138

I am trying to delete from a few tables at once. I've done a bit of research, and came up with this

DELETE FROM `pets` p,
            `pets_activities` pa
      WHERE p.`order` > :order
        AND p.`pet_id` = :pet_id
        AND pa.`id` = p.`pet_id`

However, I am getting this error

Uncaught Database_Exception [ 1064 ]: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'p, pets_activities pa...

I've never done a cross table delete before, so I'm inexperienced and stuck for now!

What am I doing wrong?

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7 Answers 7

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251

Use a JOIN in the DELETE statement.

DELETE p, pa
      FROM pets p
      JOIN pets_activities pa ON pa.id = p.pet_id
     WHERE p.order > :order
       AND p.pet_id = :pet_id

Alternatively you can use...

DELETE pa
      FROM pets_activities pa
      JOIN pets p ON pa.id = p.pet_id
 WHERE p.order > :order
   AND p.pet_id = :pet_id

...to delete only from pets_activities

See this.

For single table deletes, yet with referential integrity, there are other ways of doing with EXISTS, NOT EXISTS, IN, NOT IN and etc. But the one above where you specify from which tables to delete with an alias before the FROM clause can get you out of a few pretty tight spots more easily. I tend to reach out to an EXISTS in 99% of the cases and then there is the 1% where this MySQL syntax takes the day.

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7 Comments

I tried this "delete all in 1 query" with joining 6 large tables (everyone about ~15k rows) and the query took 155 seconds to delete 63 rows in 6 tables :O
@cadman This is the real right answer; there may be arguments against using it, but it's very useful on occasion
+1 I agree that this in the real right answer, since the question was not "should you" but "how to". However, I would be interested in hearing about the 1% because I can't think of a single situation where this would be preferred.
@techouse, did you join and filter on indices? 15k x 15k x 15k x 15k 15k x 15k is 11 million. Did a SELECT take similarly long?
You can also use LEFT JOIN, which is usefull if the second table had no matching entries, else nothing will be deleted.
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21

Since this appears to be a simple parent/child relationship between pets and pets_activities, you would be better off creating your foreign key constraint with a deleting cascade.

That way, when a pets row is deleted, the pets_activities rows associated with it are automatically deleted as well.

Then your query becomes a simple:

delete from `pets`
    where `order` > :order
      and `pet_id` = :pet_id
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16 Comments

@Erick, provided you've set up referential integrity, cascading deletes can cause no more trouble than delete on its own. We already know that pa is a proper child of p due to the id/pet_id mapping.
Well, you guys have your own thoughts but it seems like you're discounting a lot of the power of DBMS'. Cascading deletes are as much a part of data management as triggers, stored procedures or constraints and they're only dangerous if you don't know what you're doing. Still, I won't argue the point further, we'll just have to agree to disagree.
Erick, now you've piqued my interest. How do you ensure data integrity within the database without constraints?
@Erick said, "I also do not use triggers, stored procedures, or constraints." Ah, you use Excel. :-)
I just want to follow up on this. I have changed my position on deleting cascades in this situation. I have been a part of a new SQL environment which used them, and used them well and they were very organized. In this system it worked very well to our advantage to have these cascades in place. It certainly prevented orphaned data and was not dangerous. The problem is that everyone working with the database needs to understand how to use them safely. But there are always risks when junior devs are making database changes unsupervised.
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21

Use this

DELETE FROM `articles`, `comments` 
USING `articles`,`comments` 
WHERE `comments`.`article_id` = `articles`.`id` AND `articles`.`id` = 4

or 

DELETE `articles`, `comments` 
FROM `articles`, `comments` 
WHERE `comments`.`article_id` = `articles`.`id` AND `articles`.`id` = 4
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1 Comment

Found a good reference for using this and a few other options at mysqltutorial.org/mysql-delete-statement.aspx
3

To anyone reading this in 2017, this is how I've done something similar.

DELETE pets, pets_activities FROM pets inner join pets_activities
on pets_activities.id = pets.id WHERE pets.`order` > :order AND 
pets.`pet_id` = :pet_id

Generally, to delete rows from multiple tables, the syntax I follow is given below. The solution is based on an assumption that there is some relation between the two tables.

DELETE table1, table2 FROM table1 inner join table2 on table2.id = table1.id
WHERE [conditions]
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2

I don't have a mysql database to test on at the moment, but have you tried specifying what to delete prior to the from clause? For example:

DELETE p, pa FROM `pets` p,
        `pets_activities` pa
  WHERE p.`order` > :order
    AND p.`pet_id` = :pet_id
    AND pa.`id` = p.`pet_id`

I think the syntax you used is limited to newer versions of mysql.

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1 Comment

That query executed successfully, however, it didn't delete any rows (but I believe it should have).
1

I found this article which showing you how to delete data from multiple tables by using MySQL DELETE JOIN statement with good explanation.

enter image description here

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Comments

1

The syntax looks right to me ... try to change it to use INNER JOIN ...

Have a look at this.

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1 Comment

Too bad you didn't include the actual solution, because the link is correct!

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