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POsql join tomfoolery (or How can I wind up with more rows than when I started?)
 

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  1. POsql join tomfoolery (or How can I wind up with more rows than when I started?)
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    <p>M$ Access 2010</p> <p>table [CONTACT PERSON] has key field [Contact ID] and has 1599 rows. table [Person Client Address Mailing] has key field [ClientID] and has 1465 rows.</p> <p>Not all [CONTACT PERSON].[Contact ID] values have a matching [Person Client Address Mailing].[ClientID]</p> <p>So I'm buffaloed as to how this</p> <pre><code>SELECT aa.[Contact ID], bb.[cstreet1], bb.[cstreet2], bb.[cstreet3], bb.[ccity], bb.[cstate], bb.[czip], bb.[ccountry] FROM [CONTACT PERSON] AS aa LEFT JOIN [Person Client Address Mailing] AS bb ON aa.[Contact ID] = bb.[ClientID] ORDER BY aa.[Contact ID]; </code></pre> <p>can return 1606 rows. My understanding is LEFT JOIN returns every row of the main table and all matching rows of the joined table . Therefore the number of rows returned will always be equal to the number of rows in the main table, never more. What gives? Or is this more Access-specific sql trickery?</p> <p>[new data]</p> <p>Turns out the above query is exactly right - the problem lies with duplicate rows in the joined table, which gets built with this query:</p> <pre><code>SELECT aa.[ClientID], aa.[cstreet1], aa.[cstreet2], aa.[cstreet3], aa.[ccity], aa.[cstate], aa.[czip], aa.[ccountry] FROM AAAddress_X AS aa INNER JOIN ( SELECT gg.[CLIENTID], MIN(gg.[sortOrderPersonPrimary]) AS sortOrderPersonPrimary FROM AAAddress_X AS gg WHERE gg.sortOrderPersonPrimary Is Not Null GROUP BY gg.[CLIENTID]) AS bb ON aa.[CLIENTID] = bb.[CLIENTID] AND aa.[sortOrderPersonPrimary] = bb.[sortOrderPersonPrimary] WHERE aa.[cstreet1] &lt;&gt; "" ORDER BY aa.[CLIENTID]; </code></pre> <p>Running the inner query by itself yields 1458 rows, each ClientID-sortOrderPersonPrimary pairing is unique. And the sortOrderPersonPrimary value is in fact the minimum value, excellent. 1458 + 7 = 1465 so the duplicate rows must be coming in through the joining with the outer query. Which makes sense since there's 7 rows in AAAddress_X with matching ClientID-sortOrderPersonPrimary pairs.</p> <p>So, follow-on question is, how can I adjust the above query to just return only the first occurance of each ClientID with the lowest sortOrderPersonPrimary value? Or maybe a different query, I'm not fussy.</p> <p>Maybe I'm overcomplicating this, so I'll lay out what I have and what I need:</p> <p>Example: AAAddress contains some rows like this: ClientID sortOrderPersonPrimary cstreet1 cstreet2..... 10107 3 123 pine 10108 1 434 olson 10108 1 5454 main 10108 2 434 olivia 10109 2 323 poplar</p> <p>I need: 10107 3 123 pine 10108 1 434 olson 10109 2 323 poplar</p> <p>If there's no way to rid myself of these pesky duplicates in queries my Plan B is to manually pre-create an empty table [Person Client Address Mailing] with fields ClientID and sortOrderPersonPrimary both defined as keys, do an INSERT INTO SELECT... and let the keys implicitly weed out the dupes.</p> <p>Thanks for everone's help so far! You guys rock!</p> <p>Still-learning Steve</p>
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