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MySQL Insert

Posted on 2011-03-04
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Last Modified: 2012-05-11
I am have a brain fart trying to figure out the logic to perform a particular query. Looking for assistance!

The following table is used to store all the items that a child has in his chest. As you can see, a child can have multiple items.

child_id     item_id     quantity
1               1              1
2               1              1
2               1              1
2               4              1
2               4              1
3               8              1
3               9              1
4               2              1

What I am trying to do is give every child item #8 that don't already have it. My first attempt at this query is show in the code section below. However, this doesn't work very well, as it will still return records if the child has other options.
INSERT child_items (child_id, item_id, quantity)
SELECT DISTINCT child_id, 8, 1 
FROM child_items WHERE item_id != 8;

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Question by:plecostomus
2 Comments
 
LVL 142

Accepted Solution

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Guy Hengel [angelIII / a3] earned 500 total points
ID: 35038412
what about:
INSERT child_items (child_id, item_id, quantity)
SELECT child_id, 8, 1 
FROM child_items 
GROUP BY child_id
HAVING MAX(CASE WHEN item_id = 8 THEN 1 ELSE 0 END) = 0

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or:
INSERT child_items (child_id, item_id, quantity)
SELECT child_id, 8, 1 
FROM child_items i
WHERE NOT EXISTS( SELECT NULL FROM child_items o WHERE o.child_id = i.child_id AND o.item_id = 8 )
GROUP BY child_id

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however, not sure if it will actually work in MySQL, you might run into the issue that you cannot select from the same table you do the insert into,
so you might need to run the insert into a temp table first ...

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Author Closing Comment

by:plecostomus
ID: 35038632
Worked perfectly... MySQL 5.0/5.1 allows you to insert into itself from itself.
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