SQL Server / Oracle Concatenate

Concatenate

Note, when joining two or more fields together, both fields must be a
string value.  If one of the fields is a numeric value, the numeric field
must be converted to a string.

SQL Server:

SELECT Emp_LastName + ', ' + Emp_FirstName FROM Employee;
Returns 'LastName, FirstName'

Oracle:

Two pipe symbols (||) are used to concatenate values in Oracle

SELECT Emp_LastName || ', ' || Emp_FirstName FROM Employee;

The CONCAT Function can only join two strings together.  If you need to
join more than two strings, you will need to use the method above.

SELECT CONCAT(Emp_LastName, Emp_FirstName) FROM Employee;
Returns 'LastName, FirstName'