indexing - Mysql - Which index is better? -

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i have 2 column this:

column | column b

and these column searchable. want search both of them @ same time. should index pair of key (a,b) or index seperate , b. 1 better?

a composite index on (a, b) may used queries involving only a , queries involving both a , b, never on queries involving b.

which index better depends on queries performing on data.

not that, order of fields in index relevant, since index on (a, b) , index on (b, a) may useful in different situations.

to complicate matters more, queries can use index alone without accessing data in tables, e.g., if query select b table = 5 , have index on (a, b), engine may traverse index, since contains data need.


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