Update for 28-02-22 16:45

tech/sql.wiki

@@ -34,7 +34,68 @@ will return all bands with the string 'light' in their name.
 
 === DISTINCT ===
 
-`DISTINCT` filters results by only returning unique values in a column
+`DISTINCT` filters results by only returning unique values of a column.
+Therefore, we can only be used to return a single column.
+
+{{{
+SELECT DISTINCT nationality FROM users;
+  }}}
+
+== Presentation ==
+
+=== Order by ===
+
+`ORDER BY` allows us to descide how the query will be shown. For example,
+
+{{{
+SELECT Firstname, Lastname
+FROM users
+ORDER BY Lastname [SORT];
+  }}}
+
+where `[SORT]` is
+
+* DESC
+  * descending order
+* ASC
+  * ascending order
+
+=== CASE ===
+
+Case is a statement block where we can choose exactly what text is returned
+based on values in the database.
+
+{{{
+SELECT Name,
+CASE
+    WHEN Country = 'USA' THEN 'North America'
+    WHEN Country = 'UK' THEN 'Europe'
+    ELSE 'Wolrd'
+END
+FROM Users;
+  }}}
+
+=== LIMIT ===
+
+`LIMIT` allows us to retstrict the number or rows returned.
+
+`SELECT * FROM users ORDER BY name DESC LIMIT 1`
+
+=== COUNT ===
+
+If we want just the number of rows, we can use count.
+
+`SELECT COUNT(*) FROM users WHERE dob > '2000-01-01'`
+
+=== math functions ===
+
+If we want to sum the values in ONE column we can use sum
+
+`SELECT SUM(cash_balance) FROM users`
+
+If we want to find an average,
+
+`SELECT AVG(price) FROM products`
 
 == Views ==