Question

我有结构表 prod ID，姓名，关键字，年长。

有必要在年生字段中显示遇到的关键字数量，例如

SELECT yearborn, COUNT(Id) cnt1 FROM prod WHERE keyword='admiral'
GROUP BY yearborn

和

SELECT yearborn, COUNT(Id) cnt2 FROM prod WHERE keyword='captain' GROUP BY yearborn

如何组合这两个查询以获取具有结构

的输出结果表

年长，cnt1，cnt2 ？

我试过UNION

SELECT yearborn, COUNT(Id) cnt1 FROM prod WHERE keyword='admiral' GROUP BY yearborn
UNION
SELECT yearborn, COUNT(Id) cnt2 FROM prod WHERE keyword='captain' GROUP BY yearborn

但结果是： 年长，cnt1

请告诉我如何摆脱这种情况。

Answer 1

您可以在关键字条件上使用SUM（）来执行此操作，因为MySQL中的比较结果可以视为0（false）或1（true）：

SELECT yearborn, SUM(keyword='admiral') cnt1, SUM(keyword='captain') cnt2 FROM prod GROUP BY yearborn

这也具有仅使用一次表扫描的优势（它比使用联合和子查询更快）。

Answer 2

  SELECT yearborn, 
         SUM(IF(keyword = 'admiral', 1, 0)) cnt1, 
         SUM(IF(keyword = 'captain', 1, 0)) cnt2 
    FROM prod 
   WHERE keyword = 'admiral'
      OR keyword = 'captain'
GROUP BY yearborn

结果将是这样的（当然这是虚构的数据）：

+----------+------+------+
| yearborn | cnt1 | cnt2 |
+----------+------+------+
|     2004 | 1233 |    0 |
|     1999 |    0 |   15 |
+----------+------+------+

Answer 3

SELECT yearborn, COUNT(Id) cnt1, NULL cnt2 FROM prod WHERE keyword='admiral' GROUP BY yearborn
UNION
SELECT yearborn, NULL cnt1, COUNT(Id) cnt2 FROM prod WHERE keyword='captain' GROUP BY yearborn

Answer 4

怎么样：

SELECT yearborn,SUM(cnt1),SUM(cnt2) FROM
( 
    SELECT yearborn, COUNT(id) cnt1, 0 cnt2 FROM prod WHERE keyword='admiral' 
    UNION ALL 
    SELECT yearborn, 0 cnt1, COUNT(id) cnt2 FROM prod WHERE keyword='captain'
) 
GROUP BY yearborn

Answer 5

嗯，你可以试试这个：

SELECT `yearborn`,
COUNT(`Id`) AS `cnt1`
FROM `prod`
WHERE `keyword` IN ('admiral','captain')
GROUP BY `yearborn`,`keyword`;

编辑：在GROUP BY语句中添加了keyword。

两个My SQL查询的问题

5 个答案: