Differences

This shows you the differences between two versions of the page.

--- db-class-excerpt [2011/10/10 10:35] – created dblume
+++ db-class-excerpt [2023/04/12 20:44] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ===== Relational Algebra 2 =====
-**Union** Operator: Problem with × and ⋈ is that they try to match tuples (rows) form the relations (tables).  Here, we combine the information vertically.
+**Union** Operator: Problem with × (cross product) and ⋈ (natural joins) is that they try to match tuples (rows) form the relations (tables).  Here, we combine the information vertically.
 π<sub>cName</sub> College ∪ π<sub>sName</sub> Student gives:
-Stanford\\
+Stanford
-Susan\\
+Susan
-Cornell\\
+Cornell
-Mary\\
+Mary
-John\\
+John
 ...