mysql - レコードがmysqlに存在しない場合のチェックを作成する方法は?

Question

こんにちは、次のクエリで郡を表示したいのですが、郡が存在しない場合は、代わりに都市を返します。

        SELECT P.id  AS id, SUM(P.price)  AS price, 
                    P.tax, 
                    county  
                FROM Purchases AS  P
                JOIN Status  AS S       ON S.id = T.status_id
                JOIN Shipping AS Ship   ON S.shipping_id= Ship.id
                JOIN Shipping_Addresses AS  SA      ON Ship.shipping_address_id = SA.id
                JOIN Zip_Codes          AS ZIP      ON ZIP.zip_code = SA.zip_code
                JOIN Counties           AS C        ON ZIP.city = C.city
                JOIN States             AS STATE    ON STATE.id = C.county_state_id

                GROUP BY ZIP.zip_code
                ORDER BY county

ありがとう

Answer 1

使ってみてくださいCOALESCE():

COALESCE(county, city) AS location

countyの場合、代わりNULLに の値を返しますcity。

そう：

SELECT P.id  AS id, SUM(P.price)  AS price, 
    P.tax, 
    COALESCE(county, city) AS location