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POhow do I speed up substr searches in my query
 

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  1. POhow do I speed up substr searches in my query
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    <p>I am using this as a sub select (in a simple query joining 2 other tables) and as you can imagine it takes a while to run. going on 6 hours+ so far. is this the only way to do this? I know that doing another JOIN instead of a sub select might help a bit. but the main bottleneck is all these OR's and sub-strings. </p> <pre><code>SELECT ex_array FROM service_x WHERE ( substr(ex_array,1,2) = 'FW' OR substr(ex_array,3,2) = 'FW' OR substr(ex_array,5,2) = 'FW' OR substr(ex_array,7,2) = 'FW' OR substr(ex_array,9,2) = 'FW' OR substr(ex_array,11,2) = 'FW' ) OR ( substr(ex_array,1,2) = 'IL' OR substr(ex_array,3,2) = 'IL' OR substr(ex_array,5,2) = 'IL' OR substr(ex_array,7,2) = 'IL' OR substr(ex_array,9,2) = 'IL' OR substr(ex_array,11,2) = 'IL' ) OR ( substr(ex_array,1,2) = 'IN' OR substr(ex_array,3,2) = 'IN' OR substr(ex_array,5,2) = 'IN' OR substr(ex_array,7,2) = 'IN' OR substr(ex_array,9,2) = 'IN' OR substr(ex_array,11,2) = 'IN' ) OR ( substr(ex_array,1,2) = 'IK' OR substr(ex_array,3,2) = 'IK' OR substr(ex_array,5,2) = 'IK' OR substr(ex_array,7,2) = 'IK' OR substr(ex_array,9,2) = 'IK' OR substr(ex_array,11,2) = 'IK' ) OR ( substr(ex_array,1,2) = 'IH' OR substr(ex_array,3,2) = 'IH' OR substr(ex_array,5,2) = 'IH' OR substr(ex_array,7,2) = 'IH' OR substr(ex_array,9,2) = 'IH' OR substr(ex_array,11,2) = 'IH' ) OR ( substr(ex_array,1,2) = 'KP' OR substr(ex_array,3,2) = 'KP' OR substr(ex_array,5,2) = 'KP' OR substr(ex_array,7,2) = 'KP' OR substr(ex_array,9,2) = 'KP' OR substr(ex_array,11,2) = 'KP' ) ) </code></pre>
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    1. USa_horse_with_no_name
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      1. POhow do I speed up substr searches in my query
      1. USJon Heller
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    1. CODo you have an explain plan for the query (check out dbms_xplan to obtain this)? I expect the query is being satisfied by a full table scan since you have stopped the database using any standard indexes by applying the function to ex_array. The six function based indexes suggested by @dcp would possibly help. How many rows does service_x have, and what percentage of rows do you expect to be returned by your query? You may need to reevaluate your overall algorithm/design to get the performance you require. The key though will likely be to enable an index access, depending on query selectivity.
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      1. USmathewbutler
    2. COabout 12.2 million rows (in service_x) and I should be getting about 175,000 results back.
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    3. COGiven the high selectivity of the query - I suggest that if you are unable to tune the whole algorithm your best option is to modify the query to enable an efficient filter of rows via an index access to ex_array. I'll post an answer below that may help.
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