Informatics Practices
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.
Answer
Both A and R are true and R is the correct explanation of A.
Explanation
The UNIQUE and PRIMARY KEY constraints are similar in that they both ensure uniqueness of values in a column or set of columns. However, they differ in terms of the values they allow, particularly regarding NULL values. UNIQUE allows NULL values, whereas PRIMARY KEY does not.
Related Questions
The keyword BETWEEN can be used in a WHERE clause to refer to a range of values.
Assertion. The UNIQUE and PRIMARY KEY constraints are similar but not the same.
Reason. There can be only one column with PRIMARY KEY constraint, in a 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.
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. 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.