What does references mean in mysql

REFERENCES is the keyword to create foreign key constraints in MySQL, ensuring that the values ​​in the child table exist in the corresponding records in the parent table. Its functions include: ensuring data consistency. Enforce a one-to-many or many-to-many relationship. Simplify queries and joins.

REFERENCES in MySQL

What are REFERENCES?

REFERENCES is the keyword used to create foreign key constraints in MySQL. Foreign key constraints ensure that values ​​in the child table (referring table) have corresponding records in the parent table (referenced table).

Syntax of REFERENCES

<code class="sql">ALTER TABLE 子表 ADD CONSTRAINT 外键名 FOREIGN KEY (子表字段) REFERENCES 父表 (父表字段);</code>

Example

Suppose we have two tables: Ordersand product, where the foreign key product_id of the order table refers to the id primary key of the product table.

<code class="sql">ALTER TABLE 订单 ADD CONSTRAINT FK_product FOREIGN KEY (product_id) REFERENCES 产品 (id);</code>

The role of REFERENCES

• Ensure data consistency: REFERENCES constraints prevent inserts, updates, or deletions in child tables from causing data Inconsistency.
• Forcing one-to-many or many-to-many relationships: REFERENCES constraints allow one-to-many or many-to-many relationships to be defined between tables, which helps ensure data integrity .
• Simplify queries and joins: REFERENCES constraints make it easier to query and join between tables.

Notes

• The columns in the parent table must be primary keys or unique indexes.
• The referenced column in the child table must have the same data type as that in the parent table.
• When deleting, updating, or modifying reference fields in both the parent table and the child table, the data in the related tables may be affected.

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