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Can a foreign key references composite primary key?
The foreign key can not refer to part of composite primary key of other table. Because it is supposed to be one-to-one relationship and if you refer just part of primary-key, there might be more than one parent record available, which is neither allowed nor possible.
Can a foreign key reference two tables?
A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. A foreign key acts as a cross-reference between tables in that it references the primary key or unique key columns of another table, and thus establishes a link between them.
Can 2 foreign keys make a composite key?
When you use the multiple-column constraint format, you can create a composite key. In other words, if the primary key is a set of columns (a composite key), then the foreign key also must be a set of columns that corresponds to the composite key.
Can we join two tables with primary foreign key relation?
A primary key is not required. A foreign key is not required either. You can construct a query joining two tables on any column you wish as long as the datatypes either match or are converted to match. No relationship needs to explicitly exist.
How to set up primary and foreign keys referencing two?
Msg 142, Level 15, State 2, Line 2 Incorrect syntax for definition of the ‘TABLE’ constraint. Please advise. The actual error message you are getting is because your CREATE TABLE statement is malformed as you cannot have a foreign key refer to more than one table.
Can a composite foreign key be used as a primary key?
You can create a composite foreign key just as you would create a single foreign key, except that instead of specifying just one column, you provide the name of two or more columns, separated by a comma. Here’s an example of a database using a composite foreign key (and a composite primary key).
How to create FK relationship with composite primary keys?
Since Table2 has a composite primary key (FileID, FileType), then any reference to it must also include both columns. Unless you have a unique constraint/index on the Table2.FileID field (but if so: why isn’t this the PK??), you cannot create a FK relationship to only parts of the PK on the target table – just can’t do it.
How to add a foreign key to Table1?
If the rows in Table1 only ever relate to one type of File (e.g. FileType ‘ABC’), then you can add FileType to Table1 as a computed column: Which you can then use in the Foreign Key.