Question

So I have a table like this:

create table `test` ( 
`testId` int(11) not null auto_increment, 
`text` varchar(10) not null default '',
primary key(`testId`),
unique(`text`)
) engine=innodb;

My insert would be

1. insert into test (text) values (‘a’);
2. insert into test (text) values (‘b’);
3. insert into test (text) values (‘a’);

the 3rd insert will fail, but I want it to return the testId for the duplicate (for ‘a’).

Is this possible without writing a second query?

Answer 1

You can’t do this in an INSERT query because the INSERT does not return any rows.

When an INSERT fails because of a duplicated key – normally the thing that built the query knows what data it sent, so it could use this.

You may be able to achieve what you want by using 12.2.5.3. INSERT … ON DUPLICATE KEY UPDATE

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;