Question

如何从不同条件的相同字段返回2列，这是两个条件：

SELECT CITY,REGION,SALES FROM SALESREPS WHERE SALES < QUOTA;

SELECT CITY,REGION,SALES FROM SALESREPS WHERE SALES > QUOTA;

我的意思是说有些人说我只需要输入＆＃39; AND＆＃39;。那么我需要的是来自该示例的1行代码，它将返回2个不同的销售列。第一列将是销售额＆lt;配额和另一列是销售＆gt;配额。所有这些都来自同一张桌子。

Answer 1

您可以使用mySql if语句，如下所示：

SELECT 
    CITY,
    REGION,
    SALES,
    IF (SALES < QUOTA,SALES,null) as BELOW_QUOTA,
    IF (SALES > QUOTA,SALES,null) as ABOVE_QUOTA
    FROM SALESREPS;

Answer 2

SELECT CITY，REGION，IF（SALES＆lt; QUOTA，SALES）AS LessThanColumn，IF（Sales＆gt; QUOTA，Sales）AS GreaterThanColumn FROM SALESREPS

Answer 3

如果您只想要4列（CITY，REGION，LOW_SALES，HIGH_SALES），则每行只包含一个LOW_SALES和HIGH_SALES有一个值（另一个为null），那么你可以：

select CITY
     , REGION
     , case when SALES < QUOTA then SALES end as LOW_SALES
     , case when SALES > QUOTA then SALES end as HIGH_SALES
  from SALESREPS;

SQL语句使用数据库不可知的语法，因此它可以在除MySQL之外的数据库上工作。

这也可以使用union：

来完成

select CITY, REGION, SALES as LOW_SALES, null as HIGH_SALES
  from SALESREPS
 where SALES < QUOTA
union all
select CITY, REGION, null as LOW_SALES, SALES as HIGH_SALES
 from SALESREPS
 where SALES > QUOTA;

对我来说没有任何意义，例如那些有SALES = QUOTA的行？

现在，如果您想要CITY / REGION的总计，那对我来说更有意义（包括HIGH_SALES中的完全相等）：

select CITY
     , REGION
     , sum(case when SALES < QUOTA then SALES else 0 end) as LOW_SALES
     , sum(case when SALES >= QUOTA then SALES else 0 end) as HIGH_SALES
  from SALESREPS
 group by CITY
        , REGION;

如果您只想要计数：

select CITY
     , REGION
     , sum(case when SALES < QUOTA then 1 else 0 end) as LOW_SALES
     , sum(case when SALES >= QUOTA then 1 else 0 end) as HIGH_SALES
  from SALESREPS
 group by CITY
        , REGION;

mysql从同一个字段返回2个不同的列，但具有不同的条件

3 个答案: