Add Use Variables In An Anonymous Function as a Postgres TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1323 TILs and counting..._
+_1324 TILs and counting..._
 
 ---
 
@@ -740,6 +740,7 @@ _1323 TILs and counting..._
 - [Use Argument Indexes](postgres/use-argument-indexes.md)
 - [Use Not Valid To Immediately Enforce A Constraint](postgres/use-not-valid-to-immediately-enforce-a-constraint.md)
 - [Use Rename To Hot Swap Two Tables](postgres/use-rename-to-hot-swap-two-tables.md)
+- [Use Variables In An Anonymous Function](postgres/use-variables-in-an-anonymous-function.md)
 - [Using Expressions In Indexes](postgres/using-expressions-in-indexes.md)
 - [Using Intervals To Offset Time](postgres/using-intervals-to-offset-time.md)
 - [Who Is The Current User](postgres/who-is-the-current-user.md)

postgres/use-variables-in-an-anonymous-function.md

@@ -0,0 +1,42 @@
+# Use Variables In An Anonymous Function
+
+I was curious how variables could be declared and used in PostgreSQL, so I did
+a little experiment with a `books` and `authors` schema.
+
+Variables need to be declared and used within the context of a function. Using
+the [`do` syntax](https://www.postgresql.org/docs/9.1/sql-do.html) I am able to
+declare and execute an anoymous code block.
+
+Within that code block I can declare one or more variables by giving them a
+type and optionally a default value. Below I declare `author_id` with a default
+and `result` as a `record` type.
+
+```sql
+do $$
+declare
+  author_id varchar := 'e2b42ebf-7ea9-4d9e-8edf-310fc1894bcd';
+  result record;
+begin
+  for result in select title from books where "authorId" = author_id
+  loop
+    raise notice '| % |', result.title;
+  end loop;
+end $$;
+```
+
+I'm able to use the `author_id` variable directly in a `select` statement.
+
+```sql
+select title from books where "authorId" = author_id
+```
+
+and then using a [for
+loop](https://www.postgresql.org/docs/current/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING)
+with my `result` of `record` type, I can iterate over each of the results from
+the `select`.
+
+Because this anonymous `do` block implicitly has a `void` return type, I need
+to do something with the result within the block. For demonstration purposes, I
+use [`raise
+notice`](https://www.postgresql.org/docs/current/plpgsql-errors-and-messages.html)
+to log out each book title.