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POIndex Columns and Order
 

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    <p>If I have a select statement like the statement below, what order and what columns should be included in an index?</p> <pre><code>SELECT MIN(BenchmarkID), MIN(BenchmarkDateTime), Currency1, Currency2, BenchmarkType FROM Benchmark INNER JOIN MyCurrencyPairs ON Currency1 = Pair1 AND Currency2 = Pair2 WHERE BenchmarkDateTime &gt; IN_BeginningTime GROUP BY Currency1, Currency2, BenchmarkType; </code></pre> <p>Items to note:</p> <ul> <li>The Benchmark table will have billions of rows</li> <li>The MyCurrencyPairs table is a local table that will have less than 10 records</li> <li>IN_BeginningTime is a input parameter</li> <li>Columns Currency1 and Currency2 are VARCHARs</li> <li>Columns BenchmarkID and BenchmarkType are INTs</li> <li>Column BenchmarkDateTime is a datetime (hopefully that was obvious)</li> </ul> <p>I've created an index with Currency1, Currency2, BenchmarkType, BenchmarkDateTime, and BenchmarkID but I wasn't getting the speed I was wanting. Could I create a better index?</p> <hr> <p>Edit #1: Someone requested the explain results below. Let me know if anything else is needed</p> <p><img src="https://i.stack.imgur.com/QvAHM.png" alt="enter image description here"></p> <hr> <p>Edit #2: Someone requested the DDL (I'm assuming this is the create statement) for the two tables:</p> <p>(this benchmark table exists in the database)</p> <pre><code>CREATE TABLE `benchmark` ( `SequenceNumber` INT(11) NOT NULL, `BenchmarkType` TINYINT(3) UNSIGNED NOT NULL, `BenchmarkDateTime` DATETIME NOT NULL, `Identifier` CHAR(6) NOT NULL, `Currency1` CHAR(3) NULL DEFAULT NULL, `Currency2` CHAR(3) NULL DEFAULT NULL, `AvgBMBid` DECIMAL(18,9) NOT NULL, `AvgBMOffer` DECIMAL(18,9) NOT NULL, `AvgBMMid` DECIMAL(18,9) NOT NULL, `MedianBMBid` DECIMAL(18,9) NOT NULL, `MedianBMOffer` DECIMAL(18,9) NOT NULL, `OpenBMBid` DECIMAL(18,9) NOT NULL, `ClosingBMBid` DECIMAL(18,9) NOT NULL, `ClosingBMOffer` DECIMAL(18,9) NOT NULL, `ClosingBMMid` DECIMAL(18,9) NOT NULL, `LowBMBid` DECIMAL(18,9) NOT NULL, `HighBMOffer` DECIMAL(18,9) NOT NULL, `BMRange` DECIMAL(18,9) NOT NULL, `BenchmarkId` INT(11) NOT NULL AUTO_INCREMENT, PRIMARY KEY (`BenchmarkId`), INDEX `NextBenchmarkIndex01` (`Currency1`, `Currency2`, `BenchmarkType`), INDEX `NextBenchmarkIndex02` (`BenchmarkDateTime`, `Currency1`, `Currency2`, `BenchmarkType`, `BenchmarkId`), INDEX `BenchmarkOptimization` (`BenchmarkType`, `BenchmarkDateTime`, `Currency1`, `Currency2`) ) </code></pre> <p>(I'm creating the MyCurrencyPairs table in my routine)</p> <pre><code>CREATE TEMPORARY TABLE MyCurrencyPairs ( Pair1 VARCHAR(50), Pair2 VARCHAR(50) ) ENGINE=memory; CREATE INDEX IDX_MyCurrencyPairs ON MyCurrencyPairs (Pair1, Pair2); </code></pre>
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    1. COCan you run an EXPLAIN <SELECT STATEMENT HERE> and post the results.
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    2. COThanks for the explain. The Currency1 and 2 fields, are they varchar for a reason? i.e. contain text? If so, is there any way you could convert those to lookups instead so the field types could be changed to INT? i.e. "GBP" => 1, "USD" => 2
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    3. COSadly no... this is a system that's been here a while and that would be a major change. I wish the original architect had done that... no idea why you would try to match everything on VARCHARs.....
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