EDUCBA

EDUCBA

MENUMENU
  • Free Tutorials
  • Free Courses
  • Certification Courses
  • 360+ Courses All in One Bundle
  • Login

SQL UNION

Home » Data Science » Data Science Tutorials » SQL Tutorial » SQL UNION

SQL UNION

Introduction to SQL UNION

UNION operator in standard query language (SQL) is used to combine result sets obtained from two or more SELECT statements into a single result set. While combining the results of these queries, UNION operator removes all the duplicate values from the final result set. Another popular operator similar to this operator is UNION ALL which is also used to combine the results obtained from two or more SELECT queries but unlike UNION operator, it keeps all the duplicate records in the final result set.

While using UNION operator, we should adhere to following points:

Start Your Free Data Science Course

Hadoop, Data Science, Statistics & others

  • The number of columns being fetched from multiple SELECT queries on which UNION or UNION ALL operator has to be applied must be the same.

Example:

Code:

SELECT name FROM table1
UNION
SELECT name FROM table2;

  • The columns that have to be selected should have the same data type.
  • The sequence of the columns appearing in the SELECT statements must be the same.

Let us have a look at the pictorial depiction of UNION operator and its comparison with UNION ALL.

comparison with UNION ALL.

Syntax and parameters of SQL UNION

The basic syntax for writing SELECT queries with UNION operators is as follows:

SELECT column_name
FROM table_name_1
UNION
SELECT column_name
FROM table_name_2
UNION
SELECT column_name
FROM table_name_3
.
.
.
UNION
SELECT column_name
FROM table_name_n

The parameters used in this syntax are as follows:

  • column_name: column_name corresponds to the name of the column on which we want to use the UNION operator and want to fetch it for the final result set.
  • FROM table_name_1: table_name_1 is the name of the first table from which the records have to be fetched.
  • FROM table_name_2: table_name_2 is the name of the second table from which the records have to be fetched. Same is the case with table_name_3, …, table_name_n.

Of the above mentioned arguments, all of them are mandatory. However, you may use WHERE, , ORDER BY, GROUP BY and HAVING clauses to this syntax based on your requirements.

Examples of SQL UNION

Given below are the examples of SQL UNION:

Let us create two dummy tables called “borrowed_books” and “returned_books”. These tables contain details of books borrowed and returned to a library on a daily basis. We can use the following CREATE statements to create the said tables.

Creating borrowed_books table.

Code:

CREATE TABLE borrowed_books (
book_id INT NOT NULL PRIMARY KEY,
title VARCHAR(100)  NOT NULL,
author_name  VARCHAR(100),
genre VARCHAR(100),
updated_at DATE,
fee_status VARCHAR(100)
);

Creating returned_books table.

Code:

CREATE TABLE returned_books (
book_id INT NOT NULL PRIMARY KEY,
title VARCHAR(100)  NOT NULL,
author_name  VARCHAR(100),
genre VARCHAR(100),
updated_at DATE,
fee_status VARCHAR(100)
);

Let us insert a few records in them to work with using the following INSERT statements.

Popular Course in this category
SQL Training Program (7 Courses, 8+ Projects)7 Online Courses | 8 Hands-on Projects | 73+ Hours | Verifiable Certificate of Completion | Lifetime Access
4.5 (5,230 ratings)
Course Price

View Course

Related Courses
JDBC Training (6 Courses, 7+ Projects)PHP Training (5 Courses, 3 Project)Windows 10 Training (4 Courses, 4+ Projects)PL SQL Training (4 Courses, 2+ Projects)Oracle Training (14 Courses, 8+ Projects)

Code:

INSERT INTO public.borrowed_books(
book_id, title, author_name, genre, updated_at, fee_status)
VALUES
(1, 'The Choice','Edith Eva Eger','Memoir','2020-06-06','Paid'),
(2,'Deep Work','Carl Newport','Self Help','2020-06-16', 'Pending'),
(3, 'A Man Called Ove','Fredrik Backman','Fiction','2020-06-18','Pending'),
(4,'When Breath Becomes Air','Paul Kalanithi','Memoir','2020-06-01','Paid'),
(5,'Man Search for Meaning','Viktor Frankl','Memoir','2020-06-18', 'Pending'),
(6,'The Third Pillar','Raghuram Rajan','Economics','2020-06-11', 'Paid');
select * from borrowed_books;

Output:

SQL UNION 1

Code:

INSERT INTO public.returned_books(
book_id, title, author_name, genre, updated_at, fee_status)
VALUES
(1,'The Choice','Edith Eva Eger','Memoir','2020-06-16','Paid'),
(2,'The Third Pillar','Raghuram Rajan','Economics','2020-06-11', 'Paid'),
(3,'Data Structure & Algorithms','Thomas H. Cormen','Academic','2020-06-18','Paid'),
(4,'When Breath Becomes Air','Paul Kalanithi','Memoir','2020-06-21','Paid'),
(5,'Godaan','Premchand','Fiction','2020-06-15', 'Pending'),
(6,'Deep Work','Carl Newport','Self Help','2020-06-16', 'Pending');
select * from returned_books;

Output:

SQL UNION 2

Example #1

Find the names of all the books available in the library.

