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POInnoDB: Copying a number of records along with their tag memberships
 

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  1. POInnoDB: Copying a number of records along with their tag memberships
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    <p><strong>Foreign keys might be appropriate to this problem/solution. However, I have inherited this code and db, which do not use foreign keys, and so it would be difficult to add them. If absolutely necessary I can do it, but I'd prefer not to.</strong></p> <p>Let's pretend that I have a very simple set of tables in an <code>InnoDB</code> database that are used to store a bunch of jokes, each of which belongs to particular group and may have one or more tags associated with it. I am using <code>PHP/MySQLi</code> to do the work. Let's say the tables look like so:</p> <pre><code>GROUPS id (int, primary, auto_inc) | group_name (varchar[64]) ============================================================ 1 knock, knock jokes 2 one-liners JOKES id (int, primary, auto_inc) | group_id (int) | joke_text (varchar[255]) ============================================================================= 1 1 interrupting cow. inte-MOO! TAGS id (int, primary, auto_inc) | tag_text (varchar[255]) ============================================================================= 1 explicit 2 hilarious JOKE_TAGS id (int, primary, auto_inc) | joke_id (int) | tag_id (int) ============================================================================= 1 1 1 </code></pre> <p><em>Even though it makes no sense in the context of these jokes</em>, let's just say that the user has the option to copy the jokes from one group to another. Thanks to users' help on this site, I have figured out that the easiest way to do that would be something like the following:</p> <pre><code>INSERT INTO jokes (group_id,joke_text) SELECT '$dstGroupID', r2.joke_text FROM jokes AS j2 WHERE j2.group_id = '$srcGroupID'; </code></pre> <p>That seems to work just fine. However, I am completely lost as to how I can efficiently copy over the tag memberships. For instance, if I was to copy the <code>jokes</code> from <code>group.id=1</code> to <code>group.id=2</code> (using the sample data shown above), I would want the <code>JOKE_TAGS</code> table to look like so:</p> <pre><code>JOKE_TAGS id (int, primary, auto_inc) | joke_id (int) | tag_id (int) ============================================================================= 1 1 1 2 2 1 </code></pre> <p>For the life of me, I simply cannot figure out a way to do this without throwing away the SQL above and simply iterating through every single <code>joke</code> that is being copied, with the logic looking something like this:</p> <ul> <li>Pull out a joke's information</li> <li>Pull out that joke's tag memberships</li> <li>Insert a new record into <code>JOKES</code> with the pulled out info from above</li> <li>Grab the id of the newly inserted joke</li> <li>Insert a new record into <code>JOKE_TAGS</code>, using the id grabbed above</li> </ul> <p>This is obviously WILDLY inefficient when compared to the 'copying' SQL listed above. If anyone can suggest a more efficient solution, I'd be most appreciative.</p>
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