Comparison operators in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all rows where age is equal to 30.

MySQL

SELECT * FROM users WHERE age [1] 30;

Drag options to blanks, or click blank then click option'

A>

B!=

C=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '=' will select rows where age is not 30.

Using '>' or '<' will select rows with age greater or less than 30, not equal.

The equal sign = is used to compare if two values are the same.

2fill in blank

medium

Complete the code to select all rows where salary is greater than 50000.

MySQL

SELECT * FROM employees WHERE salary [1] 50000;

Drag options to blanks, or click blank then click option'

A>

B<=

C=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' will select salaries less than or equal to 50000.

Using '=' will select only salaries exactly 50000.

The greater than operator > selects values larger than the given number.

3fill in blank

hard

Fix the error in the code to select rows where score is not equal to 100.

MySQL

SELECT * FROM results WHERE score [1] 100;

Drag options to blanks, or click blank then click option'

A<>

B!=

C==

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using == causes syntax errors in SQL.

Using = selects rows equal to 100, not different.

In MySQL, the not equal operator can be written as <> or !=. Both are valid, but <> is often preferred for compatibility.

4fill in blank

hard

Fill both blanks to select rows where price is between 10 and 20 (inclusive).

MySQL

SELECT * FROM products WHERE price [1] 10 AND price [2] 20;

Drag options to blanks, or click blank then click option'

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or < excludes the boundary values.

Mixing up the operators will select wrong price ranges.

To select prices between 10 and 20 including both, use >= for the lower bound and <= for the upper bound.

5fill in blank

hard

Fill all three blanks to select rows where quantity is greater than 5, less than 15, and not equal to 10.

MySQL

SELECT * FROM inventory WHERE quantity [1] 5 AND quantity [2] 15 AND quantity [3] 10;

Drag options to blanks, or click blank then click option'

A>

B<

C!=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using = instead of != will select quantity equal to 10.

Using wrong comparison operators will select incorrect rows.

This query selects quantities greater than 5, less than 15, and not equal to 10 using >, <, and != operators respectively.

Practice

1. Which of the following comparison operators in MySQL means "not equal to"?

easy

A. =

B. <>

C. >=

D. <

Solution

1. Step 1: Understand the meaning of comparison operators

   The operator "<>" is used in SQL to mean "not equal to".

2. Step 2: Compare with other operators

   "=" means equal, ">=" means greater than or equal, and "<" means less than.

3. Final Answer:

   <> -> Option B

4. Quick Check:

   Not equal operator = <> [OK]

Hint: Remember: <> means not equal in SQL [OK]

Common Mistakes:

• Confusing = with not equal
• Using != which is valid but less common in MySQL
• Mixing up > and < operators

2. Which of the following is the correct syntax to check if column age is greater than 18 in a WHERE clause?

easy

A. WHERE age > 18

B. WHERE age => 18

C. WHERE age =< 18

D. WHERE age <> 18

Solution

1. Step 1: Identify the correct greater than operator

   The correct operator for "greater than" is ">". The operator ">=" means "greater than or equal to".

2. Step 2: Check syntax correctness

   "=>" and "=<" are invalid operators in SQL syntax. "<>" means not equal, which is not what we want.

3. Final Answer:

   WHERE age > 18 -> Option A

4. Quick Check:

   Greater than operator is > [OK]

Hint: Use > for greater than, not => or =< [OK]

Common Mistakes:

• Using => or =< which are invalid
• Confusing <> with greater than
• Using = instead of >

3. Given the table Employees with a column salary, what will the query SELECT * FROM Employees WHERE salary <= 50000; return?

medium

A. All employees with salary less than or equal to 50000

B. All employees with salary exactly 50000

C. All employees with salary less than 50000

D. All employees with salary greater than 50000

Solution

1. Step 1: Understand the meaning of <= operator

   The operator <= means "less than or equal to".

2. Step 2: Interpret the query condition

   The query filters employees whose salary is either less than 50000 or exactly 50000.

3. Final Answer:

   All employees with salary less than or equal to 50000 -> Option A

4. Quick Check:

   <= means less than or equal [OK]

Hint: <= means less than or equal, includes the number [OK]

Common Mistakes:

• Thinking <= means only less than
• Confusing <= with <
• Ignoring the equal part of <= operator

4. Identify the error in this MySQL query: SELECT * FROM Products WHERE price ! 100;

medium

A. Missing comparison operator after !

B. No error, query is correct

C. Missing quotes around 100

D. Incorrect use of ! for not equal, should be != or <>

Solution

1. Step 1: Analyze the use of ! operator

   In MySQL, "!" alone is not a valid comparison operator. For "not equal", use "!=" or "<>".

2. Step 2: Check the query syntax

   The query uses "price ! 100" which is invalid syntax and will cause an error.

3. Final Answer:

   Incorrect use of ! for not equal, should be != or <> -> Option D

4. Quick Check:

   Use != or <> for not equal [OK]

Hint: Use != or <> for not equal, not just ! [OK]

Common Mistakes:

• Using ! alone as not equal
• Forgetting to use != or <>
• Assuming ! means not equal in SQL

5. You want to select all customers whose age is between 20 and 30 inclusive. Which WHERE clause correctly uses comparison operators?

hard

A. WHERE age > 20 AND age < 30

B. WHERE age = 20 OR age = 30

C. WHERE age >= 20 AND age <= 30

D. WHERE age <> 20 AND age <> 30

Solution

1. Step 1: Understand the requirement for inclusive range

   Inclusive means including 20 and 30, so use >= and <= operators.

2. Step 2: Analyze each option

   WHERE age > 20 AND age < 30 excludes 20 and 30 (strictly greater and less). WHERE age = 20 OR age = 30 only selects exactly 20 or 30, not the range. WHERE age <> 20 AND age <> 30 excludes 20 and 30, opposite of requirement.

3. Final Answer:

   WHERE age >= 20 AND age <= 30 -> Option C

4. Quick Check:

   Use >= and <= for inclusive ranges [OK]

Hint: Use >= and <= for inclusive range checks [OK]

Common Mistakes:

• Using > and < excludes boundary values
• Using OR instead of AND for range
• Using <> which excludes values