Question

我在PostgreSQL 9.3.1模式的http://sqlfiddle.com上创建了下表：

CREATE TABLE t
(
  id serial primary key,
  m varchar(1),
  d varchar(1),
  c int
);

INSERT INTO t
(m, d, c)
VALUES
('A', '1', 101),
('A', '2', 102),
('A', '3', 103),
('B', '1', 104),
('B', '3', 105);

表：

| ID | M | D |   C |
|----|---|---|-----|
|  1 | A | 1 | 101 |
|  2 | A | 2 | 102 |
|  3 | A | 3 | 103 |
|  4 | B | 1 | 104 |
|  5 | B | 3 | 105 |

从此我想生成这样一个表：

| M | D |     ID |      C |
|---|---|--------|--------|
| A | 1 |      1 |    101 |
| A | 2 |      2 |    102 |
| A | 3 |      3 |    103 |
| B | 1 |      4 |    104 |
| B | 2 | (null) | (null) |
| B | 3 |      5 |    105 |

但是我当前的陈述

select * from
  (select * from
    (select distinct m from t) as dummy1,
    (select distinct d from t) as dummy2) as combi
  full outer join
    t
  on combi.d = t.d and combi.m = t.m

我只得到以下

| M | D |     ID |      C |
|---|---|--------|--------|
| A | 1 |      1 |    101 |
| B | 1 |      4 |    104 |
| A | 2 |      2 |    102 |
| A | 3 |      3 |    103 |
| B | 3 |      5 |    105 |
| B | 2 | (null) | (null) |

尝试按m进行订购，到目前为止失败：

select * from
  (select * from
    (select * from
      (select * from
        (select distinct m from t) as dummy1,
        (select distinct d from t) as dummy2) as kombi
      full outer join
        t
      on kombi.d = t.d and kombi.m = t.m) as result)
order by result.m

错误讯息：

ERROR: subquery in FROM must have an alias: select * from (select * from (select * from (select * from (select distinct m from t) as dummy1, (select distinct d from t) as dummy2) as kombi full outer join t on kombi.d = t.d and kombi.m = t.m) as result) order by result.m

如果有人可以向我指出我做错了什么并且可能显示正确的陈述，那将会很酷。

Answer 1

select * from
  (select kombi.m, kombi.d, t.id, t.c from
    (select * from
      (select distinct m from t) as dummy1,
      (select distinct d from t) as dummy2) as kombi
     full outer join t
  on kombi.d = t.d and kombi.m = t.m) as result
order by result.m, result.d

Answer 2

我认为你的问题是订单。您可以使用order by子句解决此问题：

select * from
  (select * from
    (select distinct m from t) as dummy1,
    (select distinct d from t) as dummy2) as combi
  full outer join
    t
  on combi.d = t.d and combi.m = t.m
order by combi.m, combi.d

您需要指定要订购的数据。在这种情况下，你从组合表中取回行，所以你需要这样说。 http://sqlfiddle.com/#!15/ddc0e/17

Answer 3

您也可以使用列号而不是名称来进行排序。

select * from
  (select * from
    (select distinct m from t) as dummy1,
    (select distinct d from t) as dummy2) as combi
  full outer join
    t
  on combi.d = t.d and combi.m = t.m
order by 1,2;

| M | D |     ID |      C |
|---|---|--------|--------|
| A | 1 |      1 |    101 |
| A | 2 |      2 |    102 |
| A | 3 |      3 |    103 |
| B | 1 |      4 |    104 |
| B | 2 | (null) | (null) |
| B | 3 |      5 |    105 |

Answer 4

你只需要一个数据透视表

查询非常简单

select classes.M, p.i as D, t.ID, t.C
from (select M, max(D) MaxValue from t group by m) classes
inner join pivot p
on p.i =< classes.MaxValue
left join t
on t.M = classes.M
and t.D = p.i

数据透视表是一个虚拟表的一些如何

CREATE TABLE Pivot (
 i INT,
 PRIMARY KEY(i)
)

填充是一些如何

CREATE TABLE Foo(
i CHAR(1)
)

INSERT INTO Foo VALUES('0')
INSERT INTO Foo VALUES('1')
INSERT INTO Foo VALUES('2')
INSERT INTO Foo VALUES('3')
INSERT INTO Foo VALUES('4')
INSERT INTO Foo VALUES('5')
INSERT INTO Foo VALUES('6')
INSERT INTO Foo VALUES('7')
INSERT INTO Foo VALUES('8')
INSERT INTO Foo VALUES('9')

使用Foo表中的10行，您可以轻松地使用1,000行填充数据透视表。要从10行获得1,000行，请将Foo连接到自身三次以创建笛卡尔积：

INSERT INTO Pivot
SELECT f1.i+f2.i+f3.i
FROM Foo f1, Foo F2, Foo f3

你可以在Jonathan Gennick，Ales Spetic的Transac-SQL Cookbook中读到这些内容

Answer 5

您只需按最终列定义排序即可。 t.m和t.d。所以你的最终SQL将是......

SELECT * 
FROM   (SELECT * 
        FROM   (SELECT DISTINCT m FROM   t) AS dummy1, 
               (SELECT DISTINCT d FROM   t) AS dummy2) AS combi 
       FULL OUTER JOIN t 
                    ON combi.d = t.d 
                       AND combi.m = t.m 
ORDER  BY t.m, 
          t.d;

同样对于查询优化透视图，现在最好有多层子查询。

Answer 6

我认为你需要另一个相关名称 - dummy3？ - 在“结果”之后，在订单之前。

完全外连接后的顺序

6 个答案: