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database/notes/08-window-functions-worksheet-answers.md

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+# Window functions worksheet
+
+1. Print the student names along with the number of students in their batch.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    COUNT(*) OVER (PARTITION BY batch_id) AS batch_size
+FROM
+    students;
+```
+
+2. Print the student names along with the average IQ of their batch.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    AVG(iq) OVER (PARTITION BY batch_id) AS batch_avg_iq
+FROM
+    students;
+```
+
+3. Print the student names along with the maximum IQ of their batch.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    MAX(iq) OVER (PARTITION BY batch_id) AS batch_max_iq
+FROM
+    students;
+```
+
+4. Print the student names along with their rank based on IQ.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    RANK() OVER (ORDER BY iq) AS iq_rank
+FROM
+    students;
+```
+
+5. Print the student names along with their rank in their batch based on IQ.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    RANK() OVER (PARTITION BY batch_id ORDER BY iq) AS batch_iq_rank
+FROM
+    students;
+```
+
+6. Print the student names along with their rank in their batch based on IQ. Ties should not increase the rank.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    DENSE_RANK() OVER (PARTITION BY batch_id ORDER BY iq) AS batch_iq_rank
+FROM
+    students;
+```
+
+7. Print the student names along with their rank in their batch based on IQ. Ties should not be counted and broken by ID.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    batch_id,
+    iq,
+    ROW_NUMBER() OVER (PARTITION BY batch_id ORDER BY iq, id) AS batch_iq_rank
+FROM 
+    students;
+```
+
+8. Find the rank of batches based on the start date of the batch.
+
+```sql
+SELECT 
+    id, 
+    name,
+    start_date,
+    RANK() OVER (ORDER BY start_date) AS batch_rank
+FROM
+    batches;
+```
+
+9. Sort the instructors by the first and last name and assign them a roll number.
+
+```sql
+SELECT 
+    id, 
+    first_name,
+    last_name,
+    ROW_NUMBER() OVER (ORDER BY first_name, last_name) AS roll_number
+FROM
+    instructors;
+```