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The FOREIGN KEY constraint also prevents invalid data from being inserted into the foreign key column, because it has to be one of the values contained in the table it points to. Let's say we have these two tables in our database. You have to either drop the child tables before removing the parent table, or remove foreign key constraints.
Workspace SWITCH TO dbo. Friday, March 22, 2013 - 1:15:06 PM - David I get about 14 roes returned. I don't get any output. I have sysadmin rights to the box and databases.
How to create a SQL Server foreign key - ON UPDATE CASCADE, SET NULL, or SET DEFAULT cannot be defined if an INSTEAD OF trigger ON UPDATE already exists on the table that is being altered. To make matters more complicated, the databases I support can harness various schema depending upon which build was released for a given set of customers.
Constraint names must follow the rules for , except that the name cannot start with a number sign. PRIMARY KEY Is a constraint that enforces entity integrity for a specified column or columns by using a unique index. Only one PRIMARY KEY constraint can be created for each table. UNIQUE Is a constraint that provides entity integrity for a specified column or columns by using a unique index. CLUSTERED NONCLUSTERED Specifies that a clustered or nonclustered index is created for the PRIMARY KEY or UNIQUE constraint. PRIMARY KEY constraints default to CLUSTERED. UNIQUE constraints default to NONCLUSTERED. If a clustered constraint or index already exists on a table, CLUSTERED cannot be specified. If a clustered constraint or index already exists on a table, PRIMARY KEY constraints default to NONCLUSTERED. Columns that are of the ntext, text, varchar max , nvarchar max , varbinary max , xml, or image data types cannot be specified as columns for an index. The default is ASC. User-specified fillfactor values can be from 1 through 100. If a value is not specified, the default is 0. Other index options can be specified in the clause of ALTER TABLE. Specifies the storage location of the index created for the constraint. If filegroup is specified, the index is created in the named filegroup. If ON is specified when a clustered index is added for a PRIMARY KEY or UNIQUE constraint, the whole table is moved to the specified filegroup when the clustered index is created. This is the default setting. FOREIGN KEY REFERENCES Is a constraint that provides referential integrity for the data in the column. FOREIGN KEY constraints require that each value in the column exist in the specified column in the referenced table. ON DELETE NO ACTION CASCADE SET NULL SET DEFAULT Specifies what action happens to rows in the table that is altered, if those rows have a referential relationship and the referenced row is deleted from the parent table. The default is NO ACTION. NO ACTION The SQL Server Database Engine raises an error and the delete action on the row in the parent table is rolled back. CASCADE Corresponding rows are deleted from the referencing table if that row is deleted from the parent table. SET NULL All the values that make up the foreign key are set to NULL when the corresponding row in the parent table is deleted. For this constraint to execute, the foreign key columns must be nullable. SET DEFAULT All the values that comprise the foreign key are set to their default values when the corresponding row in the parent table is deleted. For this constraint to execute, all foreign key columns must have default definitions. If a column is nullable and there is no explicit default value set, NULL becomes the implicit default value of the column. Do not specify CASCADE if the table will be included in a merge publication that uses logical records. For more information about logical records, see. ON DELETE CASCADE cannot be defined if an INSTEAD OF trigger ON DELETE already exists on the table that is being altered. For example, in the AdventureWorks2012 database, the ProductVendor table has a referential relationship with the Vendor table. VendorID foreign key references the Vendor. If a DELETE statement is executed on a row in the Vendor table and an ON DELETE CASCADE action is specified for ProductVendor. VendorID, the Database Engine checks for one or more dependent rows in the ProductVendor table. If any exist, the dependent rows in the ProductVendor table will be deleted, in addition to the row referenced in the Vendor table. Conversely, if NO ACTION is specified, the Database Engine raises an error and rolls back the delete action on the Vendor row when there is at least one row in the ProductVendor table that references it. ON UPDATE NO ACTION CASCADE SET NULL SET DEFAULT Specifies what action happens to rows in the table altered when those rows have a referential relationship and the referenced row is updated in the parent table. The default is NO ACTION. NO ACTION The Database Engine raises an error, and the update action on the row in the parent