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MySQL: limit results to items with at least one child item

Posted on 2011-05-04
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Last Modified: 2012-06-21
With MySQL, I want to limit results to items with at least one child item.

My table has a column named `ParentID` and I only want results where at least one item uses the item returned as its `ParentID`

SELECT `Name`,`ID` FROM `File` WHERE `ClassName` = 'Folder' AND  (there is at least one `File` with the `ParentID` of this `ID`)

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Question by:hankknight
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Assisted Solution

by:hielo
hielo earned 800 total points
ID: 35694990
try:
SELECT `Name`,`ID` FROM `File` WHERE `ClassName` = 'Folder' 
AND  `File`.`ID` IN (SELECT `f2`.`ID` FROM `File` as `f2` WHERE `f2`.`ID`=`File`.`ID`)

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by:
Walter Ritzel earned 1200 total points
ID: 35694993
SELECT `Name`,`ID` FROM `File` F1 WHERE `ClassName` = 'Folder' AND  exists (select 1 from `File` where `parentid` = F1.`ID` group by `parentid` having count(1) >=1)
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by:hankknight
ID: 35695019
Thank you both.  hielo, I modified your code to make it work.  

wpcortes, your code works as is.

SELECT `Name`,`ID` FROM `File` WHERE `File`.`ClassName` = 'Folder' 
AND `File`.`ID` IN (SELECT `f2`.`ParentID` FROM `File` as `f2` WHERE `f2`.`ParentID`=`File`.`ID`)

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