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PODeleting old records while keeping a minimum number of records per parent
 

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  1. PODeleting old records while keeping a minimum number of records per parent
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    <p>My question is similar to <a href="https://stackoverflow.com/q/210515/66169">sql statement to delete records older than XXX as long as there are more than YY rows</a>, but that question just deals with a single parent, I want to delete records for all parents in one go.</p> <p>Consider this table:</p> <pre><code>CREATE TABLE Children ( ChildId int NOT NULL, ChildCreated datetime NOT NULL, ParentId int NOT NULL ) </code></pre> <p>This could be any parent-child relationship, so the names are generic. </p> <p>I would like to delete all children that are older than a month, but need to keep a minimum number of children for each parent regardless of their age.</p> <p>I tried some statements with nested SELECTs and GROUP BYs which gave me some results but none gave me the correct result set. </p> <p>Because I am using SQL Server I came up with the following solution that works great:</p> <pre><code>WITH CTE AS ( SELECT ROW_NUMBER() OVER (Partition BY ParentId ORDER BY ChildCreated DESC) As RowNo, ChildCreated FROM Children ) DELETE FROM CTE WHERE RowNo &gt; 10 AND RevisionCreated &lt; DATEADD(MONTH,-1,GetDate()) </code></pre> <p>The common table expression groups all children for each parent together and adds a continuous row number based on the creation order. The newest child for each parent has a row number of 1, the tenth newest has 10. So I can just delete all records with a row number greater 10 as long as they are also over a month old.</p> <p>My question is, what if I have to do the same thing on a system where CTEs are not supported. What is the <strong>ANSI SQL-92</strong> solution for this problem?</p>
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    1. USCommunity
    1. USPeter Hahndorf
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    1. COAs far as I am aware CTEs *are* valid in the ANSI SQL 99 standard. Perhaps you want a solution for a database that does *not* support the standard? (MySQL perhaps?)
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      1. USMark Byers
    2. CO@MarkByers I wasn't aware of CTEs being in SQL-99, yes I would be interested in a solution for systems where CTEs are not supported. I changed the question to ask for SQL-92.
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      1. USPeter Hahndorf
 

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