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    Archive for October 18th, 2007

    MySQL: INSERT IF NOT EXISTS syntax

    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:

    1. CREATE TABLE `transcripts` (
    2.  `ensembl_transcript_id` varchar(20) NOT NULL,
    3.  `transcript_chrom_start` int(10) unsigned NOT NULL,
    4.  `transcript_chrom_end` int(10) unsigned NOT NULL,
    5.  PRIMARY KEY  (`ensembl_transcript_id`)
    6. ) 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: 1) repeated executions of the pipeline will not destroy our database, and 2) repeated executions will not die due to ‘duplicate primary key’ errors.

    Method 1: using REPLACE
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