SQL Logical Operators

There are three Logical Operators namely, AND, OR, and NOT. These operators compare two conditions at a time to determine whether a row can be selected for the output. When retrieving data using a SELECT statement, you can use logical operators in the WHERE clause, which allows you to combine more than one condition.

Logical Operators
Description

OR
For the row to be selected at least one of the conditions must be true.

And
For a row to be selected all the specified conditions must be true.

Not
For a row to be selected the specified condition must be false.

"OR" Logical Operator:

If you want to select rows that satisfy at least one of the given conditions, you can use the logical operator, OR.

For example: if you want to find the names of students who are studying either Maths or Science, the query would be like,

SELECT first_name, last_name, subject
FROM student_details
WHERE subject = 'Maths' OR subject = 'Science'

The output would be something like,

First Name
-------------
Anajali
Shekar
Rahul
Stephen

Last Name
-------------
Bhagwat
Gowda
Sharma
Fleming

Subject
-------------
Maths
Maths
Science
Science

The following table describes how logical "OR" operator selects a row.

Column1 Satisfied?
Column2 Satisfied?
Row Selected

"AND" Logical Operator:

If you want to select rows that must satisfy all the given conditions, you can use the logical operator, AND.

For Example: To find the names of the students between the age 10 to 15 years, the query would be like:

SELECT first_name, last_name, age
FROM student_details
WHERE age >= 10 AND age <= 15;

The output would be something like,

First Name
-------------
Anajali
Shekar
Rahul

Last Name
-------------
Bhagwat
Gowda
Sharma

Age
------
12
15
10

The following table describes how logical "AND" operator selects a row.

Column1 Satisfied?
Column2 Satisfied?
Row Selected

"NOT" Logical Operator:

If you want to find rows that do not satisfy a condition, you can use the logical operator, NOT. NOT results in the reverse of a condition. That is, if a condition is satisfied, then the row is not returned.

For example: If you want to find out the names of the students who do not play football, the query would be like:

SELECT first_name, last_name, games
FROM student_details
WHERE NOT games = 'Football'

The output would be something like,

First Name
-------------
Rahul
Stephen
Shekhar
Priya

Last Name
-------------
Sharma
Fleming
Gowde
Chander

Games
------
Cricket
Cricket
Badminton
Chess

The following table describes how logical "NOT" operator selects a row.

Column1 Satisfied?
NOT column1 Satisfied?
Row Selected

Nested Logical Operators:

You can use multiple logical operators in an SQL statement. When you combine the logical operators in a SELECT statement, the order in which the statement is processed is

1) NOT
2) AND
3) OR

For example: If you want to select the names of the students who age is between 10 and 15 years, or those who do not play football, the

SELECT statement would be
SELECT first_name, last_name, age, games
FROM student_details
WHERE age >= 10 AND age <= 15
OR NOT games = 'Football'

The output would be something like,

First Name
-------------
Rahul
Priya

Last Name
-------------
Sharma
Chander

Age
-------------
10
15

Games
------
Cricket
Chess

Condition 1: All the students you do not play football are selected.
Condition 2: All the students whose are aged between 10 and 15 are selected.
Condition 3: Finally the result is, the rows which satisfy atleast one of the above conditions is returned.

NOTE:The order in which you phrase the condition is important, if the order changes you are likely to get a different result.

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