DbSchema Tutorial| SQL AND,OR,NOT OPERATORS

SQL Tutorial • 22-Jul-2023

by Malik Umair Sajjad

Structured Query Language (SQL) is an essential tool for individuals working with databases. One of SQL’s most potent features is its ability to filter and sort data using specific criteria. This tutorial will dive deep into the AND, OR, and NOT operators, explaining their roles in data filtering with detailed examples.

Introduction to SQL Filtering

SQL allows us to extract specific datasets from databases. The core strength lies in its filtering capabilities, enabling users to sift through vast tables and pull out only the relevant information. This precision is achieved using conditional operators like AND, OR, and NOT.

Sample Database Table

For our tutorial, let’s work with a fictional Students table. The table schema is as follows:

StudentID (INTEGER): A unique identifier for each student.
FirstName (TEXT): The first name of the student.
Age (INTEGER): Age of the student.
Grade (TEXT): The grade obtained by the student.

Sample data from the table:

StudentID	FirstName	Age	Grade
1	Alice	20	A
2	Bob	22	B
3	Charlie	21	A
4	David	20	C
5	Eve	23	B

AND Operator

The AND operator retrieves records meeting all the specified conditions. For a record to be selected, every condition must be true.

Syntax:

SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2 ...;

Example:

To pinpoint students aged 20 with an A grade:

SELECT * FROM Students
WHERE Age=20 AND Grade='A';

Result:

StudentID	FirstName	Age	Grade
1	Alice	20	A

Explanation:

Alice is the sole student aged 20 with a grade ‘A’.

OR Operator

The OR operator is less strict, returning records if any one of the conditions is true.

Syntax:

SELECT column1, column2, ...
FROM table_name
WHERE condition1 OR condition2 ...;

Example:

To list students either aged 20 or having a grade of A:

SELECT * FROM Students
WHERE Age=20 OR Grade='A';

Result:

StudentID	FirstName	Age	Grade
1	Alice	20	A
3	Charlie	21	A
4	David	20	C

Explanation:

Alice and Charlie both achieved grade ‘A’. Among them, Alice and David are 20 years old.

NOT Operator

NOT inverts a condition’s outcome. If a condition is true, NOT renders it false and vice-versa.

Syntax:

SELECT column1, column2, ...
FROM table_name
WHERE NOT condition;

Example:

To identify students not aged 20:

SELECT * FROM Students
WHERE NOT Age=20;

Result:

StudentID	FirstName	Age	Grade
2	Bob	22	B
3	Charlie	21	A
5	Eve	23	B

Explanation:

Bob, Charlie, and Eve are not 20 years old.

Combining AND, OR, NOT Operators

When using multiple operators, it’s pivotal to use parentheses to ensure the desired order of evaluation.

Syntax:

SELECT column1, column2, ...
FROM table_name
WHERE (condition1 AND condition2) OR (condition3 AND condition4) ...;

Example:

To locate students aged 20 with grade A or those aged 22:

SELECT * FROM Students
WHERE (Age=20 AND Grade='A') OR Age=22;

Result:

StudentID	FirstName	Age	Grade
1	Alice	20	A
2	Bob	22	B

Explanation:

Alice satisfies the first set of conditions, while Bob fulfills the second.

Common Mistakes

Order of Evaluation: Ensure you’re aware that AND is evaluated before OR. Using parentheses can prevent confusion.
String Quotation: Always enclose string values within single quotes.

Frequently Asked Questions

Is there a limit to the number of AND and OR operators in a query?
- Technically, there’s no set limit. However, for clarity, avoid making your conditions overly complex.
How do != and NOT differ?
- != signifies inequality between values. Conversely, NOT negates a condition.

Practice Questions

Identify students aged 21 or 23.
List students without an A grade.
Find students aged 20 not holding an A grade.
Show students graded B or C, but exclude those aged 23.

By mastering these operators, SQL users can harness the full potential of their databases, ensuring that they always obtain the exact data they need. The beauty of SQL lies in its powerful simplicity, and with practice, these commands will become second nature.

Thank you for following along with this tutorial. Keep practicing and stay tuned for more comprehensive SQL tutorials!

Happy coding!

Remember: Practice makes perfect! The more you use these commands in different combinations, the more comfortable you’ll become with the SQL syntax.