# Sql Tuning Principles (C)

+ Avoiding situations where indexes cannot be used
  + Avoid implicit conversions (type mismatch)
  + Avoid using function on indexed columns in WHERE predicates
  + Avoid using fuzzy query for search column prefixes:`%abc`
  + Avoid reverse match operator in WHERE predicates:`!=, <>`
  + Too much data after index filtering may cause the optimizer to choose to perform a full table scan
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