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PORemoving duplicates from result of multiple join on tables with different columns in MySQL
 

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  1. PORemoving duplicates from result of multiple join on tables with different columns in MySQL
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    <p>I am trying to make one statement to pull data from 3 related tables (as in they all share a common string index). I am having trouble preventing MySQL from returning the product of two of the tables, making the result set much larger than I want it. Each table has a different number of columns, and I would prefer to not use UNION anyway, because the data in each table is separate. </p> <p>Here is an example:</p> <p>Table X is the main table and has fields A B.</p> <p>Table Y has fields A C D.</p> <p>Table Z has fields A E F G.</p> <p>-</p> <p>My ideal result would have the form:</p> <pre><code>A1 B1 C1 D1 E1 F1 G1 A1 B2 C2 D2 00 00 00 A2 B3 C3 D3 E2 F2 G2 A2 B4 00 00 E3 F3 G3 </code></pre> <p>etc...</p> <p>-</p> <p>Here is the simplest SQL I have tried that shows my problem (that is, it returns the product of Y * Z indexed by data from A:</p> <pre><code>SELECT DISTINCT * FROM X LEFT JOIN Y USING (A) LEFT JOIN Z USING (A) </code></pre> <p>-</p> <p>I have tried adding a group by clause to fields on Y and Z. But, if I only group by one column, it only returns the first result matched with each unique value in that column (ie: A1 C1 E1, A1 C2 E1, A1 C3 E1). And if I group by two columns it returns the product of the two tables again.</p> <p>I've also tried doing multiple select statements in the query, then joining the resulting tables, but I received the product of the tables as output again.</p> <p>Basically I want to merge the results of three select statements into a single result, without it giving me all combinations of the data. If I need to, I can resort to doing multiple queries. However, since they all contain a common index, I feel there should be a way to do it in one query that I am missing.</p> <p>Thanks for any help.</p>
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    1. COOk, maybe this will make it easier to understand my problem. Just ignore table X and try to join table Y and Z on field A. IE: SELECT * FROM Y INNER JOIN Z USING (A). You will see that this outputs the product of the two tables.
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