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https://dev.mysql.com/doc/refman/5.7/en/show-slave-hosts.html
Statement output includes this column only if the source server is started with the --show-slave-auth-info option. Statement output includes this column only if the source server is started with the --show-slave-auth-info option. A zero in this ...
https://dev.mysql.com/doc/refman/5.7/en/string-comparison-functions.html
For example, it can be specified as a string expression or table column. In the latter case, the column must be defined as one of the MySQL string types (see Section 11.3, “String Data Types”). Note Aggregate queries involving NOT LIKE ... Table ...
https://dev.mysql.com/doc/refman/5.7/en/subqueries.html
Here is an example of a subquery: SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2); In this example, SELECT * FROM t1 ... is the outer query (or outer statement), and (SELECT column1 FROM t2) is the subquery. All subquery forms and ...
https://dev.mysql.com/doc/refman/5.7/en/subquery-errors.html
Consider the following example: SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2); If SELECT column1 FROM t2 returns just one row, the previous query works. Incorrect number of rows from subquery: ERROR 1242 (ER_SUBSELECT_NO_1_ROW) SQLSTATE ...
https://dev.mysql.com/doc/refman/5.7/en/subquery-materialization.html
Assume that where_condition involves columns only from t2 and not t1 so that the subquery is noncorrelated. The optimizer uses materialization to enable more efficient subquery processing. Materialization speeds up query execution by generating a ...
https://dev.mysql.com/doc/refman/5.7/en/subquery-optimization-with-exists.html
In EXPLAIN output, the fallback shows up as Full scan on NULL key in the Extra column: mysql> EXPLAIN SELECT t1.col1, t1.col1 IN (SELECT t2.key1 FROM t2 WHERE t2.col2=t1.col2) FROM t1\G *************************** 1. To help the query optimizer ...
https://dev.mysql.com/doc/refman/5.7/en/table-locking.html
MySQL uses table locking (instead of page, row, or column locking) for all storage engines except InnoDB. Splitting table contents into separate tables may help, by allowing queries to run against columns in one table, while updates are confined to ... InnoDB tables use row-level locking so that multiple sessions and applications can read from and write to the same table simultaneously, without making each other wait or producing inconsistent ...
https://dev.mysql.com/doc/refman/5.7/en/user-variables.html
(This is the same coercibility as for table column values.) Hexadecimal or bit values assigned to user variables are treated as binary strings. The following example illustrates this: mysql> SET @a='test'; mysql> SELECT @a,(@a:=20) FROM tbl_name; ...
https://dev.mysql.com/doc/refman/5.7/en/using-explain.html
Note EXPLAIN can also be used to obtain information about the columns in a table. EXPLAIN tbl_name is synonymous with DESCRIBE tbl_name and SHOW COLUMNS FROM tbl_name. For more information, see Section 13.8.1, “DESCRIBE Statement”, and Section ... The EXPLAIN statement provides information about how MySQL executes statements: EXPLAIN works with SELECT, DELETE, INSERT, REPLACE, and UPDATE ...
https://dev.mysql.com/doc/refman/5.7/en/adding-collation-choosing-id.html
The collation ID that you choose appears in these contexts: The ID column of the Information Schema COLLATIONS table. To add a collation, you must choose an ID value that is not currently used. The range of IDs from 1024 to 2047 is reserved for ...