info

[其他解释]
要用case when

SELECT  Menu_Id ,
        CASE WHEN b.Menu_Id IS NOT NULL THEN '存在'
             ELSE '不存在'
        END d
FROM    cy_bt_Menu_Info a
        LEFT JOIN ( SELECT  Menu_Id
                    FROM    cy_bt_Menu_Unit
                    WHERE   ( Menu_Id = 'Menu_Id' )
                  ) b ON a.menu_id = b.menu_id

[其他解释]

SELECT  a.Menu_Id ,
        CASE WHEN b.Menu_Id IS NULL THEN '不存在'
             ELSE '存在'
        END AS d
FROM    cy_bt_Menu_Info a
        LEFT JOIN ( SELECT  Menu_Id
                    FROM    cy_bt_Menu_Unit
                    WHERE   ( Menu_Id = 'Menu_Id' )
                  ) b ON a.Menu_Id = b.Menu_Id

[其他解释]
要用case when EXISTS(SELECT 1 FROM cy_bt_Menu_Unit WHERE Menu_Id = a.Menu_Id) then '存在' ELSE '不存在' end
if else是不合法的