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https://dev.mysql.com/doc/refman/8.0/en/ansi-diff-foreign-keys.html
In an SQL statement that inserts, deletes, or updates many rows, foreign key constraints (like unique constraints) are checked row-by-row. However, MySQL does not enforce a requirement that the referenced columns be UNIQUE or be declared NOT NULL. A ...For example, if you define a RESTRICT type constraint, and there is a child row with several parent rows, InnoDB does not permit the deletion of any of the parent ...
https://dev.mysql.com/doc/refman/8.0/en/converting-tables-to-innodb.html
If you have UNIQUE constraints on secondary keys, you can speed up a table import by turning off the uniqueness checks temporarily during the import operation: SET unique_checks=0; ... SET unique_checks=1; For big tables, this saves disk I/O because ... If you have MyISAM tables that you want to convert to InnoDB for better reliability and scalability, review the following guidelines and tips before ...
https://dev.mysql.com/doc/refman/8.0/en/create-table-select.html
You can precede the SELECT by IGNORE or REPLACE to indicate how to handle rows that duplicate unique key values. With IGNORE, rows that duplicate an existing row on a unique key value are discarded. With REPLACE, new rows replace rows that have the ... You can create one table from another by adding a SELECT statement at the end of the CREATE TABLE statement: CREATE TABLE new_tbl [AS] SELECT * FROM orig_tbl; MySQL creates new columns for all elements in the ...
https://dev.mysql.com/doc/refman/8.0/en/group-replication-requirements.html
Every table that is to be replicated by the group must have a defined primary key, or primary key equivalent where the equivalent is a non-null unique key. Such keys are required as a unique identifier for every row within a table, enabling the ...
https://dev.mysql.com/doc/refman/8.0/en/innodb-persistent-stats.html
The number of columns in the table's primary key is also important to consider, as primary key columns are appended to each nonunique index. Note For nonunique indexes, InnoDB appends the columns of the primary key. Only two columns are defined for ... The persistent optimizer statistics feature improves plan stability by storing statistics to disk and making them persistent across server restarts so that the optimizer is more likely to make consistent choices each time for a given ...
https://dev.mysql.com/doc/refman/8.0/en/insert.html
INSERT with an ON DUPLICATE KEY UPDATE clause enables existing rows to be updated if a row to be inserted would cause a duplicate value in a UNIQUE index or PRIMARY KEY. (This is not necessarily the number of rows actually inserted because ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-limitations-syntax.html
Using nullable columns in unique keys and primary keys means that queries using these columns are handled as full table scans. A BIT column cannot be a primary key, unique key, or index, nor can it be part of a composite primary key, unique key, or ... Some SQL statements relating to certain MySQL features produce errors when used with NDB tables, as described in the following list: Temporary ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-option-tables.html
ndb-deferred-constraints: Specifies that constraint checks on unique indexes (where these are supported) should be deferred until commit time. Ndb_api_uk_op_count: Number of operations based on or using unique keys by this MySQL Server (SQL node).
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-what-is-new.html
Work done in NDB 8.0.20 allows many outer joins and semijoins, and not only those using a primary key or unique key lookup, to be pushed down to the data nodes (see Section 10.2.1.5, “Engine Condition Pushdown Optimization”). --remap-column can ... The following sections describe changes in the implementation of MySQL NDB Cluster in NDB Cluster 8.0 through 8.0.41, as compared to earlier release ...
https://dev.mysql.com/doc/refman/8.0/en/mysql-shell-tutorial-javascript-indexes-create.html
Add a Nonunique Index To create a nonunique index, pass an index name and the index information to the createIndex() method. Add a Unique Index To create a unique index, pass an index name, the index definition, and the index type “unique” to ...