Update for 03-03-22 22:00

tech/sql.wiki

@@ -109,6 +109,26 @@ grouping totals based upon some other row.
 
 `SELECT Team, COUNT(*) FROM Players GROUP BY Team`
 
+=== JOIN ===
+
+`JOIN` allows two tables to be returned together, where they are 'joined' upon
+a shared field.
+
+{{{
+SELECT Orders.ID, Customers.Name, Orders.Name
+FROM Orders
+INNER JOIN Customers ON Orders.CustomerId=Customers.Id
+  }}}
+
+There are four types of joins
+* `INNER JOIN` returns all records that having matching records in both tables
+* `LEFT OUTER JOIN` returns all records from the left (Orders in above example)
+  table, and the matched records from the right table
+* `RIGHT OUTER JOIN` returns all records from the right (Customers in above
+  example) table, and the matched records from the left table
+* `FULL OUTER JOIN` returns all records when there is a match in either the
+  left or right table
+
 == Views ==
 
 A view can be created with the following command