Merge pull request #338 from GeoSegun/lateral-subquery

[SQL-242] Lateral Join vs. Subquery

Author: maibin

sql-queries-10/lateral-joins-vs-subqueries/example-usage-lateral-join.sql

@@ -0,0 +1,27 @@
+SELECT 
+    f.id, 
+    f.name, 
+    t.course_id, 
+    t.semester, 
+    t.year
+FROM 
+    Faculty f
+LEFT JOIN LATERAL (
+    SELECT 
+        te.course_id, 
+        te.semester, 
+        te.year
+    FROM 
+        Teaching te
+    WHERE 
+        te.faculty_id = f.id
+    ORDER BY 
+        te.year DESC, 
+        CASE te.semester
+            WHEN 'FALL' THEN 3
+            WHEN 'SUMMER' THEN 2
+            WHEN 'SPRING' THEN 1
+            ELSE 0
+        END DESC
+    LIMIT 1
+) t ON true;

sql-queries-10/lateral-joins-vs-subqueries/example-usage-subqueries.sql

@@ -0,0 +1,17 @@
+SELECT 
+    f.id, 
+    f.name,
+    (
+        SELECT te.course_id
+        FROM Teaching te
+        WHERE te.faculty_id = f.id
+        ORDER BY te.year DESC, 
+            CASE te.semester
+                WHEN 'FALL' THEN 3
+                WHEN 'SUMMER' THEN 2
+                WHEN 'SPRING' THEN 1
+                ELSE 0
+            END DESC
+        LIMIT 1
+    ) AS latest_course_id
+FROM Faculty f;