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https://dev.mysql.com/doc/refman/8.0/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/8.0/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/8.0/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/8.0/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/8.0/en/replication-privilege-checks.html
When REQUIRE_ROW_FORMAT is set, you must use row-based binary logging (binlog_format=ROW) on the source server. In MySQL 8.0.18, REQUIRE_ROW_FORMAT is not available, but the use of row-based binary logging for secured replication channels is still ... By default, MySQL replication (including Group Replication) does not carry out privilege checks when transactions that were already accepted by another server are applied on a replica or group ...
https://dev.mysql.com/doc/refman/8.0/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/8.0/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/8.0/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. In ...
https://dev.mysql.com/doc/refman/8.0/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/8.0/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 ...