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Asked: 2026-05-11T14:01:14+00:00

I’ve been using SQL for years now but rarely anything more that simple inserts

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I’ve been using SQL for years now but rarely anything more that simple inserts and selects etc… so I’m no SQL expert. I’m wondering if I could get some help in optimizing a more complex SQL statement that I’m executing on SQLite, from PHP through PDO.

The statement seems to work correctly, just seems to take longer that I would have expected (or perhaps I’m just expecting too much).

This is the SQL:

INSERT OR IGNORE INTO MailQueue(SubscriberID, TemplateID)     SELECT Subscribers.ID, '1' AS TemplateID     FROM Subscribers      INNER JOIN SubscriberGroups ON Subscribers.ID=SubscriberGroups.SubscriberID     WHERE SubscriberGroups.GroupID IN ('1', '2', '3')     AND Subscribers.ID NOT IN          (          SELECT Subscribers.ID FROM Subscribers          INNER JOIN SubscriberGroups ON Subscribers.ID=SubscriberGroups.SubscriberID         WHERE SubscriberGroups.GroupID IN ('4', '5', '6')         );

What I’ve got is a list of subscribers, in one or more groups. I want to add subscribers to a mail queue, selecting those that belong to one or more groups (1,2,3) but exclude those that are also in another set of groups (4,5,6).

Firstly, is the above SQL typical of how to do this?

Secondly, what indicies should I have to make this work as efficiently as possible?

Currently it takes about 30 seconds to get through about 5000 subscriber records (and a handful of groups) on a avg spec LAMP.

At the end of the day performance isn’t that critical, but I’d like to understand this stuff better so any insight greatly appreciated.

Brad

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1 Answer

  1. Chances are the extra joins are killing you. What if you do:

    SELECT Subscribers.ID, '1' AS TemplateID FROM Subscribers  WHERE EXISTS( SELECT *                 FROM SubscriberGroups                WHERE Subscribers.ID=SubscriberGroups.SubscriberID                                  AND SubscriberGroups.GroupID IN ('1', '2', '3') )    AND NOT EXISTS( SELECT *                     FROM SubscriberGroups                    WHERE Subscribers.ID=SubscriberGroups.SubscriberID                       AND SubscriberGroups.GroupID IN ('4', '5', '6')     );

    You’d also want to make sure that you have an index on SubscriberGroups( SubscriberID, GroupID )

    My guess is that Subscribers already has an index on ID, right?

    EDIT: Another option, which may or may not be faster. Look at the query plans of each to see…

    This one may be a single index scan which could be faster than two index seeks, but it depends on SQLite’s optimizer…

    SELECT Subscribers.ID, '1' AS TemplateID FROM Subscribers  INNER JOIN( SELECT SUM( CASE WHEN GroupID IN('1', '2', '3') THEN 1 ELSE 0 END ) AS inGroup,                    SUM( CASE WHEN GroupID IN('4', '5', '6') THEN 1 ELSE 0 END ) AS outGroup,                    SubscriberID                             FROM SubscriberGroups                          WHERE SubscriberGroups.GroupID IN ('1', '2', '3', '4', '5', '6' )           ) SubscriberGroups        ON Subscribers.ID=SubscriberGroups.SubscriberID       AND inGroup  > 0       AND outGroup = 0
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