How can I do ‘insert if not exists’ in MySQL?


There’s also INSERT … ON DUPLICATE KEY UPDATE syntax, and you can find explanations in INSERT … ON DUPLICATE KEY UPDATE Statement.

Post from according to Google’s webcache:

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

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`)

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

  1. repeated executions of the pipeline will not destroy our
    > database
  1. 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.


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.

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