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MySQL Cookbook
book

MySQL Cookbook

by Paul DuBois
October 2002
Intermediate to advanced content levelIntermediate to advanced
1024 pages
27h 26m
English
O'Reilly Media, Inc.
Content preview from MySQL Cookbook

Managing Multiple SimultaneousAUTO_INCREMENT Values

Problem

You’re working with two or more tables that contain AUTO_INCREMENT columns, and you’re having a hard time keeping track of the sequence values generated for each table.

Solution

Save the values in SQL variables for later. If you’re using queries from within a program, save the sequence values in program variables; or you may be able to issue the queries using separate connection or statement objects to keep them from getting mixed up.

Discussion

As described in Recipe 11.6, the LAST_INSERT_ID( ) server-side sequence value indicator function is set each time a query generates an AUTO_INCREMENT value, whereas client-side sequence indicators may be reset for every query. What if you issue a statement that generates an AUTO_INCREMENT value, but don’t want to refer to that value until after issuing a second statement that also generates an AUTO_INCREMENT value? In this case, the original value no longer will be accessible, either through LAST_INSERT_ID( ) or as a client-side value. To retain access to it, you should save the value first before issuing the second statement. There are several ways to do this:

  • At the SQL level, you can save the value in a SQL variable after issuing a query that generates an AUTO_INCREMENT value:

    INSERT INTO tbl_name (id,...) VALUES(NULL,...);
    SET @saved_id = LAST_INSERT_ID( );

    Then you can issue other statements without regard to their effect on LAST_INSERT_ID( ). To use the original AUTO_INCREMENT ...

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Publisher Resources

ISBN: 0596001452Catalog PageErrata