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https://dev.mysql.com/doc/refman/8.0/en/subqueries.html
All subquery forms and operations that the SQL standard requires are supported, as well as a few features that are MySQL-specific. Here is an example of a subquery: SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2); In this example, SELECT * ...
https://dev.mysql.com/doc/refman/8.0/en/subquery-restrictions.html
FROM t...) AS dt ...); Here the result from the derived table is materialized as a temporary table, so the relevant rows in t have already been selected by the time the update to t takes place. Row comparison operations are only partially supported: ... In general, you cannot modify a table and select from the same table in a ...
https://dev.mysql.com/doc/refman/8.0/en/sys-ps-trace-statement-digest.html
| +-----------------------------------------------------------------+ 1 row in set (9.17 sec) +------------------------------------------+-----------+ | event_name | latency | +------------------------------------------+-----------+ | stage/sql/init ... Traces all Performance Schema instrumentation for a specific statement ...
https://dev.mysql.com/doc/refman/8.0/en/time-zone-support.html
The following query determines whether the table that contains time zone names has any rows: mysql> SELECT COUNT(*) FROM mysql.time_zone_name; +----------+ | COUNT(*) | +----------+ | 0 | +----------+ A count of zero indicates that the table is ...
https://dev.mysql.com/doc/refman/8.0/en/create-view.html
The WITH CHECK OPTION clause can be given to constrain inserts or updates to rows in tables referenced by the view. For a view to be updatable, there must be a one-to-one relationship between the rows in the view and the rows in the underlying table. The WITH CHECK OPTION clause can be given for an updatable view to prevent inserts or updates to rows except those for which the WHERE clause in the select_statement is ...
https://dev.mysql.com/doc/refman/8.0/en/group-replication-requirements.html
Such keys are required as a unique identifier for every row within a table, enabling the system to determine which transactions conflict by identifying exactly which rows each transaction has modified. Group Replication relies on the row-based ...
https://dev.mysql.com/doc/refman/8.0/en/index-extensions.html
row *************************** id: 1 select_type: SIMPLE table: t1 type: ref possible_keys: PRIMARY,k_d key: k_d key_len: 4 ref: const rows: 5 Extra: Using where; Using index When the optimizer takes index extensions into account, it treats k_d as ... InnoDB automatically extends each secondary index by appending the primary key columns to ...
https://dev.mysql.com/doc/refman/8.0/en/index-hints.html
The USE INDEX (index_list) hint tells MySQL to use only one of the named indexes to find rows in the table. In other words, a table scan is used only if there is no way to use one of the named indexes to find rows in the table. To affect only the ...
https://dev.mysql.com/doc/refman/8.0/en/index-merge-optimization.html
The Index Merge access method retrieves rows with multiple range scans and merges their results into one. If all columns used in the query are covered by the used indexes, full table rows are not retrieved (EXPLAIN output contains Using index in ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-information-schema-understanding-innodb-locking.html
When a transaction updates a row in a table, or locks it with SELECT FOR UPDATE, InnoDB establishes a list or queue of locks on that row. If a second transaction wants to update a row or lock a table already locked by a prior transaction in an ...