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Indexes - Coggle Diagram

- - - - data access is fast
      - queries that use covering indexes can use the primary key values contained at the leaf node
      - keep related data close together
    - - clustered tables can be slower for full table scans
      - secondary (nonclustered) indexes can be larger than you might expect
      - updating the clustered index columns is expensive
      - secondary index accesses require two index lookups instead of one
      - insert speeds depend heavily on insertion order
- - - - match the full value
      - index-only queries
      - match one part exactly and match a range on another part
      - match a range of values
      - match a column prefix
      - match a leftmost prefix
    - - can’t skip columns in the index
      - can’t optimize accesses
      - not useful if the lookup does not start from the leftmost side of the indexed columns
  - - - don’t support partial key matching
      - support only equality comparisons that use the =, IN(), and <=> operators
      - can’t use hash indexes for sorting
      - slow if there are many hash collisions
      - can’t use the values in the index to avoid reading the rows