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https://dev.mysql.com/doc/refman/5.7/en/show-triggers.html
SHOW TRIGGERS [{FROM | IN} db_name] [LIKE 'pattern' | WHERE expr] SHOW TRIGGERS lists the triggers currently defined for tables in a database (the default database unless a FROM clause is given). This statement returns results only for databases ...
https://dev.mysql.com/doc/refman/5.7/en/subquery-optimization-with-exists.html
row *************************** id: 2 select_type: DEPENDENT SUBQUERY table: t2 type: ref_or_null possible_keys: maybe_null_key key: maybe_null_key key_len: 5 ref: func rows: 2 Extra: Using where; Using index ... Triggered equalities can be used by ... Certain optimizations are applicable to comparisons that use the IN (or =ANY) operator to test subquery ...
https://dev.mysql.com/doc/refman/5.7/en/subquery-restrictions.html
In general, you cannot modify a table and select from the same table in a subquery. FROM t ...); Exception: The preceding prohibition does not apply if for the modified table you are using a derived table and that derived table is materialized ...
https://dev.mysql.com/doc/refman/5.7/en/sys-metrics.html
The metric type determines the source from which the name is taken: For global status variables: The VARIABLE_NAME column of the global_status table For InnoDB metrics: The NAME column of the INNODB_METRICS table For other metrics: A view-provided ... This view summarizes MySQL server metrics to show variable names, values, types, and whether they are ...
https://dev.mysql.com/doc/refman/5.7/en/sys-sys-get-config.html
Given a configuration option name, returns the option value from the sys_config table, or the provided default value (which may be NULL) if the option does not exist in the table. If so, the routine uses the variable value without reading the ...If ...
https://dev.mysql.com/doc/refman/5.7/en/triggers.html
A trigger is a named database object that is associated with a table, and that activates when a particular event occurs for the table. Some uses for triggers are to perform checks of values to be inserted into a table or to perform calculations on ...For example, rows can be inserted by INSERT or LOAD DATA statements, and an insert trigger activates for each inserted ...
https://dev.mysql.com/doc/refman/5.7/en/using-explain.html
That is, MySQL explains how it would process the statement, including information about how tables are joined and in which order. With the help of EXPLAIN, you can see where you should add indexes to tables so that the statement executes faster by ... 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/show-warnings.html
Warnings are generated for DML statements such as INSERT, UPDATE, and LOAD DATA as well as DDL statements such as CREATE TABLE and ALTER TABLE. The ALTER TABLE statement produces three warning messages (strict SQL mode is disabled for the example to ...mysql> CREATE TABLE t1 (a TINYINT NOT NULL, b CHAR(4)); Query OK, 0 rows affected (0.05 sec) mysql> INSERT INTO t1 VALUES(10,'mysql'), (NULL,'test'), (300,'xyz'); Query OK, 3 rows affected, 3 warnings (0.00 sec) Records: 3 Duplicates: 0 Warnings: 3 mysql> SHOW WARNINGS\G ...
https://dev.mysql.com/doc/refman/5.7/en/column-indexes.html
Note Prefix limits are measured in bytes, whereas the prefix length in CREATE TABLE, ALTER TABLE, and CREATE INDEX statements is interpreted as number of characters for nonbinary string types (CHAR, VARCHAR, TEXT) and number of bytes for binary ...
https://dev.mysql.com/doc/refman/5.7/en/constraint-foreign-key.html
MySQL supports ON UPDATE and ON DELETE foreign key references in CREATE TABLE and ALTER TABLE statements. Foreign keys let you cross-reference related data across tables, and foreign key constraints help keep this spread-out data consistent. MySQL ...The available referential actions are RESTRICT (the default), CASCADE, SET NULL, and NO ...