Question

Is it a good idea to index varchar columns only used in LIKE opertations? From what I can read from query analytics I get from the following query:

SELECT * FROM ClientUsers WHERE Email LIKE '%niels@bosmainter%'

I get an “Estimated subtree cost” of 0.38 without any index and 0.14 with an index. Is this a good metric to use for anlayzing if a query has been optimized with an index?

Answer 1

Given the data ‘abcdefg’

WHERE Column1 LIKE '%cde%'  --can't use an index

WHERE Column1 LIKE 'abc%' --can use an index

WHERE Column1 Like '%defg' --can't use an index, but see note below

Note: If you have important queries that require ‘%defg’, you could use a persistent computed column where you REVERSE() the column and then index it. Your can then query on:

WHERE Column1Reverse Like REVERSE('defg')+'%' --can use the persistent computed column's index