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https://dev.mysql.com/doc/internals/en/optimizer-features-to-trace.html
They are: Greedy search: with a N-table join, this could explore factorial(N) plans Range optimizer Dynamic range optimization (known as "range checked for each record" in EXPLAIN output: each outer row causes a re-run of the range optimizer) ...
https://dev.mysql.com/doc/internals/en/optimizer-index-join-type.html
Consider this query: SELECT column1 FROM Table1; If column1 is indexed, then the optimizer may choose to retrieve the values from the index rather than from the table. For this query: SELECT column1, column2 FROM Table1; the optimizer will use join ...An index which is used this way is called a covering index in most ...
https://dev.mysql.com/doc/internals/en/optimizer-late-nulls-filtering.html
Suppose we have a query plan with table tblX being accessed via the ref access method: tblX.key_part1 = expr1 AND tblX.key_part2 = expr2 AND ... Before performing an index lookup, we determine whether any of the expri values is NULL. If it is, we ...
https://dev.mysql.com/doc/internals/en/optimizer-order-by-clauses.html
For the query: SELECT column1 FROM Table1 ORDER BY 'x'; the optimizer will throw out the ORDER BY clause. For the query: SELECT column1 FROM Table1 ORDER BY column1; the optimizer will use an index on column1, if it exists. For the query: SELECT ...
https://dev.mysql.com/doc/internals/en/optimizer-tracing.html
The interface is provided by a set of optimizer_trace_xxx system variables and the INFORMATION_SCHEMA.OPTIMIZER_TRACE table, but is subject to change. In MySQL 5.6, a new tracing capability was added to the MySQL optimizer.
https://dev.mysql.com/doc/internals/en/other-unsafe-statements.html
Status of this subsection: not started 2009-10-21 INSERT DELAYED LIMIT System tables .
https://dev.mysql.com/doc/internals/en/packet-ERR_Packet.html
This packet signals that an error occurred. It contains a SQL state value if CLIENT_PROTOCOL_41 is enabled. Payload Type Name Description int<1> header [ff] header of the ERR packet int<2> error_code error-code if capabilities & CLIENT_PROTOCOL_41 ...
https://dev.mysql.com/doc/internals/en/parsing-key-information.html
The information in the key is obtained by iterating through the key, which is formatted the same as the definition in table->key_info[index]->key_part[part_num]. Many of the index methods pass a byte array named *key that identifies the index entry ...
https://dev.mysql.com/doc/internals/en/protocoltext-resultset.html
A query like SELECT @@version_comment returns: 01 00 00 01 01|27 00 00 02 03 64 65 66 00 00 00 .....'....def... 11 40 40 76 65 72 73 69 6f 6e 5f 63 6f 6d 6d 65 .@@version_comme 6e 74 00 0c 08 00 1c 00 00 00 fd 00 00 1f 00 00| nt..............
https://dev.mysql.com/doc/internals/en/providing-index-information-to-optimizer.html
In order for indexing to be used effectively, storage engines need to provide the optimizer with information about the table and its indexes. This information is used to choose whether to use an index, and if so, which index to use.