Update 02-sql-aggregation.md

This addresses #284. I also split up table and column aliases to make the difference clearer (I totally missed the table alias during the first read through!), and added a tiny bit more explanation.

episodes/02-sql-aggregation.md

@@ -117,21 +117,33 @@ species captured, ordered by the count:
 
 ## Aliases
 
-As queries get more complex names can get long and unwieldy. To help make things
-clearer we can use aliases to assign new names to things in the query.
+As queries get more complex, the expressions we use can get long and unwieldy. To help make things
+clearer in the query and in its output, we can use aliases to assign new names to things in the query. 
 
-We can use aliases in column names or table names using `AS`:
+We can use aliases in column names using `AS`:
 
     SELECT MAX(year) AS last_surveyed_year
     FROM surveys;
 
 The `AS` isn't technically required, so you could do
 
-    SELECT MAX(year) yr
-    FROM surveys surv;
+    SELECT MAX(year) last_surveyed_year
+    FROM surveys;
 
 but using `AS` is much clearer so it is good style to include it.
 
+We can not only alias column names, but also table names in the same way:
+
+    SELECT *
+    FROM surveys AS surv;
+    
+And again, the `AS` keyword is not required, so this works, too:
+
+    SELECT *
+    FROM surveys surv;
+
+Aliasing table names can be helpful when working with queries that involve multiple tables; you will learn more about this later.
+
 ## The `HAVING` keyword
 
 In the previous episode, we have seen the keyword `WHERE`, allowing to