Question

我试图以下列方式选择一些数据：

SELECT column
FROM table
WHERE a = a1
AND (b = b1 OR b = b2 OR b = b3);

我想要它做的是如果b不等于b1，检查b = b2。但是，如果b = b1，请不要检查其他条件。此select语句的结果必须只是一个条目。但是，在我没有的语句中，它会检查所有这三个条件，有时会返回多行。同样，我希望它停止检查条件是否为真。

有关如何实施的任何想法？我尝试了案例，但没有成功......

提前谢谢！

EDIT 这是我想要运行的实际查询。

INSERT INTO shipment_flights 
    (airlinename, flt_no, flt_date, destination, phone, depttime, arrivaltime, pcs, weight)
SELECT st.airlinename, flightno, flightdate, destination,     
(SELECT phone 
FROM carrierlocations 
WHERE carriers_carrierid = (select carrierid from carriers where airlinename = st.airlinename) 
AND (city = destination OR (city != destination AND
    city = (SELECT city FROM airports WHERE iataid = 
            (SELECT airports_iataid FROM ratelegs 
                WHERE shipments_shipid = c.shipments_shipid))
                ))) phone, 
depttime, arrivaltime, sum(linepcs), sum(lineweight)
FROM segment_times st
    JOIN contents2flights c2f 
        ON st.flightid = c2f.segments_flights_flightid 
        AND st.segmentid = c2f.segments_segmentid 
    JOIN contents c 
        ON c.lineno = c2f.contents_lineno 
        AND c.shipments_shipid = c2f.contents_shipments_shipid

WHERE c.shipments_shipid = var_shipid
GROUP BY flightid
ORDER BY flightdate, depttime;

以下是示例输出：

airlinename         flt_no  flt_date        destination    phone         pcs   weight
Everts Air Alaska   CH1     2008-02-20      Hughes         9074502351    24    2121

查询将一堆航班数据插入临时表。我遇到的问题是获取某个地点的电话号码。这部分内容如下：

(SELECT phone 
FROM carrierlocations 
WHERE carriers_carrierid = (select carrierid from carriers where airlinename = st.airlinename) 
AND (city = destination OR (city != destination AND
    city = (SELECT city FROM airports WHERE iataid = 
            (SELECT airports_iataid FROM ratelegs 
                WHERE shipments_shipid = c.shipments_shipid))))) phone

在Amit Bhargava建议的查询中，只有临时表中有一行时才会得到正确的结果。如果还有更多，则会在选择手机部分时抛出错误。

“错误代码：1242。子查询返回超过1行”

Answer 1

通过使用IF（）+ IF（）+ IF（），并且测试sum = 1可以防止大量额外的而不是其他标准。如果2或全部3相同，则总和将大于1.如果它们都不匹配，则结果为0.这应该完全符合您的要求。

SELECT column
  FROM table
  WHERE a = a1
    AND  if( b = b1, 1, 0 )
       + if( b = b2, 1, 0 )
       + if( b = b3, 1, 0 ) = 1

或者......在ypercube的帮助下，我一直忘记逻辑测试分别返回1或0表示真/假，例如......

SELECT column
  FROM table
  WHERE a = a1
    AND  (b = b1) + (b = b2) + (b = b3) = 1

Answer 2

请尝试以下方法。不是最优雅的解决方案，但它应该有效。

SELECT column
FROM table
WHERE a = a1
AND (b = b1 OR (b != b1 AND (b = b2 OR (b != b2 AND b = b3))))

MySQL存储过程：IF在WHERE中

2 个答案: