Sargable DATE and YEAR

Starting from MariaDB 11.1, conditions in the form

YEAR(indexed_date_col) CMP const_value
DATE(indexed_date_col) CMP const_value

are sargable, provided that

• CMP is any of =, <=>, <, <=, >, >= .

• indexed_date_col has a type of DATE, DATETIME or TIMESTAMP and is a part of some index.

One can swap the left and right hand sides of the equality: const_value CMP {DATE|YEAR}(indexed_date_col) is also handled.

Sargable here means that the optimizer is able to use such conditions to construct access methods, estimate their selectivity, or use them to perform partition pruning.

Implementation

Internally, the optimizer rewrites the condition to an equivalent condition which doesn't use YEAR or DATE functions.

For example, YEAR(date_col)=2023 is rewritten intodate_col between '2023-01-01' and '2023-12-31'.

Similarly, DATE(datetime_col) <= '2023-06-01' is rewritten intodatetime_col <= '2023-06-01 23:59:59'.

Controlling the Optimization

The optimization is always ON, there is no Optimizer Switch flag to control it.

Optimizer Trace

The rewrite is logged as date_conds_into_sargable transformation. Example:

{
            "transformation": "date_conds_into_sargable",
            "before": "cast(t1.datetime_col as date) <= '2023-06-01'",
            "after": "t1.datetime_col <= '2023-06-01 23:59:59'"
          },

References

• MDEV-8320: Allow index usage for DATE(datetime_column) = const

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