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https://dev.mysql.com/doc/refman/8.4/en/comparisons-using-subqueries.html
WHERE 'a' = (SELECT column1 FROM t1) MySQL also permits this construct: non_subquery_operand LIKE (subquery) At one time the only legal place for a subquery was on the right side of a comparison, and you might still find some old DBMSs that insist ... The most common use of a subquery is in the form: non_subquery_operand comparison_operator (subquery) Where comparison_operator is one of these operators: = > < >= <= <> != <=> For example: ...
https://dev.mysql.com/doc/refman/8.4/en/concurrent-inserts.html
If there are multiple INSERT statements, they are queued and performed in sequence, concurrently with the SELECT statements. In addition, for those statements a read lock is placed on the selected-from table such that inserts into that table are ...
https://dev.mysql.com/doc/refman/8.4/en/engine-condition-pushdown-optimization.html
An example of such a query, using the table t1 created previously, is shown here: mysql> EXPLAIN -> SELECT * FROM t1 AS x -> LEFT JOIN t1 AS y -> ON x.a=0 AND y.b>=3\G *************************** 1. row *************************** id: 1 select_type: ... This optimization improves the efficiency of direct comparisons between a nonindexed column and a ...
https://dev.mysql.com/doc/refman/8.4/en/enum.html
This means that you can use the following SELECT statement to find rows into which invalid ENUM values were assigned: mysql> SELECT * FROM tbl_name WHERE enum_col=0; The index of the NULL value is NULL. For example, you can retrieve numeric values ... An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation ...
https://dev.mysql.com/doc/refman/8.4/en/forcing-innodb-recovery.html
To investigate database page corruption, you might dump your tables from the database with SELECT ... Serious corruption might cause SELECT * FROM tbl_name statements or InnoDB background operations to unexpectedly exit or assert, or even cause ...
https://dev.mysql.com/doc/refman/8.4/en/fulltext-search-mecab.html
SELECT COUNT(*) FROM articles WHERE MATCH(title,body) AGAINST('データベース管理' IN NATURAL LANGUAGE MODE); For boolean mode search, the search term is converted to a search phrase. SELECT COUNT(*) FROM articles WHERE MATCH(title,body) ...
https://dev.mysql.com/doc/refman/8.4/en/generated-column-index-optimizations.html
You can see this using EXPLAIN: mysql> EXPLAIN SELECT * FROM t1 WHERE f1 + 1 > 9\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: t1 partitions: NULL type: range possible_keys: gc key: gc key_len: 5 ...For example: CREATE TABLE t1 (f1 INT, gc INT AS (f1 + 1) STORED, INDEX (gc)); The generated column, gc, is defined as the expression f1 + ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-changing-group-mode.html
Changing to Single-Primary Mode Use the group_replication_switch_to_single_primary_mode() function to change a group running in multi-primary mode to single-primary mode by issuing: SELECT group_replication_switch_to_single_primary_mode() When you ... This section explains how to change the mode which a group is running in, either single or ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-configuring-consistency-guarantees.html
If there is none, a new one is selected from the list of secondary members. No read skew on read/write transactions, such as this one: > BEGIN; > SELECT x FROM t1; -- x=1 because x=2 is in the backlog; > INSERT x INTO t2; > COMMIT; This query should ... Although the Transaction Synchronization Points section explains that conceptually there are two synchronization points from which you can choose: on read or on write, these terms were a simplification and the terms used in Group Replication are: before and after transaction ...
https://dev.mysql.com/doc/refman/8.4/en/group-replication-enterprise-backup.html
MySQL Enterprise Backup is a commercially-licensed backup utility for MySQL Server, available with MySQL Enterprise Edition. This section explains how to back up and subsequently restore a Group Replication member using MySQL Enterprise Backup. The ...