Can a table have 3 primary keys?
A table can only ever have a one primary key. It is not possible to create a table with two different primary keys. You can create a table with two different unique indexes (which are much like a primary key) but only one primary key can exist.
Can a table have multiple primary keys can it have multiple foreign keys?
A FOREIGN KEY constraint can only point to one table and each table can only have one PRIMARY KEY constraint. Or you can have multiple FOREIGN KEY constraints on the same column(s) referencing one PRIMARY KEY of a (different) table each.
Can a table have multiple primary keys justify your answer?
You cannot have multiple primary keys in a table. The reason is that only one field can be used as a unique identification feature for every record.
Can a table have 2 primary keys?
A primary key is a field or set of fields with values that are unique throughout a table. Values of the key can be used to refer to entire records, because each record has a different value for the key. Each table can only have one primary key.
Can there be two primary keys?
No. You cannot use more than 1 primary key in the table. for that you have composite key which is combination of multiple fields.
Can a table contain multiple foreign keys?
A table may have multiple foreign keys, and each foreign key can have a different parent table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys.
Can a table have multiple unique keys?
A table can have more than one unique key unlike primary key. Unique key constraints can accept only one NULL value for column. Unique constraints are also referenced by the foreign key of another table.
Should Join tables have primary keys?
A table must have exactly one primary key to qualify as relational, but that key can be composed of multiple columns. A foreign key, by contrast, is one or more fields or columns that corresponds to the primary key of another table. Foreign keys are what make it possible to join tables to each other.
How many primary keys can a table have Mcq?
A table can have only one primary key. Also, we can create a date variable as a primary key in a table. Unique key also determines each row of the table uniquely, but it can take null value into.
Can a table have no primary key?
Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.
Can we join two tables without primary key?
Yes, you can! The longer answer is yes, there are a few ways to combine two tables without a common column, including CROSS JOIN (Cartesian product) and UNION. The latter is technically not a join but can be handy for merging tables in SQL.
Can a table have both primary key and composite key?
12 Answers. A Table can have a Composite Primary Key which is a primary key made from two or more columns. For example: CREATE TABLE userdata ( userid INT, userdataid INT, info char(200), primary key (userid, userdataid) );