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MYSQL Performance Tips

Building a composite index

In many situations, a composite index performs better than an index with a single column. To build an optimal composite index, populate it with columns in this order.

.= column(s) from the WHERE clause first. (eg, INDEX(a,b,...) for WHERE a=12 AND b='xyz' ...)

.IN column(s); the optimizer may be able to leapfrog through the index.

.One "range" (eg x BETWEEN 3 AND 9, name LIKE 'J%') It won't use anything past the first range column.

.All the columns in GROUP BY, in order

.All the columns in ORDER BY, in order. Works only if all are ASC or all are DESC or you are using 8.0.

Notes and exceptions:

.Don't duplicate any columns.

.Skip over any cases that don't apply.

.If you don't use all the columns of WHERE, there is no need to go on to GROUP BY, etc.

.There are cases where it is useful to index only the ORDER BY column(s), ignoring WHERE.

.Don't "hide" a column in a function (eg DATE(x) = ... cannot use x in the index.)

.'Prefix' indexing (eg, text_col(99)) is unlikely to be helpful; may hurt.


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