Can only primary key be foreign key
WebApr 9, 2015 · 2 Answers Sorted by: 16 A foreign key can reference any field defined as unique. If that unique field is itself defined as a foreign key, it makes no difference. A foreign key is just to enforce referential integrity. Making a field a foreign key doesn't change the field itself in any way. WebFeb 15, 2015 · Yes, you can reference a column (or columns) governed by either a primary key constraint or a unique constraint. The problem with your table "studentsprofilepic" is …
Can only primary key be foreign key
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WebMar 11, 2024 · 11 Answers. Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not … WebJun 10, 2012 · Primary keys always need to be unique, foreign keys need to allow non-unique values if the table is a one-to-many relationship. It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not …
WebApr 23, 2024 · Yes, of course. It's common for a subset of a primary key to be a foreign key. Any many-to-many table does this for instance. In your case: CREATE TABLE ConcertDetails ( ConcertDate DATE NOT NULL, ConcertID INT NOT NULL, PRIMARY KEY (ConcertDate, ConcertID), FOREIGN KEY (ConcertID) REFERENCES Concerts … WebAnswer: primary key:- A primary contains unique and notnull.it means. a primary key column does not contain null values and. duplicates.A table containe only one primary key.using this. we can access the data from table easily. foreign key:-a fk can contain duplicate values but it not. contain null values.using fk to establish relationship.
WebAug 26, 2013 · It is perfectly fine to use a foreign key as the primary key if the table is connected by a one-to-one relationship, not a one-to-many relationship. A FOREIGN … WebNo. When you create a foreign key, the key that you "point to" in the other table must be a UNIQUE or PRIMARY KEY constraint. You cannot establish a foreign key that points to a column that allow duplicate values.
WebNov 11, 2011 · If no, then the PK should be non-clustered. To give an example, consider a sales facts table. Each entry has an ID that is the primary key. But the vast majority of queries ask for data between a date and another date, therefore the best clustered index key would be the sales date, not the ID.
WebNov 22, 2012 · Yes, you can make one without a Primary Key (or, another option is a Compound Primary Key - making the two references a unique pair, and using that as the unique identifying key - but even this isn't necessary (note: just because it "isn't necessary" doesn't mean it isn't "good practice"; it wouldn't generally be a good idea to have several … incarnate word softball rosterWebOct 28, 2024 · A Computer Science portal for geeks. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. incarnate word softballWebPrimary Key: It is unique column in every table in a database It can ONLY accept;-nonduplicate values-cannot be NULL Foreign Key: It is a column that comes from a different table and using Foreign key tables are related each other It is the primary key of another table It can be duplicate or null for another table Unique Key: Only unique value ... incarnate word softball coachWebIf you mean "can column (or set of columns) be a primary key as well as a foreign key in the same table?", the answer, in my view, is a no; it seems meaningless. However, the following definition succeeds in SQL Server! create table t1 (c1 int not null primary key foreign key references t1 (c1)) in city printsWebOct 14, 2013 · Yes, you might do so. But you need to be careful as foreign keys can have NULL values whereas Primary can't. incarnate word st louisWebMake the primary key id, a unique key on (id,type), the child tables' foreign key be on (id, type), and put a CHECK constraint on each child table to only have the correct type. Or, if you database does global check constraints (and without huge speed penalty), you can of course just do a NOT EXISTS check. – derobert Oct 25, 2011 at 19:14 in city relocationWebSep 6, 2014 · It should be UNIQUE because a primary key identifies rows in a table so 2 different row should not have the same key. In addition a primary key may be used a FOREIGN KEY in other tables and that's why it cannot be NULL so that the other table can fin the rows in the referenced table. For example: in city pics