MySql:如果值存在UPDATE,则INSERT

Question

我有一些看起来像这样的代码.表中还有一个我必须保留的自动增量字段(在其他表中使用).我想简化和优化此代码.

$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.我永远不想改变这一点.但是,当复制另一个字段时,这就是我想要更新该记录的时间.

Answer 1

REPLACE INTO怎么样:

REPLACE INTO models
( col1, col2, col3 )
VALUES
( 'foo', 'bar', 'alpha' )

假设col1是您的主键,如果已存在值为'foo'的行,则它将更新其他两列.否则它将插入一个新行.

Answer 2

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.

Answer 3

您只需要在复制时更新col3.这正是你要求的.

INSERT INTO models (col1, col2, col3)
VALUES ('foo', 'bar', 'alpha')
ON DUPLICATE KEY UPDATE col3='alpha';