Creating functions in SQL

Creating functions can be complex but like anything else, it becomes easier with practice. Let’s look through a few of the steps in detail:

1. Begin with CREATE OR REPLACE FUNCTION. This is where you name your function.
2. Next, define the function parameter(s) within parentheses.
3. Insert the RETURNS TABLE function, followed by the data type. This is a text option as the actual function will add the variable when it is run.
4. Now, select the language property of SQL as PostgreSQL since it is not limited by a single procedural language.
5. The actual query will now be included inside $$ query $$. These are called dollar-quoted string constants ($$).

We need to create the function (as shown in the following code) and then pass to the function what we want it to do.

First, we want to select boundary_protected_area, which is where highways intersect. We are passing text (x text), which counts as one variable. The text is entered when...