Question

我有一张桌子，其中包含两队之间足球比赛的结果。首先，我想要一个团队的下拉菜单。这应该只是SELECT * FROM table GROUP BY Team_A

但如果团队只出现在Team_B专栏中，他们可能会错过。是否可以对列Team_A和Team_B进行分组，以便我可以在两列中输出所有唯一的团队？

Answer 1

如果您想要所有名称，请使用union。这也消除了重复：

select TeamA from table union
select TeamB from table

Answer 2

这将为您提供正确的数据，但是。。

select team_a as team_name
from test
union
select team_b
from test
order by team_name;

您可能应该对团队表进行外键引用。如果您有那个，并且对团队名称有强制性的唯一约束，那么您只需要

select team_name
from teams
order by team_name;

Answer 3

你不只是意味着：

group by Team_A, Team_B

这将按Team_A和Team_B

的组合进行分组

编辑：最终得到两个列，每个列都有一个唯一的列表，这些列已经存在于该列中（完全如OP所述）：

SELECT a.*, b.* FROM
(SELECT Team_A, @ida := ifnull(@ida,0) + 1 AS ida FROM table GROUP BY Team_A) AS a
LEFT JOIN
(SELECT Team_B, @idb := ifnull(@idb,0) + 1 AS idb FROM table GROUP BY Team_B) AS b
ON a.ida=b.idb
and isnull(@ida := null) and isnull(@idb := null) -- reset @ida and @idb

UNION ALL -- turn the left and right join into full outer join

SELECT c.*, d.* FROM
(SELECT Team_A, @idc := ifnull(@idc,0) + 1 AS idc FROM table GROUP BY Team_A) AS c
RIGHT JOIN
(SELECT Team_B, @idd := ifnull(@idd,0) + 1 AS idd FROM table GROUP BY Team_B) AS d
ON c.idc=d.idd
and isnull(@idc := null) and isnull(@idd := null) -- reset @idc and @idd
WHERE c.idc is null -- prevent doubles in the full outer join

Answer 4

像这样使用UNION：

SELECT Team_A AS TeamName FROM table
UNION ALL
SELECT Team_B AS TeamName FROM table

获取不同的团队列表。但我不得不说，真的需要重组数据库。你应该有这样一个表：

CREATE TABLE Teams (
    ID INT PRIMARY KEY IDENTITY(1, 1),
    Name VARCHAR(50) NOT NULL UNIQUE
)

然后是这样的表：

CREATE TABLE Scores (
    ID INT PRIMARY KEY IDENTITY(1, 1),
    HomeTeamId INT NOT NULL,
    AwayTeamId INT NOT NULL,
    HomeTeamScore INT NOT NULL,
    AwayTeamScore INT NOT NULL
)

这样不仅可以更直接地选择团队：

SELECT Name FROM Teams

但它也会构建一些真正的数据库完整性，因为您可以构建外键，并且不会使用简单的字符串值来指示键值。

复杂的MySQL组

4 个答案: