如果可以接受异常，任何简单的约束都可以完成这项工作。例子:

如果不是代理则是主键 列上的唯一约束 多列唯一约束

如果这看起来很简单，我很抱歉。我知道面对你和我们分享的链接看起来很糟糕。, (

但我还是给出了这个答案，因为它似乎满足了你的需要。(如果不是，它可能会触发您更新您的需求，这也是“一件好事”(TM))。

如果插入会破坏数据库唯一约束，则在数据库级别抛出异常，由驱动程序转发。它肯定会因为失败而停止您的脚本。它必须有可能在PHP中解决这种情况…

INSERT INTO table_name (columns) VALUES (values) ON CONFLICT (id) DO NOTHING;

试试下面的方法:

IF (SELECT COUNT(*) FROM beta WHERE name = 'John' > 0)
  UPDATE alfa SET c1=(SELECT id FROM beta WHERE name = 'John')
ELSE
BEGIN
  INSERT INTO beta (name) VALUES ('John')
  INSERT INTO alfa (c1) VALUES (LAST_INSERT_ID())
END

下面是一个PHP函数，它只在表中不存在所有指定列的值时插入一行。

If one of the columns differ, the row will be added. If the table is empty, the row will be added. If a row exists where all the specified columns have the specified values, the row won't be added. function insert_unique($table, $vars) { if (count($vars)) { $table = mysql_real_escape_string($table); $vars = array_map('mysql_real_escape_string', $vars); $req = "INSERT INTO `$table` (`". join('`, `', array_keys($vars)) ."`) "; $req .= "SELECT '". join("', '", $vars) ."' FROM DUAL "; $req .= "WHERE NOT EXISTS (SELECT 1 FROM `$table` WHERE "; foreach ($vars AS $col => $val) $req .= "`$col`='$val' AND "; $req = substr($req, 0, -5) . ") LIMIT 1"; $res = mysql_query($req) OR die(); return mysql_insert_id(); } return False; }

使用示例:

<?php
  insert_unique('mytable', array(
    'mycolumn1' => 'myvalue1',
    'mycolumn2' => 'myvalue2',
    'mycolumn3' => 'myvalue3'
    )
  );
?>

使用INSERT IGNORE INTO表。

还有INSERT…ON DUPLICATE KEY UPDATE语法，你可以在13.2.6.2 INSERT…打开重复的键更新语句。

根据谷歌的webcache，帖子来自bogdan.org.ua:

18th October 2007 To start: as of the latest MySQL, syntax presented in the title is not possible. But there are several very easy ways to accomplish what is expected using existing functionality. There are 3 possible solutions: using INSERT IGNORE, REPLACE, or INSERT … ON DUPLICATE KEY UPDATE. Imagine we have a table: CREATE TABLE `transcripts` ( `ensembl_transcript_id` varchar(20) NOT NULL, `transcript_chrom_start` int(10) unsigned NOT NULL, `transcript_chrom_end` int(10) unsigned NOT NULL, PRIMARY KEY (`ensembl_transcript_id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; Now imagine that we have an automatic pipeline importing transcripts meta-data from Ensembl, and that due to various reasons the pipeline might be broken at any step of execution. Thus, we need to ensure two things:

反复执行的管道不会破坏我们的 >数据库

repeated executions will not die due to ‘duplicate > primary key’ errors. Method 1: using REPLACE It’s very simple: REPLACE INTO `transcripts` SET `ensembl_transcript_id` = 'ENSORGT00000000001', `transcript_chrom_start` = 12345, `transcript_chrom_end` = 12678; If the record exists, it will be overwritten; if it does not yet exist, it will be created. However, using this method isn’t efficient for our case: we do not need to overwrite existing records, it’s fine just to skip them. Method 2: using INSERT IGNORE Also very simple: INSERT IGNORE INTO `transcripts` SET `ensembl_transcript_id` = 'ENSORGT00000000001', `transcript_chrom_start` = 12345, `transcript_chrom_end` = 12678; Here, if the ‘ensembl_transcript_id’ is already present in the database, it will be silently skipped (ignored). (To be more precise, here’s a quote from MySQL reference manual: “If you use the IGNORE keyword, errors that occur while executing the INSERT statement are treated as warnings instead. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted.”.) If the record doesn’t yet exist, it will be created. This second method has several potential weaknesses, including non-abortion of the query in case any other problem occurs (see the manual). Thus it should be used if previously tested without the IGNORE keyword. Method 3: using INSERT … ON DUPLICATE KEY UPDATE: Third option is to use INSERT … ON DUPLICATE KEY UPDATE syntax, and in the UPDATE part just do nothing do some meaningless (empty) operation, like calculating 0+0 (Geoffray suggests doing the id=id assignment for the MySQL optimization engine to ignore this operation). Advantage of this method is that it only ignores duplicate key events, and still aborts on other errors. As a final notice: this post was inspired by Xaprb. I’d also advise to consult his other post on writing flexible SQL queries.

如果可以接受异常，任何简单的约束都可以完成这项工作。例子:

如果不是代理则是主键 列上的唯一约束 多列唯一约束

如果这看起来很简单，我很抱歉。我知道面对你和我们分享的链接看起来很糟糕。, (

但我还是给出了这个答案，因为它似乎满足了你的需要。(如果不是，它可能会触发您更新您的需求，这也是“一件好事”(TM))。

如果插入会破坏数据库唯一约束，则在数据库级别抛出异常，由驱动程序转发。它肯定会因为失败而停止您的脚本。它必须有可能在PHP中解决这种情况…