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No Functions on Left Side of Operator

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Don’t use functions on a column in the where clause

You will get an index scan instead of a seek, take a look these two queries. The first query uses a function while the second does not and is therefore sargable

  1. SELECT * FROM Orders WHERE LEFT(CustomerID,1) ='V'
  2. SELECT * FROM Orders WHERE CustomerID LIKE 'V%'

Here is the execution plan

QueryPlan2 0.jpg

Contributed by: --SQLDenis 15:24, 31 May 2008 (GMT)

Part of SQL Server Programming Hacks - 100+ List

Section Query Optimization

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