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Can a hash index be used on a lookup?
Furthermore, be aware that indexes on combinations of ID and Lookup alone may not be optimal, as your WHERE predicate also filters on tablea.Elg_IDpart1 and tableb.IDpart1 —you may benefit from indexing on those columns too. Can I have a single hash index, and the rest of the indexes b B-tree index?
How does a hash index fit for as an optimization technique?
All of the indexes are normal B-trees. I currently have indexes on both ID, Lookup sperately, and as one index, and it is a B-Tree index. Based on my WHERE Clause, does a hash index fit for as an optimization technique?? As documented under CREATE INDEX Syntax:
How are hash indexes different from equality comparisons?
Hash indexes have somewhat different characteristics from those just discussed: They are used only for equality comparisons that use the = or <=> operators (but are very fast). They are not used for comparison operators such as < that find a range of values.
How are B-tree and hash indexes used?
Understanding the B-tree and hash data structures can help predict how different queries perform on different storage engines that use these data structures in their indexes, particularly for the MEMORY storage engine that lets you choose B-tree or hash indexes.
How to set MySQL hash indexes for optimization?
UPDATE schema1.tablea a JOIN schema1.tableb b USING (ID, Lookup) SET a.Elg_IDpart1 = b.IDpart1, a.Elg_IDpart2 = b.IDpart2 WHERE a.Elg_IDpart1 IS NULL AND a.ID IS NOT NULL AND b.IDpart1 IS NOT NULL AND b.Lookup IS NOT NULL ORDER BY ID, Lookup
How are indexes selected for use in MySQL?
Are the indexes being selected for use by MySQL (bear in mind that it can only use one index per table for lookups: for testing both the JOIN predicate and the filter predicates: perhaps you need an appropriate composite index)? Check the query execution plan by using EXPLAIN to investigate such issues further.