PostgreSQL Tutorial: CONCAT Function

June 23, 2024

Summary: in this tutorial, you will learn how to use the PostgreSQL CONCAT() function to concatenate two or more strings into one.

Table of Contents

Introduction to PostgreSQL CONCAT() function

To concatenate two or more strings into a single string, you can use the string concatenation operator || as shown in the following example:

SELECT
   'John' || ' ' || 'Doe' AS full_name;

Output:

 full_name
-----------
 John Doe
(1 row)

The following statement uses the concatenation operator (||) to concatenate a string with NULL:

SELECT
   'John' || NULL result;

It returns NULL.

 result
--------
 null
(1 row)

Since version 9.1, PostgreSQL has introduced a built-in string function called CONCAT() to concatenate two or more strings into one.

Here’s the basic syntax of the CONCAT() function:

CONCAT(string1, string2, ...)

The CONCAT function accepts a list of input strings, which can be any string type including CHAR, VARCHAR, and TEXT.

The CONCAT() function returns a new string that results from concatenating the input strings.

Unlike the concatenation operator ||, the CONCAT function ignores NULL arguments.

To concatenate two or more strings into one using a specified separator, you can use the CONCAT_WS() function.

PostgreSQL CONCAT() function examples

Let’s take some examples of using the PostgreSQL CONCAT() function.

1) Basic PostgreSQL CONCAT() function example

The following example uses the CONCAT() function to concatenate three literal strings into one:

SELECT 
  CONCAT ('John', ' ', 'Doe') full_name;

Output:

 full_name
-----------
 John Doe
(1 row)

2) Using the CONCAT() function with table data example

We’ll use the customer table from the sample database:

customer table

The following statement uses the CONCAT() function to concatenate values in the first_name, a space, and values in the last_name columns of the customer table into a single string:

SELECT 
  CONCAT (first_name, ' ', last_name) AS full_name 
FROM 
  customer 
ORDER BY 
  full_name;

Output:

       full_name
-----------------------
 Aaron Selby
 Adam Gooch
 Adrian Clary
 Agnes Bishop
 Alan Kahn
...

3) Using the CONCAT() function with NULL

First, create a table called contacts and insert some rows into it:

CREATE TABLE contacts (
    id SERIAL PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL,
    phone VARCHAR(15)
);

INSERT INTO contacts (name, email, phone) 
VALUES
    ('John Doe', 'john@gmail.com', '123-456-7890'),
    ('Jane Smith', 'jane@example.com', NULL),
    ('Bob Johnson', 'bob@example.com', '555-1234'),
    ('Alice Brown', 'alice@example.com', NULL),
    ('Charlie Davis', 'charlie@example.com', '987-654-3210')
RETURNING *;

Output:

 id |     name      |        email        |    phone
----+---------------+---------------------+--------------
  1 | John Doe      | john@gmail.com      | 123-456-7890
  2 | Jane Smith    | jane@example.com    | null
  3 | Bob Johnson   | bob@example.com     | 555-1234
  4 | Alice Brown   | alice@example.com   | null
  5 | Charlie Davis | charlie@example.com | 987-654-3210
(5 rows)

INSERT 0 5

Second, use the CONCAT() function to concatenate the values in the name, email, and phone columns of the contacts table:

SELECT
  CONCAT(name, ' ', '(', email, ')', ' ', phone) contact
FROM 
  contacts;

Output:

                     contact
--------------------------------------------------
 John Doe (john@gmail.com) 123-456-7890
 Jane Smith (jane@example.com)
 Bob Johnson (bob@example.com) 555-1234
 Alice Brown (alice@example.com)
 Charlie Davis (charlie@example.com) 987-654-3210
(5 rows)

The output indicates that the CONCAT() function ignores NULL.

Summary

Use the PostgreSQL CONCAT() function to concatenate two or more strings into one.

See more

PostgreSQL Tutorial: String Functions

PostgreSQL Documentation: String Functions and Operators

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