SQL EXCLUDE

Introduction to SQL EXCLUDE

In SQL, in order to EXCLUDE certain rows from being returned by a SELECT query, we use some restricting or excluding conditions based on some criteria. EXCLUDE conditions in SQL usually appear in the WHERE clause of the statement or in the HAVING clause of an aggregate query. Some commonly used EXCLUDE operators in SQL are NOT, NOT IN, NOT LIKE, ‘!=’, EXCEPT, NOT NULL, etc.

You must be wondering what happens when you mention a restricting condition in a SELECT statement. It is actually pretty simple. When the SELECT query runs, the database server applies the restricting condition on each row that is being fetched while searching. If the row meets the mentioned condition, it is included.

Syntax and Parameters

The basic syntax for writing exclude queries in SQL are as follows:

SELECT column_name1, column_name2, ...
FROM table_name
WHERE column_name1 conditional_operator comparision_expression;

If you want to write exclude queries using the EXCEPT operator, the syntax is as follows :

SELECT column_name1, column_name2, ...
FROM table_name1
EXCEPT
SELECT column_name1, column_name2, ...
FROM table_name2;

Parameters:

The parameters used in the above-mentioned syntax are as follows :

• column_name1, column_name2, … : columns or field names that have to be fetched for the final result set.
• table_name1, table_name2: database tables from which the above-mentioned columns have to be fetched.
• conditonal_operator: operators such as (NOT IN, NOT LIKE, NOT NULL, NOT EQUAL TO (!=), etc.)
• comparison_expression: subquery or expression based on which exclusion has to be done.

Examples of SQL EXCLUDE

In order to illustrate the excluding or restricting of certain rows in SQL, let us create a dummy table called “students”. We can use the following CREATE statement to create the student’s table.

CREATE TABLE students(
roll_no int NOT NULL PRIMARY KEY,
student_name VARCHAR(255),
degree_major VARCHAR(255) NOT NULL,
degree_year VARCHAR(255),
society VARCHAR(255)
);

Having created the students table. Let us insert a few records in it to work with.

INSERT INTO [practice_db].[dbo].[students] ([roll_no] ,[student_name] ,[degree_major] ,[degree_year] ,[society])
VALUES
(1,'Mohith K','Computer Science Engineering','IV','Dramatics'),
(2,'Ayesha Khan','Electrical Engineering','I','Music'),
(3,'Kylie Green','Computer Science Engineering','III','Choreography'),
(4,'Alisha Rojer','Chemical Engineering','III','Music'),
(5,'Andy Bernard','Geosciences','IV','Dramatics')
GO

The data in the students table looks something as follows:

Now we are all set to try some examples on excluding rows in SQL.

Example #1

Exclude rows using NOT EQUAL to operator

Find details of all the students excluding students with roll_no 4.

SELECT *
FROM students
WHERE roll_no != 4 ;

 

Example #2

Exclude rows using NOT LIKE operator

Find details of all the students excluding student whose name starts with A.

SELECT *
FROM students
WHERE student_name NOT LIKE 'A%';

Example #3

Exclude rows using NOT IN operator

Find details of all the students excluding students whose roll_no is not 1, 3, or 5.

SELECT *
FROM students
WHERE roll_no NOT IN (1,3,5);

Example #4

Exclude rows using NOT  IN operator with subqueries on the same table.

Find details of all the students excluding student who are from ‘Dramatics’ or ‘Music’ society.

SELECT *
FROM students
WHERE student_name NOT IN (SELECT student_name
FROM students
WHERE
society = 'Dramatics' OR society = 'Music' );

Exclude rows using NOT IN operator with subqueries on a different table.

In order to illustrate this, let us create a table called “home_town” that contains details pertaining to the home cities of students in the students table.

CREATE TABLE [dbo].[home_town](
[roll_no] [int] NOT NULL,
[home_city] [varchar](50) NULL
)
INSERT INTO [practice_db].[dbo].[home_town] ([roll_no] ,[home_city])
VALUES
(2, 'New York'),
(3, 'New Jersey'),
(5, 'Denver')
GO

Example #5

Find details of all the students excluding student whose roll_no is not in the list of roll_nos where the home_city is ‘Denver’.

SELECT *
FROM students
WHERE roll_no <> (SELECT roll_no
FROM home_town
WHERE home_city = 'Denver' );

Example #6

Exclude rows with NULL values from a LEFT / RIGHT JOIN

Find the roll_no, student_name, degree_major, society, and home_city for students excluding rows where home_city is NULL or does not exist.

SELECT s.roll_no,
s.student_name,
s.degree_major,
s.degree_year,
s.society,
h.home_city
FROM students as s LEFT JOIN home_town as h
ON s.roll_no = h.roll_no
WHERE h.roll_no IS NOT NULL;

Example #7

Exclude rows using EXCEPT operator

In order to exclude rows that are present only in the results of the first select statement but not in the second, we can use EXCEPT operator.

Find the roll_no of all the students except those mentioned in the home_town table.

SELECT roll_no
FROM students
EXCEPT
SELECT roll_no
FROM home_town;

Advantages

Some of the advantages are given below:

1. Helps in limiting the number and kind of rows that can make it to the final result set.
2. Helps to extract and insert only relevant results when using SQL queries, such as: SELECT, UPDATE, or DELETE statement.

Conclusion

To restrict the kind and number of rows a SELECT query should return, we use some exclude conditions which work as filter criteria. These filter criteria are mentioned in the WHERE clause of SELECT, UPDATE or DELETE statements.

Recommend ed Articles

This is a guide to SQL EXCLUDE. Here we also discuss the introduction and syntax and parameters of sql exclude along with different examples and its code implementation. You may also have a look at the following articles to learn more –

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