How do I drop a foreign key constraint only if it exists in sql server?
2009年1月27日 · IF (OBJECT_ID('dbo.FK_ConstraintName', 'F') IS NOT NULL) BEGIN ALTER TABLE dbo.TableName DROP CONSTRAINT FK_ConstraintName END If you need to drop another type of constraint, these are the applicable codes to pass into the OBJECT_ID() function in the second parameter position:
Can a foreign key be NULL and/or duplicate? - Stack Overflow
2017年3月11日 · Most FKs are for a one to many relationship and that is what you get from a FK without adding a further constraint on the field. So you have an order table and the order details table for instance. If the customer orders ten items at one time, he has one order and ten order detail records that contain the same orderID as the FK.
What is a proper naming convention for MySQL FKs?
2010年2月10日 · user_id in messages table is a fk field so it has to make clear which id is (user_id). a fully-self-explaining naming convention, in my opinion, could be: fk_[referencing table name]_[referencing field name]_[referenced table name]_[referenced field name] i.e.: `fk_messages_user_id_users_id`
sql - Foreign Keys vs Joins - Stack Overflow
@Kangkan creating FK have nothing to do with performance FK != Indexes. There are DBMS automatic creates a index in the FK creation but most don't. Joins don't need FK please refer to excellent Daniel answer. Maybe OP is confused by ORM frameworks –
How to find foreign key dependencies in SQL Server?
2009年5月29日 · select fk_table = fk.table_name, fk_column = cu.column_name, pk_table = pk.table_name, pk_column = pt.column_name, constraint_name = c.constraint_name from information_schema.referential_constraints c inner join information_schema.table_constraints fk on c.constraint_name = fk.constraint_name inner join information_schema.table_constraints pk ...
sql - Foreign Key to non-primary key - Stack Overflow
2013年8月26日 · Consider the case of a Customer table with a SSN column (and a dumb primary key), and a Claim table that also contains a SSN column (populated by business logic from the Customer data, but no FK exists). The design is flawed, but has been in use for several years, and three different applications have been built on the schema.
foreign key constraint naming scheme - Stack Overflow
FK_task_user This gives you an 'at a glance' view of which tables are involved in the key, so it makes it easy to see which tables a particular one (the first one named) depends on (the second one named). In this scenario the complete set of keys …
Does a foreign key automatically create an index?
However, it makes a lot of sense to index all the columns that are part of any foreign key relationship. An FK-relationship will often need to look up a relating table and extract certain rows based on a single value or a range of values. So it makes good sense to index any columns involved in an FK, but an FK per se is not an index.
List of foreign keys and the tables they reference in Oracle DB
2019年3月19日 · WITH reference_view AS (SELECT a.owner, a.table_name, a.constraint_name, a.constraint_type, a.r_owner, a.r_constraint_name, b.column_name FROM dba_constraints a, dba_cons_columns b WHERE a.owner = b.owner AND a.constraint_name = b.constraint_name AND constraint_type = 'R'), constraint_view AS (SELECT a.owner a_owner, a.table_name, …
How do I drop a foreign key in SQL Server? - Stack Overflow
2008年9月18日 · The object 'Company_CountryID_FK' is dependent on column 'CountryID'. Msg 4922, Level 16, State 9, Line 2 ALTER TABLE DROP COLUMN CountryID failed because one or more objects access this column. I have tried this, yet it does not seem to work: alter table company drop foreign key Company_CountryID_FK; alter table company drop column CountryID;