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| − | I use a database often, mostly for structuring and holding the data at EnergyTeachers.org. I usually use MySQL, but also sometimes sqlite. Here are some of my tricks.
| + | Stands back from the kyeboard in amazement! Thanks! |
| − | ===Finding Duplicates===
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| − | It's one thing to identify data that is duplicate, and you see hints how to do it by counting members in a group grouped by what field(s) should be duplicate and showing those groupings that have a count larger than one. But we often want to do something to the duplicate, like delete it. A better method in SQL is to create two tables from one and find pairings across them. Here's the code for showing all duplicate rows where two fields match exactly:
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| − | SELECT t1.*
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| − | FROM tablename as t1, tablename as t2
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| − | WHERE t1.uniqueid<>t2.uniqueid AND t1.field1=t2.field1 AND t1.field2=t2.field2
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| − | ORDER BY t1.field1, t1.field2
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| − | The first WHERE condition ensures we don't match rows to themselves. This only works on tables where there is a unique id.
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| − | We use ORDER BY to show the duplicates in adjacent rows in the result.
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| − | [[Category:Computers]]
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Revision as of 20:12, 2 January 2012
Stands back from the kyeboard in amazement! Thanks!
