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Editorial Team
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Asked: 2026-06-14T17:00:42+00:00

Just wondering what happens to the foreign key constrains of a source table, when

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Just wondering what happens to the foreign key constrains of a source table, when it is replicated using CREATE...SELECT statement. Will the referential constraints be copied or ignored?

Here is an example:

CREATE TABLE foo(a int, b int, PRIMARY KEY(a));
CREATE TABLE source(id int, a int, PRIMARY KEY(id), FOREIGN KEY(a) REFERENCES foo(a));

CREATE TABLE target SELECT * FROM source;

So, my question is if attribute a on target also points to foo(a)? If the answer is vendor specific, I’m looking the answer for MySQL.

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1 Answer

  1. Editorial Team

    No, it won’t create the FK constraint in target. CREATE TABLE…SELECT just looks at the columns and data types of the SELECT result set, and that determines the definition of the new table.

    I thought that using CREATE TABLE…LIKE could be a workaround for you, but I tested it on MySQL 5.5, and it also does not create the foreign keys.

    CREATE TABLE target LIKE source;

    I’m guessing because foreign keys are implemented in the InnoDB storage engine, not recognized by the storage-independent layer of MySQL, they probably don’t show up in the storage-independent .FRM file.

    This bug seems to confirm that CREATE TABLE…LIKE is implemented by simply copying the .FRM file: http://bugs.mysql.com/bug.php?id=35526

    But the fix mentioned was put into the MySQL 6.1 branch, and that branch was killed long ago.

    So for now, you’ll have to declare the foreign keys as a separate step. I understand that in the future, the .FRM file is going away, so they’ll have to change how CREATE TABLE…LIKE works. Anyway, that doesn’t help you today.

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