Code:

SELECT title
FROM borrowed_books
UNION
SELECT title
FROM returned_books;

Output:

all the books available in the library

In this example, we can observe that all the books have been fetched only once. The duplicate records have been discarded. Let us compare this query with the next query that uses UNION ALL instead of UNION operator.

Code:

SELECT title
FROM borrowed_books
UNION ALL
SELECT title
FROM returned_books;

Output:

SQL UNION 4

What do we observe? We observe that UNION ALL operator fetches all records and does not discard the duplicate ones unlike UNION operator.

Example #2

Find the names of all the books along with their authors and current fee status in the library database.

Code:

SELECT title, author_name, fee_status
FROM borrowed_books
UNION
SELECT title, author_name, fee_status
FROM returned_books;

Output:

long with their authors and current fee status in the library database

Example #3

Find the names of all the books along with their id, authors and current fee status in the library database, for which the library fee is still pending.

Code:

SELECT book_id, title, author_name, fee_status
FROM borrowed_books
WHERE fee_status = 'Pending'
UNION
SELECT book_id, title, author_name, fee_status
FROM returned_books
WHERE fee_status = 'Pending';

Output:

Find the names of all the books

Conclusion

UNION operator in SQL is used to combine results from two or more tables. When combining results from two tables, UNION operator keeps only unique values in the final result set.

Recommended Articles

This is a guide to SQL UNION. Here we discuss the introduction to SQL UNION along with appropriate syntax, parameters and query examples. You may also have a look at the following articles to learn more –

  1. Natural Join in MySQL
  2. Alternate Key in SQL
  3. EXPLAIN in SQL
  4. SQL Minus

SQL Training Program (7 Courses, 8+ Projects)

