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.
SQL Queries
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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.
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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.