MySql:如果值存在，则更新否则插入
MySql:如果值存在，则更新否则插入
提问于 2012-04-11 04:06:07
我有一些代码，看起来像这样。表中还有一个我必须保留的自动增量字段(它在其他表中使用)。我想简化和优化这段代码。
$query ="SELECT * FROM models WHERE col1 = 'foo'";
$testResult = mysql_query($query) or die('Error, query failed');
if(mysql_fetch_array($testResult) == NULL){
//insert...
$query ="INSERT INTO models (col1, col2, col3)
VALUES ('foo', 'bar', 'alph')";
$result = mysql_query($query) or die('Error, query failed');
}else{
//update...
$query = "UPDATE models
SET col1='foo', col2='bar', col3='alph'
WHERE col1='foo' AND col2='bar'";
$result = mysql_query($query) or die('Error, query failed');
}编辑:主键id是自动递增的字段。我从来不想改变这一点。但是，当另一个字段重复时，这是我想要更新该记录的时候。
回答 4
Stack Overflow用户
回答已采纳
发布于 2012-04-11 04:13:34
替换为：
REPLACE INTO models
( col1, col2, col3 )
VALUES
( 'foo', 'bar', 'alpha' )假设col1是您的主键，如果值为'foo‘的行已经存在，它将更新其他两列。否则，它将插入一个新行。
Stack Overflow用户
发布于 2012-04-11 04:08:54
您可以尝试使用“INSERT ... ON DUPLICATE KEY UPDATE”语法
http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that would cause a duplicate value in a UNIQUE index or PRIMARY KEY, an UPDATE of the old row is performed. For example, if column a is declared as UNIQUE and contains the value 1, the following two statements have identical effect:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=c+1;
UPDATE table SET c=c+1 WHERE a=1;
The ON DUPLICATE KEY UPDATE clause can contain multiple column assignments, separated by commas.
With ON DUPLICATE KEY UPDATE, the affected-rows value per row is 1 if the row is inserted as a new row and 2 if an existing row is updated.
If column b is also unique, the INSERT is equivalent to this UPDATE statement instead:
UPDATE table SET c=c+1 WHERE a=1 OR b=2 LIMIT 1;
If a=1 OR b=2 matches several rows, only one row is updated. In general, you should try to avoid using an ON DUPLICATE KEY clause on tables with multiple unique indexes.
You can use the VALUES(col_name) function in the UPDATE clause to refer to column values from the INSERT portion of the INSERT ... UPDATE statement. In other words, VALUES(col_name) in the UPDATE clause refers to the value of col_name that would be inserted, had no duplicate-key conflict occurred. This function is especially useful in multiple-row inserts. The VALUES() function is meaningful only in INSERT ... UPDATE statements and returns NULL otherwise. Example:
INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6)
ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b);
That statement is identical to the following two statements:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=3;
INSERT INTO table (a,b,c) VALUES (4,5,6)
ON DUPLICATE KEY UPDATE c=9;
If a table contains an AUTO_INCREMENT column and INSERT ... UPDATE inserts a row, the LAST_INSERT_ID() function returns the AUTO_INCREMENT value. If the statement updates a row instead, LAST_INSERT_ID() is not meaningful. However, you can work around this by using LAST_INSERT_ID(expr). Suppose that id is the AUTO_INCREMENT column. To make LAST_INSERT_ID() meaningful for updates, insert rows as follows:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), c=3;
The DELAYED option is ignored when you use ON DUPLICATE KEY UPDATE.Stack Overflow用户
发布于 2012-04-11 04:15:19
只需在副本上更新col3即可。这正是您所要求的。
INSERT INTO models (col1, col2, col3)
VALUES ('foo', 'bar', 'alpha')
ON DUPLICATE KEY UPDATE col3='alpha';页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/10095680
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