Add Get An Array Of Values From The Database as a rails til

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_886 TILs and counting..._
+_887 TILs and counting..._
 
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@@ -531,6 +531,7 @@ _886 TILs and counting..._
 - [Disambiguate Where In A Joined Relation](rails/disambiguate-where-in-a-joined-relation.md)
 - [Ensure Migrations Use The Latest Schema](rails/ensure-migrations-use-the-latest-schema.md)
 - [Generating And Executing SQL](rails/generating-and-executing-sql.md)
+- [Get An Array Of Values From The Database](rails/get-an-array-of-values-from-the-database.md)
 - [Get The Column Names For A Model](rails/get-the-column-names-for-a-model.md)
 - [Hash Slicing](rails/hash-slicing.md)
 - [Ignore Poltergeist JavaScript Errors](rails/ignore-poltergeist-javascript-errors.md)

rails/get-an-array-of-values-from-the-database.md

@@ -0,0 +1,40 @@
+# Get An Array Of Values From The Database
+
+We generally get data from our database through [ActiveRecord
+models](https://api.rubyonrails.org/classes/ActiveRecord/Base.html):
+
+```ruby
+> Product.where(available: true).pluck(:sku)
+[ "efg-1234", "pqr-3455", ... ]
+```
+
+If we need to do a more specialized query, we might reach for
+[`execute`](https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/DatabaseStatements.html#method-i-execute):
+
+```ruby
+> ActiveRecord::Base.connection.execute(<<-SQL)
+    select split_part(sku, '-', 1) product_type
+      from products
+      where available = true;
+  SQL
+[{ "product_type" => "efg" }, { "product_type" => "pqr" }, ... ]
+```
+
+The results are bundled up in a predictable, but verbose array of hashes.
+
+We could trim the result down to just the values using either
+[`select_values`](https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/DatabaseStatements.html#method-i-select_values)
+or
+[`select_rows`](https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/DatabaseStatements.html#method-i-select_rows):
+
+```ruby
+> ActiveRecord::Base.connection.select_values(<<-SQL)
+    select split_part(sku, '-', 1) product_type
+      from products
+      where available = true;
+  SQL
+[ "efg", "pqr", ... ]
+```
+
+If the SQL statement is to return more than one row in the result, then you'll
+want `select_rows` instead of `select_values`.