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copied!<p>use <code>INSERT IGNORE INTO table</code></p> <p>see <a href="http://bogdan.org.ua/2007/10/18/mysql-insert-if-not-exists-syntax.html" rel="noreferrer">http://bogdan.org.ua/2007/10/18/mysql-insert-if-not-exists-syntax.html</a></p> <p>there's also <code>INSERT … ON DUPLICATE KEY UPDATE</code> syntax, you can find explanations on <a href="http://dev.mysql.com/doc/refman/5.1/en/insert-on-duplicate.html" rel="noreferrer">dev.mysql.com</a></p> <hr> <p><strong>Post from bogdan.org.ua according to <a href="http://webcache.googleusercontent.com/search?q=cache:bogdan.org.ua/2007/10/18/mysql-insert-if-not-exists-syntax.html" rel="noreferrer">Google's webcache</a>:</strong></p> <blockquote> <p>18th October 2007</p> <p>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.</p> <p>There are 3 possible solutions: using INSERT IGNORE, REPLACE, or INSERT … ON DUPLICATE KEY UPDATE.</p> <p>Imagine we have a table:</p> <pre><code>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; </code></pre> <p>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: 1) repeated executions of the pipeline will not destroy our database, and 2) repeated executions will not die due to ‘duplicate primary key’ errors.</p> <p>Method 1: using REPLACE</p> <p>It’s very simple:</p> <pre><code>REPLACE INTO `transcripts` SET `ensembl_transcript_id` = ‘ENSORGT00000000001′, `transcript_chrom_start` = 12345, `transcript_chrom_end` = 12678; </code></pre> <p>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.</p> <p>Method 2: using INSERT IGNORE Also very simple:</p> <pre><code>INSERT IGNORE INTO `transcripts` SET `ensembl_transcript_id` = ‘ENSORGT00000000001′, `transcript_chrom_start` = 12345, `transcript_chrom_end` = 12678; </code></pre> <p>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.</p> <p>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.</p> <p>There is one more option: 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.</p> <p>As a final notice: this post was inspired by Xaprb. I’d also advise to consult his other post on writing flexible SQL queries.</p> </blockquote>

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