Note:As with other constraints, naming aFOREIGN KEYconstraint usingCONSTRAINT constraint_nameis optional. But doing so makes it easier to make changes to or delete the constraint. This is especially helpful when defining multiple constraints. Recommended Readings:...
PostgreSQL foreign key constraint syntax The following illustrates a foreign key constraint syntax: [CONSTRAINT fk_name] FOREIGN KEY(fk_columns) REFERENCES parent_table(parent_key_columns) [ON DELETE delete_action] [ON UPDATE update_action] In this syntax: First, specify the name for the foreign...
Oracle foreign key constraint syntax Oracle allows you to create, add, drop, disable, and enable a foreign key constraint. Create a foreign key constraint The following statement illustrates the syntax of creating a foreign key constraint when you create a table: ...
OrderID intNOTNULLPRIMARYKEY, OrderNumber intNOTNULL, PersonID intFOREIGNKEYREFERENCESPersons(PersonID) ); To allow naming of aFOREIGN KEYconstraint, and for defining aFOREIGN KEYconstraint on multiple columns, use the following SQL syntax:
If the syntax for creating a MySQL table instead used the following reserved words, then the confusion would disappear: FOREIGN KEY CONSTRAINT fk1_rule_child_column FOREIGN KEY INDEX (fk_bst_child_to_parent_column) REFERENCES parent_table (parent_column) Furthermore, since MySQL always creates ...
CREATE TABLE b(for_key INT REFERENCES a(not_key)); MariaDB simply parses it without returning any error or warning, for compatibility with other DBMS's. However, only the syntax described below creates foreign keys. FromMariaDB 10.5, MariaDB will attempt to apply the constraint. See theExa...
You can drop a foreign key constraint using the followingALTER TABLEsyntax: ALTER TABLEtbl_nameDROP FOREIGN KEYfk_symbol; If theFOREIGN KEYclause defined aCONSTRAINTname when you created the constraint, you can refer to that name to drop the foreign key constraint. Otherwise, a constraint name ...
在truncate表的时候报告以下错误,意思是有的表有外键关联,不能清空。 SQLSTATE[42000]: Syntax error or access violation: 1701 Cannot truncate a table referenced in a foreign key constraint (alerting.datapoints, CONSTRAINT datapoints_sensor_id_foreign FOREIGN KEY (sensor_id) REFERENCES alerting.sensors (...
Like the optional parentheses that can enclose various ALTER TABLE ADD CONSTRAINT syntax options, the parentheses enclosing the "Foreign key constraint in NOVALIDATE mode" syntax segment are optional. The next statement has the same effect as the previousNOVALIDATEexample: ...
InnoDBsupports foreign key constraints. The syntax for a foreign key constraint definition inInnoDBlooks like this: [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name, ...) REFERENCEStbl_name(index_col_name,...) [ON DELETEreference_option] ...