Question

我有一张桌子

Sport    Name   gender
----------------------
tennis   John     M
football David    M
football Jane     F
football Brad     M

我希望的结果就像

Count Sport Gender
1      Tennis  M
0      tennis  F
2      football M
1      football F

到目前为止，我可以得到像

Count Sport Gender
4      Tennis  M
4      tennis  F
4      football M
4      football F

或者我只计算网球和男性等1个条件。

我已经阅读了聚合函数，但我仍然无法实现。我无法想出解决方案来单独计算。

Answer 1

以下是一种方式，CROSS JOIN + LEFT OUTER JOIN + COUNT

SELECT a.sport,
       b.gender,
       Count(c.sport) AS count
FROM   (SELECT DISTINCT sport
        FROM   yourtable) a
       CROSS JOIN (SELECT 'M' AS Gender
                   UNION ALL
                   SELECT 'F') b
       LEFT OUTER JOIN yourtable c
                    ON a.sport = c.sport
                       AND b.gender = c.gender
GROUP  BY a.sport,
          b.gender

<强>演示：

表架构＆amp;数据

CREATE TABLE yourtable
  (
     Sport  VARCHAR(50),
     NAME   VARCHAR(50),
     gender CHAR(1)
  );

INSERT INTO yourtable VALUES ('tennis','John','M' );
INSERT INTO yourtable VALUES ('football','David','M' );
INSERT INTO yourtable VALUES ('football','Jane','F' );
INSERT INTO yourtable VALUES ('football','Brad','M' );

<强>结果

╔══════════╦════════╦═══════╗
║  sport   ║ gender ║ count ║
╠══════════╬════════╬═══════╣
║ football ║ M      ║     2 ║
║ football ║ F      ║     1 ║
║ tennis   ║ M      ║     1 ║
║ tennis   ║ F      ║     0 ║
╚══════════╩════════╩═══════╝

这里的关键是，由于您希望能够获得0个计数，因此您需要CROSS JOIN才能获得所有可能的组合，即使表中没有符合该条件的行（例如，没有女网球运动员的行。）

来自行

1 个答案: