PostgreSQL

In PostgreSQL, the CONCAT function is a part of Data Query Language (DQL) used to combine two or more strings into a single string. It is especially useful when you need to merge multiple fields or values in a query result, such as combining first names and last names from a customer database. The CONCAT function can accept multiple arguments and will return a single concatenated string. This function ensures that even if one or more values are NULL, the non-NULL values will still be concatenated.

Here's a basic example to illustrate how the CONCAT function works:

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

In this case, the result would be 'John Doe'.

How to Use CONCAT in PostgreSQL (Step by Step)

1. Basic Syntax ofCONCAT:
   • The basic syntax of the CONCAT function is:

     SELECT CONCAT(string1, string2, ..., stringN) AS alias_name;
     
     

   • Example:

     SELECT CONCAT('Account Number: ', 12345) AS account_info;
     
     

     This will return 'Account Number: 12345'.

2. Concatenating Column Values:
   • You can concatenate column values from your database tables. This is useful for merging fields like customer first names and last names.
   • Example:

     SELECT CONCAT(first_name, ' ', last_name) AS full_name
     FROM customers;
     

3. HandlingNULLValues:
   • If any of the arguments to CONCAT is NULL, it still works by ignoring the NULL and concatenating the rest.
   • Example:

     SELECT CONCAT(first_name, ' ', middle_name, ' ', last_name) AS full_name
     FROM customers;
     

     Even if middle_name is NULL, it will still return a valid full_name.

4. UsingCONCATwith Numeric Values:
   • PostgreSQL automatically casts numeric values to strings when using CONCAT. This means you can easily merge strings and numbers
   .
   • Example:

     SELECT CONCAT('Transaction ID: ', transaction_id, ', Amount: $', amount) AS transaction_info
     FROM transactions;
     

5. CombiningCONCATwith Other String Functions:
   • You can combine CONCAT with other string functions like UPPER, LOWER, TRIM, etc., to manipulate the output further.
   • Example:

     SELECT CONCAT(UPPER(first_name), ' ', LOWER(last_name)) AS full_name
     FROM customers;
     

6. Ordering Results Based on Concatenated Values:
   • Sometimes you might want to order your results based on the concatenated string, especially when displaying combined names.
   • Example:

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

Using CONCAT effectively in PostgreSQL helps you manage and present string data in a more organized way, particularly when working with customer or transaction records in a banking system.

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SELECT employee_id, employee_number, first_name || ' ' || last_name AS employee_full_name
FROM org_employee;

SQL CONCAT, combine multiple columns

Example 1 - Raw data from employee table

Example 1 - CONCAT employee first and last name

SELECT
    employee_id, employee_number,
    concat(first_name , ' ' , last_name) as employee_full_name
FROM org_employee;

Example 1 - Query data mapping

The contents of the first_name and last_name columns will be merged to create a unified column, separated by a space.

Example 1 - Query Output

Example 2 - Raw data from client table

Example 2 - CONCAT client name and address

SELECT
    client_id,
    first_name || ' ' || last_name as client_full_name,
    address1 || ', ' || city || ', ' || state || ' '  || postal_code as client_address
FROM org_client

Example 2 - Query data mapping

The first_name and last_name columns will be amalgamated to generate a consolidated column named 'client full name', with a space as the separator. Subsequently, the address, city, state, and zip will be amalgamated to produce the client's address.

Example 2 - Query Output