Informatics Practices
Assertion. The PRIMARY KEY can be defined only once in the CREATE TABLE command.
Reason. If the PRIMARY KEY is a composite key, then it is not defined with the individual columns but at the end of the table definition as a table constraint.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
Both A and R are true and R is the correct explanation of A.
Explanation
In SQL, when we define a table using the CREATE TABLE command, we can only specify one PRIMARY KEY constraint. This PRIMARY KEY can consist of a single column or multiple columns (composite key). When a PRIMARY KEY is a composite key (consisting of multiple columns), it's not defined with each individual column but rather as a table constraint at the end of the table definition.
Related Questions
Assertion. In terms of values allowed in a column, both UNIQUE and PRIMARY KEY constraints are not the same.
Reason. UNIQUE allows NULL value once in the column, but PRIMARY KEY does not.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion. The INSERT INTO statement can skip some columns' values.
Reason. Only the columns allowing the NULL values or have default-value-defined, can be skipped in INSERT INTO statement of SQL.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion. INSERT, UPDATE, DELETE, SELECT are the DML commands.
Reason. The DML commands manipulate the data stored in the database tables.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion. The PRIMARY KEY and FOREIGN KEY constraints are similar.
Reason. The FOREIGN KEY constraint links a column of a table with the PRIMARY KEY constraint of another table.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.