7 Online Courses

8 Hands-on Projects

73+ Hours

Verifiable Certificate of Completion

Lifetime Access

Learn More

0 Shares
Share
Tweet
Share
Primary Sidebar
SQL Tutorial
  • Functions
    • SQL Date Function
    • SQL String Functions
    • SQL Compare String
    • SQL Window Functions
    • SQL Timestamp
    • SQL TO_DATE()
    • SQL DATEADD()
    • ANY in SQL
    • LIKE Query in SQL
    • BETWEEN in SQL
    • LTRIM() in SQL
    • TOP in SQL
    • SQL Select Top
    • Merge SQL
    • SQL TRUNCATE()
    • SQL UNION
    • SQL ALL
    • SQL INTERSECT
    • SQL Alias
    • SQL Server Substring
    • CUBE in SQL
    • SQL RANK()
    • SQL CTE
    • SQL LAG()
    • SQL MID
    • SQL avg()
    • SQL WEEK
    • SQL DELETE
    • SQL DATEPART()
    • SQL DECODE()
    • SQL DENSE_RANK()
    • SQL NTILE()
    • SQL NULLIF()
    • SQL Stuff
    • SQL Ceiling
    • SQL EXISTS
    • SQL LEAD()
    • SQL ROW_NUMBER
    • SQL Server Replace
    • T-SQL INSERT
    • SQL Ranking Function
  • Basic
    • What is SQL
    • Careers in SQL
    • Careers in SQL Server
    • IS SQL Microsoft?
    • SQL Management Tools
    • What is SQL Developer
    • Uses of SQL
    • How to Install SQL Server
    • What is SQL Server
    • Database in SQL
    • SQL Data Types
    • SQL Keywords
    • Composite Key in SQL
    • SQL Constraints
    • Transactions in SQL
    • First Normal Form
    • SQL Server Data Types
    • SQL Administration
    • SQL Variables
    • Cheat sheet SQL
  • Operators
    • SQL Operators
    • SQL Arithmetic Operators
    • SQL Logical Operators
    • SQL String Operators
    • Ternary Operator in SQL
  • Commands
    • SQL Commands
    • SQL Alter Command
    • SQL Commands Update
    • SQL DML Commands
    • FETCH in SQL
  • Clause
    • SQL Clauses
    • SQL IN Operator
    • SQL LIKE Clause
    • SQL NOT Operator
    • SQL Minus
    • SQL WHERE Clause
    • SQL with Clause
    • SQL HAVING Clause
    • GROUP BY clause in SQL
    • ORDER BY Clause in SQL
    • SQL ORDER BY CASE
    • SQL ORDER BY DATE
    • SQL ORDER BY Alphabetical
    • SQL ORDER BY Ascending
    • SQL GROUP BY Month
    • SQL GROUP BY Multiple Columns
    • SQL GROUP BY DAY
    • SQL GROUPING SETS
  • Queries
    • SQL Insert Query
    • SQL SELECT Query
    • SQL SELECT RANDOM
    • SQL Except Select
    • SQL Subquery
    • SQL SELECT DISTINCT
    • SQL WITH AS Statement
  • Keys
    • SQL Keys
    • Primary Key in SQL
    • Foreign Key in SQL
    • Unique Key in SQL
    • Alternate Key in SQL
  • Joins
    • Join Query in SQL
    • Types of Joins in SQL
    • Types of Joins in SQL Server
    • SQL Inner Join
    • SQL Join Two Tables
    • SQL Delete Join
    • SQL Left Join
    • SQL Right Join
    • SQL Cross Join
    • SQL Outer Join
    • SQL Full Join
    • SQL Self Join
    • Natural Join SQL
    • SQL Multiple Join
  • Advanced
    • Aggregate Functions in SQL
    • IF ELSE Statement in SQL
    • SQL CASE Statement
    • SQL While Loop
    • SQL INSTR()
    • What is Procedure in SQL
    • Stored Procedure in SQL?
    • SQL Server Constraints
    • SQL DELETE ROW
    • Column in SQL
    • Table in SQL
    • SQL Virtual Table
    • SQL Merge Two Tables
    • SQL Table Partitioning
    • SQL Temporary Table
    • SQL Clone Table
    • SQL Rename Table
    • SQL LOCK TABLE
    • SQL Mapping
    • Cursors in SQL
    • AND in SQL
    • Wildcard in SQL
    • SQL FETCH NEXT
    • SQL Views
    • Triggers in SQL
    • SQL UPDATE Trigger
    • SQL AFTER UPDATE Trigger
    • SQL Update Statement
    • SQL DROP TRIGGER
    • Views in MySQL
    • SQL COMMIT
    • Distinct Keyword in SQL
    • PARTITION BY in SQL
    • SQL Set Operators
    • SQL UNION ALL
    • Metadata in SQL
    • SQL Bulk Insert
    • Array in SQL
    • SQL REGEXP
    • JSON in SQL
    • SQL For loop
    • EXPLAIN in SQL
    • SQL Cluster
    • SQL Backup
    • SQL Pattern Matching
    • SQL Users
    • ISNULL SQL Server
    • SQL Import CSV
  • Interview Questions
    • SQL Interview Questions
    • Advance SQL Interview Questions
    • SQL Joins Interview Questions
    • SQL Server Interview Questions

Related Courses

JDBC Training Course

PHP course

Windows 10 Training

SQL Course Training

PL/SQL Certification Courses

Oracle Certification Courses

Footer
About Us
  • Blog
  • Who is EDUCBA?
  • Sign Up
  • Corporate Training
  • Certificate from Top Institutions
  • Contact Us
  • Verifiable Certificate
  • Reviews
  • Terms and Conditions
  • Privacy Policy
  •  
Apps
  • iPhone & iPad
  • Android
Resources
  • Free Courses
  • Database Management
  • Machine Learning
  • All Tutorials
Certification Courses
  • All Courses
  • Data Science Course - All in One Bundle
  • Machine Learning Course
  • Hadoop Certification Training
  • Cloud Computing Training Course
  • R Programming Course
  • AWS Training Course
  • SAS Training Course

© 2020 - EDUCBA. ALL RIGHTS RESERVED. THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS.

EDUCBA
Free Data Science Course

Hadoop, Data Science, Statistics & others

*Please provide your correct email id. Login details for this Free course will be emailed to you
Book Your One Instructor : One Learner Free Class

Let’s Get Started

This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to our Privacy Policy

EDUCBA

*Please provide your correct email id. Login details for this Free course will be emailed to you
EDUCBA Login

Forgot Password?

EDUCBA
Free Data Science Course

Hadoop, Data Science, Statistics & others

*Please provide your correct email id. Login details for this Free course will be emailed to you

Special Offer - SQL Training Program (7 Courses, 8+ Projects) Learn More