Assertion. The treatment of NULL values is different with PRIMARY KEY and UNIQUE constraints.

Reason. The column(s) with PRIMARY KEY do not allow the NULL value even in a single row but UNIQUE constraint allows NULL for one of the rows.

Assertion. There is no restriction on the number of columns that can have PRIMARY KEY constraint or UNIQUE constraints.

Reason. There can be multiple columns with UNIQUE constraint but PRIMARY KEY constraint can be defined only once for one or more columns.

Assertion. There are different commands for creating and changing table design.

Reason. The CREATE TABLE command creates the tables while ALTER TABLE command changes the design of an existing table.

Assertion. Both DELETE and DROP TABLE carry out the same thing — deletion in tables.

Reason. The DELETE command deletes the rows and DROP TABLE deletes the whole table.

Assertion. Both UPDATE and ALTER TABLE commands are similar.

Reason. The UPDATE command as well ALTER TABLE command make changes in the table.

Assertion. SQL SELECT's GROUP BY clause is used to divide the result in groups.

Reason. The GROUP BY clause combines all those records that have identical values in a particular field or in group by fields.

Assertion. A GROUP BY query can also include functions.

Reason. ALL SQL functions can be used in a GROUP BY query.

Assertion. SQL SELECT query can also fetch rows from multiple tables.

Reason. A join is a query that combines rows from two or more tables.

Assertion. Generally, a join query combines rows from multiple tables having some common column(s) and a joining condition, but not always.

Reason. A Cartesian product is an unrestricted join where all possible combinations of rows from multiple tables are created without any condition on them.

Assertion. The join, in which columns are compared for equality, is called Equi-join.

Reason. The join queries only produce combined rows from tables having some common column, when compared for equality.