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database/notes/09-subqueries-views-worksheet-answers.md

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+# Sub-queries and views worksheet
+## Sub-queries
+
+1. Get all the students whose IQ is greater than the average IQ.
+
+```sql
+SELECT 
+    first_name, last_name, iq
+FROM
+    students
+WHERE
+    iq > (SELECT 
+            AVG(iq)
+        FROM
+            students);
+```
+
+2. Get all the students whose IQ is greater than the highest IQ of the batch_id `2` students.
+
+```sql
+SELECT 
+    *
+FROM
+    students
+WHERE
+    iq > (SELECT 
+            MAX(iq)
+        FROM
+            students
+        WHERE
+            batch_id = 2);
+```
+
+3. Get all the students whose IQ is greater than `all` the IQs of the batch_id `2` students.
+
+```sql
+SELECT 
+    *
+FROM
+    students
+WHERE
+    iq > ALL (SELECT 
+            iq
+        FROM
+            students
+        WHERE
+            batch_id = 2);
+```
+
+4. Find all the students who are in batches that start with the word `Jedi` (Without JOIN)
+
+```sql
+SELECT 
+    *
+FROM
+    students
+WHERE
+    batch_id IN (SELECT 
+            id
+        FROM
+            batches
+        WHERE
+            name LIKE 'Jedi%');
+```
+
+5. Find all the students whose IQ is greater than the average IQ of their batch.
+
+```sql
+SELECT 
+    *
+FROM
+    students;
+
+SELECT 
+    first_name, last_name, batch_id, iq
+FROM
+    students s
+WHERE
+    s.iq > (SELECT 
+            AVG(iq)
+        FROM
+            students e
+        WHERE
+            e.batch_id = s.batch_id);
+```
+
+6. Get all the instructors that have at least one batch (Without using joins)
+
+```sql
+SELECT 
+    *
+FROM
+    instructors i
+WHERE
+    EXISTS( SELECT 
+            id
+        FROM
+            batches
+        WHERE
+            instructor_id = i.id);
+```
+
+7. Print all the names, batch ID and average IQ of the batch for each student
+
+```sql
+SELECT 
+    id,
+    first_name,
+    last_name,
+    iq,
+    batch_id,
+    (SELECT 
+            AVG(iq)
+        FROM
+            students
+        WHERE batch_id = s.batch_id     
+		)
+FROM
+    students s;
+```
+
+## Views
+
+1. Create a view that shows the students and their batches.
+
+```sql
+CREATE VIEW students_and_batches AS
+SELECT 
+    s.id,
+    s.first_name,
+    s.last_name,
+    s.iq,
+    b.name AS batch_name
+FROM
+    students s
+        JOIN
+    batches b ON s.batch_id = b.id;
+```
+
+2. Create a view that shows the students and their batches, but only for batches that start with the word `Jedi`.
+
+```sql
+CREATE VIEW students_and_batches AS
+SELECT 
+    s.id,
+    s.first_name,
+    s.last_name,
+    s.iq,
+    b.name AS batch_name
+FROM
+    students s
+        JOIN
+    batches b ON s.batch_id = b.id
+WHERE
+    b.name LIKE 'Jedi%';
+```