What happens to foreign key when primary key is updated?
No the foreign key is not updated automatically. You need to update the foreign key in the tables in which it is referenced by yourself else it would result in referential integrity exception. For updating the foreign key automatically you may use TRIGGERS.
When primary key constraint is applied to one or more columns then it is known as?
Answer: Option:3) composite primary key.
What are two constraints added with primary key?
If a primary key consists of multiple columns, it has to be defined at the end of the CREATE TABLE statement. There is a restriction on the data type of the primary key column e.g., it cannot be BLOB , CLOB , ARRAY or NCLOB .
How to set existing column as primary key?
To set existing column as primary key, run following sql script in the Query window. Note the value in table for UserID should not be duplicate one. Here you are getting error because the value in UserId is more than once that value is 5. Thanks for contributing an answer to Stack Overflow!
Do you have to declare primary key in ALTER TABLE?
Note: If you use ALTER TABLE to add a primary key, the primary key column (s) must have been declared to not contain NULL values (when the table was first created).
How to create a primary key in SQL?
The following SQL creates a PRIMARY KEY on the “ID” column when the “Persons” table is created: To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax: Note: In the example above there is only ONE PRIMARY KEY (PK_Person).
Can a primary key constraint be defined on more than one column?
If a primary key constraint is defined on more than one column, values may be duplicated within one column, but each combination of values from all the columns in the primary key constraint definition must be unique.