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https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html
Consider this statement: SELECT /*+ BNL(t2) */ FROM t1, t2; If the optimizer chooses to process t1 first, it applies a Block Nested-Loop join to t2 by buffering the rows from t1 before starting to read from t2. ORDER_INDEX, NO_ORDER_INDEX: Cause ...
https://dev.mysql.com/doc/refman/8.4/en/outer-join-optimization.html
The LEFT JOIN condition is used to decide how to retrieve rows from table B. If there is a row in A that matches the WHERE clause, but there is no row in B that matches the ON condition, an extra B row is generated with all columns set to NULL. For ...MySQL implements an A LEFT JOIN B join_specification as follows: Table B is set to depend on table A and all tables on which A ...
https://dev.mysql.com/doc/refman/8.4/en/partitioning-limitations-partitioning-keys-unique-keys.html
This section discusses the relationship of partitioning keys with primary keys and unique keys. The rule governing this relationship can be expressed as follows: All columns used in the partitioning expression for a partitioned table must be part ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-atom-molecule-events.html
For a table I/O event, there are usually two rows in events_waits_current, not one. For example, a row fetch might result in rows like this: Row# EVENT_NAME TIMER_START TIMER_END ---- ---------- ----------- --------- 1 wait/io/file/myisam/dfile ...
https://dev.mysql.com/doc/refman/8.4/en/replication-rules-examples.html
It is also important to note that the results vary depending on whether the operation is logged using statement-based or row-based binary logging format. With row-based format, DML statements are handled based on the database where the modified ...
https://dev.mysql.com/doc/refman/8.4/en/set.html
Normally, you search for SET values using the FIND_IN_SET() function or the LIKE operator: mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0; mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%'; The first statement finds rows ... A SET is a string object that can have zero or more values, each of which must be chosen from a list of permitted values specified when the table is ...
https://dev.mysql.com/doc/refman/8.4/en/subquery-errors.html
Incorrect number of rows from subquery: ERROR 1242 (ER_SUBSELECT_NO_1_ROW) SQLSTATE = 21000 Message = "Subquery returns more than 1 row" This error occurs for statements where the subquery must return at most one row but returns multiple rows. All ...
https://dev.mysql.com/doc/refman/8.4/en/sys-statement-analysis.html
rows_sent The total number of rows returned by occurrences of the statement. rows_sent_avg The average number of rows returned per occurrence of the statement. rows_examined The total number of rows read from storage engines by occurrences of the ...
https://dev.mysql.com/doc/refman/8.4/en/tracing-example.html
row *************************** QUERY: SELECT SUM(alias2.col_varchar_nokey) AS c1, alias2.pk AS c2 FROM t1 AS alias1 STRAIGHT_JOIN t2 AS alias2 ON alias2.pk = alias1.col_int_key WHERE alias1.pk GROUP BY c2 ORDER BY alias1.col_int_key, alias2.pk This ...Now we can examine the trace, whose first column (QUERY), containing the original statement to be traced, is shown here: SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE\G ...
https://dev.mysql.com/doc/refman/8.4/en/using-spatial-indexes.html
| +-----+---------------------------------------------------------------+ 20 rows in set (0.00 sec) Use EXPLAIN to check the way this query is executed: mysql> SET @poly = -> 'Polygon((30000 15000, 31000 15000, 31000 16000, 30000 16000, 30000 ...