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MCQ | SQL – Constraints Clause
SQL Constraints MCQ: This section contains the Multiple-Choice Questions & Answers on SQL Constraints.
Submitted by Anushree Goswami, on October 28, 2021
SQL Constraints Clause MCQs
1. By constraining a SQL statement, we limit the ____ according to certain conditions or restrictions.
- Row
- Column
- Table
- Database
Answer: D) Database
Explanation:
By constraining a SQL statement we limit the database according to certain conditions or restrictions.
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2. Which of the following is/are type of SQL Constraint?
- Column Level
- Table Level
- Both A and B
- None of the above
Answer: C) Both A and B
Explanation:
SQL Constraints can be categorized in two types:
- Column Level Constraint
- Table Level Constraint
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3. What is the difference between Column Level and Table Level Constraints?
- Constraints are applied to a single row using Column Level Constraints whereas Multiple rows can be constrained using a Table Level Constraint.
- Constraints are applied to multiple rows using Column Level Constraints whereas a single row can be constrained using a Table Level Constraint.
- Constraints are applied to a single column using Column Level Constraints whereas Multiple columns can be constrained using a Table Level Constraint.
- Constraints are applied to multiple columns using Column Level Constraints whereas only a single column can be constrained using a Table Level Constraint.
Answer: C) Constraints are applied to a single column using Column Level Constraints whereas Multiple columns can be constrained using a Table Level Constraint
Explanation:
Constraints are applied to a single column using Column Level Constraints whereas Multiple columns can be constrained using a Table Level Constraint.
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4. Which of the following constraints are TRUE to be put in Password system?
- One uppercase character must be included in the password.
- An eight-character minimum password is required.
- At least one symbol must appear in the password.
- All of the above
Answer: D) All of the above
Explanation:
The constraints that are needed to be put in the Password system are:
- One uppercase character must be included in the password.
- An eight-character minimum password is required.
- At least one symbol must appear in the password.
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5. Select the correct constraint in SQL?
- NOT NULL
- CHECK
- DEFAULT
- All of the above
Answer: D) All of the above
Explanation:
The constraints available in SQL are:
- CHECK
- CREATE INDEX
- DEFAULT
- FOREIGN KEY
- NOT NULL
- PRIMARY KEY
- UNIQUE
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6. What is TRUE about NOT NULL Constraint?
- In columns that are subject to the NOT NULL constraint, duplicate values are not allowed.
- When a table's column is declared as NOT NULL, no record in the table can have an empty value for that column.
- By applying the NOT NULL constraint, we will always ensure that the column contains a unique value and won't allow nulls.
- The value will first be checked for certain conditions before inserting it into the column when a NOT NULL constraint applies to a column in the table.
Answer: B) When a table's column is declared as NOT NULL, no record in the table can have an empty value for that column
Explanation:
When a table's column is declared as NOT NULL, no record in the table can have an empty value for that column.
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7. NULL means –
- ZERO
- -1
- 1
- Empty
Answer: D) Empty
Explanation:
NULL means empty, not even zero.
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8. Which of the following is TRUE about UNIQUE constraint?
- In columns that are subject to the UNIQUE constraint, duplicate values are not allowed.
- Unique values will always be present in the column containing the unique constraint.
- A single table can have more than one unique constraint, since it can be applied to more than one column.
- All of the above
Answer: D) All of the above
Explanation:
In case of UNIQUE constraint:
- In columns that are subject to the UNIQUE constraint, duplicate values are not allowed.
- Unique values will always be present in the column containing the unique constraint.
- A single table can have more than one unique constraint, since it can be applied to more than one column.
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9. You can also ____ the existing tables by using the UNIQUE constraint.
- Change
- Delete
- Modify
- Drop
Answer: C) Modify
Explanation:
You can also modify the existing tables by using the UNIQUE constraint.
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10. ____ and ____constraints form the core of the PRIMARY KEY constraint.
- NOT NULL , CHECK
- NOT NULL , DEFAULT
- NOT NULL , FOREIGN KEY
- NOT NULL , UNIQUE
Answer: D) NOT NULL , UNIQUE
Explanation:
NOT NULL and UNIQUE constraints form the core of the PRIMARY KEY constraint.
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11. ____ integrity is achieved by using a foreign key.
- Referential Integrity
- Domain Integrity
- User-defined Integrity
- Entity Integrity
Answer: A) Referential Integrity
Explanation:
Referential integrity is achieved by using a foreign key.
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12. What is TRUE about DEFAULT constraint?
- The value will first be checked for certain conditions before inserting it into the column when a DEFAULT constraint applies to a column in the table.
- In the event of a DEFAULT constraint being applied to a table's column without a user specifying the value to be inserted when that constraint was applied, the default value that was specified when the constraint was applied will be put into that column.
- An index can be created on the table using the DEFAULT constraint.
- None of the above
Answer: B) In the event of a DEFAULT constraint being applied to a table's column without a user specifying the value to be inserted when that constraint was applied, the default value that was specified when the constraint was applied will be put into that column
Explanation:
In the event of a default constraint is applied to a table's column without a user specifying the value to be inserted when that constraint was applied, the default value that was specified when the constraint was applied will be put into that column.
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