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https://dev.mysql.com/doc/refman/8.0/en/create-table-check-constraints.html
Prior to MySQL 8.0.16, CREATE TABLE permits only the following limited version of table CHECK constraint syntax, which is parsed and ignored: CHECK (expr) As of MySQL 8.0.16, CREATE TABLE permits the core features of table and column CHECK ...If ...
https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html
MySQL supports foreign keys, which permit cross-referencing related data across tables, and foreign key constraints, which help keep the related data consistent. If the CONSTRAINT symbol clause is not defined, or a symbol is not included following ...A foreign key relationship involves a parent table that holds the initial column values, and a child table with column values that reference the parent column ...
https://dev.mysql.com/doc/refman/8.0/en/constraint-foreign-key.html
Foreign keys let you cross-reference related data across tables, and foreign key constraints help keep this spread-out data consistent. Since MySQL does not support deferred constraint checking, NO ACTION is treated as RESTRICT. For the exact ...
https://dev.mysql.com/doc/refman/8.0/en/constraint-primary-key.html
Normally, errors occur for data-change statements (such as INSERT or UPDATE) that would violate primary-key, unique-key, or foreign-key constraints. If you are using a transactional storage engine such as InnoDB, MySQL automatically rolls back the ...
https://dev.mysql.com/doc/refman/8.0/en/constraints.html
Because of this, constraint handling is a bit different in MySQL than in other DBMSs. The following sections describe how MySQL Server handles different types of constraints. MySQL enables you to work both with transactional tables that permit ...
https://dev.mysql.com/doc/refman/8.0/en/constraint-enum.html
Unless strict mode is disabled (not recommended, but see Section 7.1.11, “Server SQL Modes”), the definition of a ENUM or SET column acts as a constraint on values entered into the column. ENUM and SET columns provide an efficient way to define ...
https://dev.mysql.com/doc/refman/8.0/en/constraint-invalid-data.html
Older versions of MySQL employed the forgiving behavior by default; for a description of this behavior, see Constraints on Invalid Data. By default, MySQL 8.0 rejects invalid or improper data values and aborts the statement in which they occur. It ...
https://dev.mysql.com/doc/refman/8.0/en/alter-table.html
| ADD [CONSTRAINT [symbol]] UNIQUE [INDEX | KEY] [index_name] [index_type] (key_part,...) [index_option] ... Foreign Keys and Other Constraints The FOREIGN KEY and REFERENCES clauses are supported by the InnoDB and NDB storage engines, which ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-referential-constraints-table.html
The REFERENTIAL_CONSTRAINTS table has these columns: CONSTRAINT_CATALOG The name of the catalog to which the constraint belongs. CONSTRAINT_SCHEMA The name of the schema (database) to which the constraint belongs. UNIQUE_CONSTRAINT_CATALOG The name ...The possible values are CASCADE, SET NULL, SET DEFAULT, RESTRICT, NO ...
https://dev.mysql.com/doc/refman/8.0/en/glossary.html
For example, for a column with a unique constraint, the number of different values is equal to the number of rows in the table. See Also column, composite index, index, index hint, persistent statistics, random dive, selectivity, unique constraint.