table is rolled back. CASCADE Corresponding rows are updated in the referencing table when that row is updated in the parent table. SET NULL All the values that make up the foreign key are set to NULL when the corresponding row in the parent table is updated. For this constraint to execute, the foreign key columns must be nullable. SET DEFAULT All the values that make up the foreign key are set to their default values when the corresponding row in the parent table is updated. For this constraint to execute, all foreign key columns must have default definitions. If a column is nullable, and there is no explicit default value set, NULL becomes the implicit default value of the column. Do not specify CASCADE if the table will be included in a merge publication that uses logical records. For more information about logical records, see. ON UPDATE CASCADE, SET NULL, or SET DEFAULT cannot be defined if an INSTEAD OF trigger ON UPDATE already exists on the table that is being altered. For example, in the AdventureWorks2012 database, the ProductVendor table has a referential relationship with the Vendor table. VendorID foreign key references the Vendor. If an UPDATE statement is executed on a row in the Vendor table and an ON UPDATE CASCADE action is specified for ProductVendor. VendorID, the Database Engine checks for one or more dependent rows in the ProductVendor table. If any exist, the dependent row in the ProductVendor table will be updated, as well as the row referenced in the Vendor table. Conversely, if NO ACTION is specified, the Database Engine raises an error and rolls back the update action on the Vendor row when there is at least one row in the ProductVendor table that references it. NOT FOR REPLICATION Applies to: SQL Server 2008 through SQL Server 2017. Can be specified for FOREIGN KEY constraints and CHECK constraints. If this clause is specified for a constraint, the constraint is not enforced when replication agents perform insert, update, or delete operations. CONNECTION Specifies the pair of node tables that the given edge constraint is allowed to connect. DEFAULT Specifies the default value for the column. DEFAULT definitions can be used to provide values for a new column in the existing rows of data. DEFAULT definitions cannot be added to columns that have a timestamp data type, an IDENTITY property, an existing DEFAULT definition, or a bound default. If the column has an existing default, the default must be dropped before the new default can be added. To maintain compatibility with earlier versions of SQL Server, a constraint name can be assigned to a DEFAULT. FOR column Specifies the column associated with a table-level DEFAULT definition. If the column being added does not allow NULLS, for existing rows, the column's value will always be set to the value given in the DEFAULT constant expression. Starting in SQL Server 2012 this may be a meta data operation. If this is used when the related column isn't also being added then it has no effect. CHECK Is a constraint that enforces domain integrity by limiting the possible values that can be entered into a column or columns. The expression cannot reference an alias data type. Remarks When FOREIGN KEY or CHECK constraints are added, all existing data is verified for constraint violations unless the WITH NOCHECK option is specified. If any violations occur, ALTER TABLE fails and an error is returned. When a new PRIMARY KEY or UNIQUE constraint is added to an existing column, the data in the column or columns must be unique. If duplicate values are found, ALTER TABLE fails. The WITH NOCHECK option has no effect when PRIMARY KEY or UNIQUE constraints are added. Each PRIMARY KEY and UNIQUE constraint generates an index. The number of UNIQUE and PRIMARY KEY constraints cannot cause the number of indexes on the table to exceed 999 nonclustered indexes and 1 clustered index. Foreign key constraints do not automatically generate an index. However, foreign key columns are frequently used in join criteria in queries by matching the column or columns in the foreign key constraint of one table with the primary or unique key column or columns in the other table. An index on the foreign key columns enables the Database Engine to quickly find related data in the foreign key table. Examples For examples, see.
ON UPDATE CASCADE, SET NULL, or SET DEFAULT cannot be defined if an INSTEAD OF trigger ON UPDATE already exists on the table that is being altered. Thursday, March 21, 2013 - 5:10:22 PM - Greg Robidoux David - one more question. Constraint names must follow the rules forexcept that the name cannot start with a number sign. Q1 delete from dbo. And when i do that i get the Following error. Wednesday, June 12, 2013 - 2:12:36 PM - Ken Hi Greg, Did you get this issue figured out with David. For this foreign key, we have specified the ON DELETE CASCADE clause which tells SQL Server to delete the corresponding records in the child table when the data in the parent table is deleted.
