Question

我有两个桌子。

表A具有一个唯一的keyid列和一个标识个人的uid列。每个uid都有多个行。

表B与表A相同，但表A中没有其他所有列。

我将创建一个表C，其中包含表A和表B的所有信息

我想要的是一个查询，该查询针对每个uid接受来自Tabla A的最高keyid和来自表B的最高keyid，并插入到表C中。

如何编写这样的查询？

编辑：这是两个表以及我想要的示例

TABLE A
keyid | uid | name | likes
-----------------------------
  1     15    John   nothing
  2     15    John   something
  3     32    Jane   or other

TABLE B
keyid | uid | fruit | 
-----------------------------
  1     15    oranges
  2     32    banana
  3     32    apple


TABLE C (resulting query)
uid | name | likes     | fruit
-------------------------------
 15   John   something   oranges
 32   Jane   or other    apple

Answer 1

对于MySQL或其他支持row_number（）over（）的数据库的替代方法

merge(A, merge(B, C))

CREATE TABLE TableA(
   keyid  INTEGER  NOT NULL PRIMARY KEY
  ,uid    INTEGER  NOT NULL
  ,name   VARCHAR(20)  NOT NULL
  ,likes  VARCHAR(40)  NOT NULL
);

INSERT INTO TableA(keyid,uid,name,likes) 
VALUES 
(1,15,'John','nothing'),
(2,15,'John','something'),
(3,32,'Jane','or other');

CREATE TABLE TableB(
   keyid  VARCHAR(30) NOT NULL PRIMARY KEY
  ,uid    INTEGER  NOT NULL
  ,fruit  VARCHAR(40)  NOT NULL
);

INSERT INTO TableB(keyid,uid,fruit)
VALUES 
(1,15,'oranges'),
(2,32,'banana'),
(3,32,'apple');

uid | name | likes     | fruit  
--: | :--- | :-------- | :------
 15 | John | something | oranges
 32 | Jane | or other  | apple

db <>提琴here

Answer 2

您可以使用CREATE TABLE ... SELECT查询，从每个表中选择uid对应于keyid的最大值为uid的表中的值：

CREATE TABLE TableC AS
SELECT a.uid, a.name, a.likes, b.fruit
FROM (SELECT * 
      FROM TableA a
      WHERE a.keyid = (SELECT MAX(keyid) FROM TableA a2 WHERE a2.uid = a.uid)) a
JOIN (SELECT * 
      FROM TableB b
      WHERE b.keyid = (SELECT MAX(keyid) FROM TableB b2 WHERE b2.uid = b.uid)) b ON b.uid = a.uid

输出（用于您的示例数据）：

uid     name    likes       fruit
15      John    something   oranges
32      Jane    or other    apple

Demo on dbfiddle

更新

要将自动增量ID列添加到表中，只需在查询的CREATE TABLE部分中将其指定为列即可：

CREATE TABLE TableC (keyid INT UNSIGNED AUTO_INCREMENT PRIMARY KEY) AS
SELECT a.uid, a.name, a.likes, b.fruit
FROM (SELECT * 
      FROM TableA a
      WHERE a.keyid = (SELECT MAX(keyid) FROM TableA a2 WHERE a2.uid = a.uid)) a
JOIN (SELECT * 
      FROM TableB b
      WHERE b.keyid = (SELECT MAX(keyid) FROM TableB b2 WHERE b2.uid = b.uid)) b ON b.uid = a.uid

输出：

keyid   uid     name    likes       fruit
1       15      John    something   oranges
2       32      Jane    or other    apple

使用每个表的最高ID将两个表中的信息合并为一个

2 个答案: