《MYSQL教程MYSQL插入處理重復鍵值的幾種方法》要點：
本文介紹了MYSQL教程MYSQL插入處理重復鍵值的幾種方法，希望對您有用。如果有疑問，可以聯系我們。

先建立2個測試表,在id列上創建unique約束.
mysql> create table test1(id int,name varchar(5),type int,primary key(id));
Query OK, 0 rows affected (0.01 sec)
mysql> create table test2(id int,name varchar(5),type int,primary key(id));
Query OK, 0 rows affected (0.01 sec)
mysql> select * from test1;
+-----+------+------+
| id? | name | type |
+-----+------+------+
| 101 | aaa? |??? 1 |
| 102 | bbb? |??? 2 |
| 103 | ccc? |??? 3 |
+-----+------+------+
3 rows in set (0.00 sec)
mysql> select * from test2;
+-----+------+------+
| id? | name | type |
+-----+------+------+
| 201 | aaa? |??? 1 |
| 202 | bbb? |??? 2 |
| 203 | ccc? |??? 3 |
| 101 | xxx? |??? 5 |
+-----+------+------+
4 rows in set (0.00 sec)
1、REPLACE INTO
發現重復的先刪除再插入,如果記錄有多個字段,在插入的時候如果有的字段沒有賦值,那么新插入的記錄這些字段為空.
mysql> replace into test1(id,name)(select id,name from test2);
Query OK, 5 rows affected (0.04 sec)
Records: 4? Duplicates: 1? Warnings: 0
mysql> select * from test1;
+-----+------+------+
| id? | name | type |
+-----+------+------+
| 101 | xxx? | NULL |
| 102 | bbb? |??? 2 |
| 103 | ccc? |??? 3 |
| 201 | aaa? | NULL |
| 202 | bbb? | NULL |
| 203 | ccc? | NULL |
+-----+------+------+
6 rows in set (0.00 sec)
需要注意的是,當你replace的時候,如果被插入的表如果沒有指定列,會用NULL表示,而不是這個表原來的內容.如果插入的內容列和被插入的表列一樣,則不會出現NULL.例如
mysql> replace into test1(id,name,type)(select id,name,type from test2);
Query OK, 8 rows affected (0.04 sec)
Records: 4? Duplicates: 4? Warnings: 0
mysql> select * from test1;
+-----+------+------+
| id? | name | type |
+-----+------+------+
| 101 | xxx? |??? 5 |
| 102 | bbb? |??? 2 |
| 103 | ccc? |??? 3 |
| 201 | aaa? |??? 1 |
| 202 | bbb? |??? 2 |
| 203 | ccc? |??? 3 |
+-----+------+------+
6 rows in set (0.00 sec)
如果INSERT的時候,需要保留被插入表的列,只更新指定列,那么就可以使用第二種方法.
2、INSERT INTO ON DUPLICATE KEY UPDATE
發現重復的是更新操作.在原有記錄基礎上,更新指定字段內容,其它字段內容保留.例如我只想插入test2表的id,name字段,但是要保留test1表的type字段：
mysql> insert into test1(id,name,type)(select id,name,type from test2) on DUPLICATE KEY UPDATE test1.name=test2.name;
Query OK, 5 rows affected (0.04 sec)
Records: 4? Duplicates: 1? Warnings: 0
mysql> select * from test1;
+-----+------+------+
| id? | name | type |
+-----+------+------+
| 101 | xxx? |??? 1 |
| 102 | bbb? |??? 2 |
| 103 | ccc? |??? 3 |
| 203 | ccc? |??? 3 |
| 202 | bbb? |??? 2 |
| 201 | aaa? |??? 1 |
+-----+------+------+
6 rows in set (0.00 sec)
如果INSERT的時候,只想插入原表沒有的數據,那么可以使用第三種方法.
3、IGNORE INTO
判斷是否存在,存在不插入,否則插入.很容易理解,當插入的時候,違反唯一性約束,MySQL不會嘗試去執行這條語句.例如：
mysql> insert ignore into test1(id,name,type)(select id,name,type from test2);
Query OK, 3 rows affected (0.01 sec)
Records: 4? Duplicates: 1? Warnings: 0
mysql> select * from test1;
+-----+------+------+
| id? | name | type |
+-----+------+------+
| 101 | aaa? |??? 1 |
| 102 | bbb? |??? 2 |
| 103 | ccc? |??? 3 |
| 203 | ccc? |??? 3 |
| 202 | bbb? |??? 2 |
| 201 | aaa? |??? 1 |
+-----+------+------+
6 rows in set (0.00 sec)

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