Question

我正在尝试将行从tableA复制到空白tableB。

tableA有一列mytext，这些行与此列有重复。

问题如何从A复制到B，而mytext没有重复的行？换句话说，如果mytext中有2个或更多行具有相同的值，请保留ID值最低的行并复制到tableB。

最初我试图删除重复项但却一直出现错误Error Code: 1205. Lock wait timeout exceeded from this sql command:

DELETE n1 
FROM tableA n1, tableA n2 
WHERE n1.id > n2.id 
AND n1.mytext = n2.mytext

我正在amazons RDS

+---+-----+-----+------+-------+
|id |fname|lname|mytext|morevar|
|---|-----|-----|------|-------|
|   |     |     |      |       |
|   |     |     |      |       |
|   |     |     |      |       |
|   |     |     |      |       |
+------------------------------+ 
CREATE TABLE `tableB` (
    `id` int(11) NOT NULL,
    `fname` varchar(45) DEFAULT NULL,
    `lname` varchar(45) DEFAULT NULL,
    `mytext` mediumtext,
    `morevar` bigint(20) DEFAULT NULL,
    PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$

这不起作用，它没有捕获重复项，只是将tableA中的所有值复制到tableB

INSERT INTO tableB (`id`,`fname`,`lname`,`mytext`,`morevar`)
SELECT DISTINCT tableA.id,tableA.fname,tableA.lname,tableA.mytext,tableA.morevar
FROM tableA

Answer 1

试试这个

INSERT INTO tableB (`id`,`fname`,`lname`,`mytext`,`morevar`)
SELECT id, fname, lname, mytext, morevar
FROM tableA a
WHERE id = (Select Min(id) FROM tableA
            WHERE myText = a.mytext)

如果您需要批量执行此操作...（编辑myText条件以控制批次）

INSERT INTO tableB (`id`,`fname`,`lname`,`mytext`,`morevar`)
SELECT id, fname, lname, mytext, morevar
FROM tableA a
WHERE mytext < 'j'
   And id = (Select Min(id) FROM tableA
            WHERE myText = a.mytext)

INSERT INTO tableB (`id`,`fname`,`lname`,`mytext`,`morevar`)
SELECT id, fname, lname, mytext, morevar
FROM tableA a
WHERE mytext >= 'j'
   And mytext < 'r'
   And id = (Select Min(id) FROM tableA
            WHERE myText = a.mytext)

INSERT INTO tableB (`id`,`fname`,`lname`,`mytext`,`morevar`)
SELECT id, fname, lname, mytext, morevar
FROM tableA a
WHERE mytext >= 'r'
   And id = (Select Min(id) FROM tableA
            WHERE myText = a.mytext)

Answer 2

您可以使用GROUP BY mytext将重复的行组合在一起。以下应该有效：

INSERT INTO tableB
SELECT * FROM tableA
  WHERE id IN (SELECT MIN(id) FROM tableA GROUP BY mytext)

如果A中的列不重复，则将tableA复制到tableB

2 个答案: