MySQL Internals Manual  /  ...  /  The range Join Type The range Join Type

Some conditions can work with indexes, but over a (possibly wide) range of keys. These are known as range conditions, and are most often encountered with expressions involving these operators: >, >=, <, <=, IN, LIKE, BETWEEN

To the optimizer, this expression:

column1 IN (1,2,3) 

is the same as this one:

column1 = 1 OR column1 = 2 OR column1 = 3 

and MySQL treats them the same — there is no need to change IN to OR for a query, or vice versa.

The optimizer will use an index (range search) for

column1 LIKE 'x%'

but not for

column1 LIKE '%x'

That is, there is no range search if the first character in the pattern is a wildcard.

To the optimizer,

column1 BETWEEN 5 AND 7 

is the same as this expression

column1 >= 5 AND column1 <= 7 

and again, MySQL treats both expressions the same.

The optimizer may change a Range to an ALL join type if a condition would examine too many index keys. Such a change is particularly likely for < and > conditions and multiple-level secondary indexes. See: (for MyISAM indexes) /myisam/mi_range.c, mi_records_in_range().

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