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https://dev.mysql.com/doc/internals/en/optimizer-not-relations.html
It is a logical rule that column1 <> 5 is the same as column1 < 5 OR column1 > 5 However, MySQL does not transform in this circumstance. If you think that a range search would be better, then you should do your own transforming in such cases. It is ...
https://dev.mysql.com/doc/internals/en/optimizer-nulls-filtering.html
This section discusses the NULLs filtering optimization used for ref and eq_ref joins.
https://dev.mysql.com/doc/internals/en/optimizer-union-queries.html
Therefore, for this query: SELECT * FROM Table1 WHERE column1 = 'x' UNION ALL SELECT * FROM TABLE1 WHERE column2 = 'y' if both column1 and column2 are indexed, then each SELECT is done using an indexed search, and the result sets are merged. Notice ...
https://dev.mysql.com/doc/refman/8.4/en/data-size.html
The compact family of row formats also optimizes CHAR column storage when using a variable-length character set such as utf8mb3 or utf8mb4. Design your tables to minimize their space on the disk. This can result in huge improvements by reducing the ...
https://dev.mysql.com/doc/internals/en/information-schema-optimizer-trace-table.html
TRACE: The trace, in JSON format (see json.org: basically it has scalars (number, string, bool) and structures (either arrays or associative arrays)).
https://dev.mysql.com/doc/internals/en/optimizer-constant-propagation.html
Probably they should not apply for LIKE either, but that's a story for another day. Constant propagation happens in a loop, so the output from one propagation step can be input for the next step.
https://dev.mysql.com/doc/internals/en/optimizer-early-nulls-filtering.html
Suppose we have a join order such as this one: ..., tblX, ..., tblY, ... Suppose further that table tblY is accessed via ref or eq_ref access on tblY.key_column = tblX.column or, in the case of ref access using multiple key parts, via ... Here the ...
https://dev.mysql.com/doc/internals/en/optimizer-partition-selection.html
If a partitioned table is accessed in a series of index lookups (that is, using the ref, eq_ref, or ref_or_null access methods), MySQL checks to see whether it needs to make index lookups in all partitions or that it can limit access to a ...
https://dev.mysql.com/doc/internals/en/optimizer-trace-implementation.html
A trace is started by creating an instance of Opt_trace_start; information is added to this trace by creating instances of Opt_trace_object and Opt_trace_array, and by using the add() functions of those classes...
https://dev.mysql.com/doc/internals/en/optimizer-trace-system-variable.html
The optimizer_trace system variable has these on/off switches: enabled: allows to enable/disable tracing one_line: if on, the trace will have no whitespace; it's unreadable for humans but readable for JSON parsers (they ignore whitespace); the only ...