Oracle

In Oracle, the CONCAT function is used in Data Query Language (DQL) to join two strings together. It is often used when you want to combine text data from different columns or add static text to existing data in a query. Note that CONCAT only allows two arguments at a time, but if you need to concatenate more than two strings, you can nest the CONCAT function or use the || operator, which is an alternative for string concatenation.

Here’s a breakdown of how to use CONCAT in Oracle:

1. Basic Syntax of CONCAT:

   • The basic syntax for CONCAT is as follows:

     CONCAT(string1, string2)
     

     • string1: The first string or column to concatenate.
     • string2: The second string or column to concatenate.

2. Example with Database Tables:
   Consider the following authors table:

   author_id	first_name	last_name
   1	John	Doe
   2	Jane	Austen

   To concatenate the first name and last name of the authors, you can use the CONCAT function:

   SELECT CONCAT(first_name, last_name) AS full_name
   FROM authors;
   

   • This query will return:
     • JohnDoe
     • JaneAusten

3. Using CONCAT with Spaces:
   If you want to add a space between the first name and last name, you can nest the CONCAT function or use the || operator:

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

   • The output will now show:
     • John Doe
     • Jane Austen

4. Concatenating More than Two Strings:
   When you need to concatenate more than two strings, you can either nest the CONCAT function or use the || operator. For example, to concatenate the first name, a space, and the last name:

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

   Or:

   SELECT first_name || ' ' || last_name AS full_name
   FROM authors;
   

5. Using CONCAT in WHERE Clause:
   You can also use CONCAT in a WHERE clause. For example, if you want to find an author whose full name is "John Doe":

   SELECT *
   FROM authors
   WHERE CONCAT(first_name, ' ' || last_name) = 'John Doe';
   

6. Best Practices:

   • Use the || operator for concatenating more than two strings for better readability.
   • Always ensure the data types being concatenated are strings; if not, convert them using TO_CHAR to avoid errors.
   • Avoid concatenating large amounts of data directly in the query for performance reasons.

By following these practices, you will be able to use CONCAT effectively in Oracle queries to combine text data.

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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