What is the method in SQL for concatenating two columns into one column?

In SQL, two columns can be joined into one column by using the string concatenation function CONCAT() or using the + operator for concatenation.

Syntax for using the CONCAT() function is as follows:

SELECT CONCAT(column1, column2) AS new_column_name
FROM table_name;

The syntax for using the + operator is as follows:

SELECT column1 || column2 AS new_column_name
FROM table_name;

In the above syntax, column1 and column2 are the two columns to be joined, new_column_name is the newly created column name, and table_name is the table to be queried.