Question

我有桌子

表1

id text
1   A
1   B
2   C

表2

id text
1  x
1  f  
2  y
2  z

我想以这种方式加入他们

1 A x
1 B f
2 C y
2   z

换句话说，我希望看到table1和table2中的所有文本按id分组，没有重复。有什么想法吗？

更新：正如他们在评论中所说，逻辑不明确，我会尝试解释。我在table_1中有当前值，在table_2中删除了值。客户希望在一个表中按当前ID分组查看当前值和已删除的值。

Answer 1

简单的解决方案，以获得接近您正在寻找的东西

SELECT t1.id, t1.text, t2.text
FROM tbl_1 t1
  INNER JOIN tbl_2 t2
    ON t1.id = t2.id

这将创建输出

1 A x
1 B x
2 C y
2 C z

现在唯一不同的是，重复文本x和C应该以某种方式删除。

<强>更新 前提条件：每个ID的重复项都在tbl_1或tbl_2中，而不是两者都有！

除上述简单解决方案外，加入分组选择将允许创建一种“CASE-Filters”以获得所需的输出。

SELECT
  t1.id,
  CASE
    WHEN t2.text = txt_i2 THEN t1.text
  END AS txt_t1,
  CASE
    WHEN t1.text = txt_i1 THEN t2.text
  END AS txt_t2
FROM (
    SELECT
      i1.id,
      i1.text AS txt_i1,
      i2.text AS txt_i2
    FROM tbl_1 i1
      INNER JOIN tbl_2 i2
        ON i1.id = i2.id
    GROUP BY id
  ) i
  INNER JOIN tbl_1 t1
    ON i.id = t1.id
  INNER JOIN tbl_2 t2
    ON t1.id = t2.id

您应该创建tbl_1-tbl_2-join的视图以获得更具可读性的SQL：

CREATE OR REPLACE VIEW V_tbl_1_2 AS (
SELECT 
  t1.id,
  t1.text AS txt_1,
  t2.text AS txt_2
FROM tbl_1 t1
  INNER JOIN tbl_2 t2
    ON t1.id = t2.id
)
;

SELECT
  t.id,
  CASE
    WHEN t.txt_2 = i.txt_2 THEN t.txt_1
  END AS txt_t1,
  CASE
    WHEN t.txt_1 = i.txt_1 THEN t.txt_2
  END AS txt_t2
FROM V_tbl_1_2 t
  INNER JOIN (
    SELECT *
    FROM V_tbl_1_2
    GROUP BY id
  ) i ON t.id = i.id
;

Answer 2

使用MYSQL VIEW或JOIN

Answer 3

如果两个表中每个id的项目不超过两个，并且两者都没有完全重复，则此方法有效。（而且我还必须补充一点，这只有在MySQL能够吞下这个怪物并且不会被它窒息的情况下才有效。）

SELECT
  COALESCE (t1.id, t2.id) AS id,
  t1.text AS text1,
  t2.text AS text2
FROM (
  SELECT
    t.id,
    t.text,
    CASE t.text WHEN m.text THEN 1 ELSE 2 END AS rowid
  FROM table_1 t
    INNER JOIN (
      SELECT id, MIN(text) AS text
      FROM table_1
      GROUP BY id
    ) m ON t.id = m.id
) t1
FULL JOIN (
  SELECT
    t.id,
    t.text,
    CASE t.text WHEN m.text THEN 1 ELSE 2 END AS rowid
  FROM table_2 t
    INNER JOIN (
      SELECT id, MIN(text) AS text
      FROM table_2
      GROUP BY id
    ) m ON t.id = m.id
) t2
ON t1.id = t2.id AND t1.rowid = t2.rowid
ORDER BY COALESCE (t1.id, t2.id), COALESCE (t1.rowid, t2.rowid)

sql查询问题

3 个答案: