SQL DML - 50 MCQs

Flashcards for SQL DML MCQs

SELECT

Retrieve data

What clause must follow the SELECT clause?

FROM

SELECT * FROM employees;

Selects all columns

DISTINCT keyword

Returns only unique values

Which keyword assigns an alias to a column?

AS

Which keyword is optional but recommended when using aliases?

AS

Which clause restricts the rows returned in a query?

WHERE

Which comparison operator means 'not equal'?

<> and !=

WHERE first_name LIKE 'S%'

First names that start with 'S'

Which character is used in LIKE to represent a single character?

_

What does IN check for?

A value in a list

What will IS NULL return?

All rows with NULL in the column

Which operator checks if a value lies within a specific range?

BETWEEN

Which of the following is a valid logical operator?

NOT, OR, AND

What is the result of AND if both conditions are TRUE?

TRUE

What does NOT do?

Reverses the condition

What is the first order of precedence in SQL evaluation?

Comparison operators

How can you override precedence in SQL?

Use parentheses

What is the default order for ORDER BY?

Ascending

Which clause is used to sort rows in SQL?

ORDER BY

Which symbol is used for multiplication in SQL?

*

Which has higher precedence: addition or multiplication?

Multiplication

Which operator is used to concatenate strings?

||

Which query shows full employee name and department number?

SELECT firstname || ' ' || lastname || ' works in department ' || department_id FROM employees;

SELECT table1.column1, table2.column2 FROM table1, table2 WHERE table1.id = table2.id;

Joins two tables

What is a table alias?

A temporary table name

Which JOIN returns only matched records from both tables?

INNER JOIN

Which JOIN returns all records from the left table?

LEFT JOIN

Which JOIN gives a Cartesian product?

CROSS JOIN

What is the result of FULL OUTER JOIN?

All matched and unmatched rows

Which statement adds new rows?

INSERT

What happens if you insert a row with a foreign key that doesn't exist?

Error

What is the correct syntax for inserting values?

INSERT INTO table (columns) VALUES (values);

What clause is optional in UPDATE but critical to target specific rows?

WHERE

What happens if you omit WHERE in UPDATE?

All rows updated

How do you delete all rows from a table?

DELETE FROM table;

What command can undo a DELETE (if not committed)?

ROLLBACK

What happens when a DELETE has no WHERE clause?

All rows deleted

What must you do before inserting a new department with a new location?

Insert into locations table first

How do you correct a wrongly inserted department name?

UPDATE

What does a SELF JOIN do?

Joins a table to itself

What does the CROSS JOIN result in?

Cartesian product

Which join displays customers even if they haven't placed orders?

LEFT JOIN

What is the purpose of using AS in a JOIN?

Assign aliases

SELECT A.name, B.name FROM A, B WHERE A.city = B.city, what type of join is this?

Equi-Join

Which command saves all changes made in a session?

COMMIT

What is needed to avoid invalid foreign key entries?

Existing referenced records

SELECT * FROM employees WHERE salary BETWEEN 3000 AND 6000;

Shows salaries from 3000 to 6000

What type of JOIN will always show nulls for unmatched rows on both sides?

FULL OUTER

What command permanently removes a table?

DROP