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POIf I stop a long running query, does it rollback?
 

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  1. POIf I stop a long running query, does it rollback?
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    <p>A query that is used to loop through <b>17 millions records to remove duplicates</b> has been running now for about <b>16 hours</b> and I wanted to know if the query is stopped right now if it will finalize the delete statements or if it has been deleting while running this query? Indeed, if I do stop it, does it finalize the deletes or rolls back?</p> <p>I have found that when I do a </p> <pre><code> select count(*) from myTable </code></pre> <p>That the rows that it returns (while doing this query) is about 5 less than what the starting row count was. Obviously the server resources are extremely poor, so does that mean that this process has taken 16 hours to find 5 duplicates (when there are actually thousands), and this could be running for days?</p> <p>This query took 6 seconds on 2000 rows of test data, and it works great on that set of data, so I figured it would take 15 hours for the complete set.</p> <p>Any ideas?</p> <p>Below is the query:</p> <pre><code>--Declare the looping variable DECLARE @LoopVar char(10) DECLARE --Set private variables that will be used throughout @long DECIMAL, @lat DECIMAL, @phoneNumber char(10), @businessname varchar(64), @winner char(10) SET @LoopVar = (SELECT MIN(RecordID) FROM MyTable) WHILE @LoopVar is not null BEGIN --initialize the private variables (essentially this is a .ctor) SELECT @long = null, @lat = null, @businessname = null, @phoneNumber = null, @winner = null -- load data from the row declared when setting @LoopVar SELECT @long = longitude, @lat = latitude, @businessname = BusinessName, @phoneNumber = Phone FROM MyTable WHERE RecordID = @LoopVar --find the winning row with that data. The winning row means SELECT top 1 @Winner = RecordID FROM MyTable WHERE @long = longitude AND @lat = latitude AND @businessname = BusinessName AND @phoneNumber = Phone ORDER BY CASE WHEN webAddress is not null THEN 1 ELSE 2 END, CASE WHEN caption1 is not null THEN 1 ELSE 2 END, CASE WHEN caption2 is not null THEN 1 ELSE 2 END, RecordID --delete any losers. DELETE FROM MyTable WHERE @long = longitude AND @lat = latitude AND @businessname = BusinessName AND @phoneNumber = Phone AND @winner != RecordID -- prep the next loop value to go ahead and perform the next duplicate query. SET @LoopVar = (SELECT MIN(RecordID) FROM MyTable WHERE @LoopVar &lt; RecordID) END </code></pre>
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    1. USRyanKeeter
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    1. COThe problem is you are calling SELECT MIN(RecordID) each time through the loop. I suggest you rewrite your SQL. Depending on your indexes, this is could be a table scan each time through the loop. i.e. O(n^2) which is why your time estimate is incorrect. It will take days if not weeks!
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      1. USMitch Wheat
 

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