Updates readme

README.md

@@ -26,11 +26,12 @@ Or install it yourself as:
 
 ## Usage
 
-Just `require 'postgres_ext'` and use ActiveRecord as you normally would! postgres_ext extends
+Just `require 'postgres_ext'` and use ActiveRecord as you normally would! postgres\_ext extends
 ActiveRecord's data type handling.
 
  * [Migration/Schema.rb support](#migrationschemarb-support)
  * [Type Casting support](#type-casting-support)
+ * [Querying PostgreSQL datatypes](#querying-postgresql-datatypes)
 
 ### Usage Notes
 Take care when dealing with arrays and other types that allow you to
@@ -157,6 +158,74 @@ person_2.favorite_numbers.first.class
 # => Fixnum
 ```
 
+## Querying PostgreSQL datatypes
+
+  * Arrays
+  * INET/CIDR
+
+### Arrays
+
+  * && - Array Overlap operator
+  * ANY or ALL functions
+
+#### && - Array Overlap operator
+
+PostgreSQL implements the `&&` operator, known as the overlap operator,
+for arrays. The overlap operator returns `t` (true) when two arrays have
+one or more elements in common.
+
+```sql
+ARRAY[1,2,3] && ARRAY[4,5,6]
+-- f
+
+ARRAY[1,2,3] && ARRAY[3,5,6]
+-- t
+```
+
+Postgres\_ext defines `array_overlap`, an ARel predicate for the `&&` operator.
+
+```ruby
+user_arel = User.arel_table
+
+User.where(user_arel[:tags].array_overlap(['one','two'])).to_sql
+# => SELECT \"users\".* FROM \"users\" WHERE \"users\".\"tags\" && '{one,two}'
+```
+
+#### ANY or ALL function
+
+When querying array columns, you have the ability to see if a predicate
+apply's to either *any* element in the array, or *all* elements of the
+array. The syntax for these predicates are slightly different then the
+normal `where` syntax in PostgreSQL. To see if an array contains the
+string `'test'` in any location, you would write the following in SQL
+
+```sql
+SELECT *
+FROM users
+WHERE 'test' = ANY(users.tags)
+```
+
+Notice that the column is on the right hand side of the predicate,
+instead of the left, because we have to call the `ANY` function on that
+column.
+
+We can generate the above query using [Arel](https://github.com/rails/arel)
+and generating the Node manually. We would use the following to
+accompish this:
+
+```ruby
+user_arel = User.arel_table
+
+any_tags_function = Arel::Nodes::NamedFunction.new('ANY', [user_arel[:tags]])
+predicate = Arel::Nodes::Equality('test', any_tags_function)
+
+User.where(predicate).to_sql
+#=> SELECT \"users\".* FROM \"users\" WHERE 'test' = ANY(\"users\".\"tags\")
+
+```
+
+The ALL version of this same predicate can be generated by swap `'ANY'`
+for `'ALL'` in the named function.
 
 ## Authors