Informatics Practices
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.
Answer
Both A and R are true but R is not the correct explanation of A.
Explanation
Both the UNIQUE and PRIMARY KEY constraints ensure unique values for each row in a column. However, UNIQUE allows NULL values, whereas PRIMARY KEY does not. There can exist multiple columns with UNIQUE constraints in a table, but only one column can have a PRIMARY KEY constraint.
Related Questions
The keyword LIKE can be used in a WHERE clause to refer to a range of values.
The keyword BETWEEN can be used in a WHERE clause to refer to a range of values.
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.