MCQ – Basic SQL multiple-choice questions with answers for written test in software job interview in IT companies.
Q) Which statement is wrong about PRIMARY KEY constraint in SQL?
- The PRIMARY KEY uniquely identifies each record in a SQL database table
- Primary key can be made based on multiple columns
- Primary key must be made of any single columns
- Primary keys must contain UNIQUE values.
Q) Which is/are correct statements about primary key of a table?
- Primary keys can contain NULL values
- Primary keys cannot contain NULL values.
- A table can have only one primary key with single or multiple fields
- A table can have multiple primary keys with single or multiple fields
Q) In existing table, ALTER TABLE statement is used to
- Add columns
- Add constraints
- Delete columns
- Delete constrains
- All of the above
Q) SQL Query to delete all rows in a table without deleting the table (structure, attributes, and indexes)
- DELETE FROM table_name;
- DELETE TABLE table_name;
- DROP TABLE table_name;