MIT-Curricular/DBMS/SQL/Week7/writeup.md

## Week 7 - DBMS Lab - PL SQL & Triggers

### Q1. Generate a trigger displaying driver information, on participating in an accident.

Trigger:
```sql
CREATE OR REPLACE TRIGGER trg_display_driver_info
AFTER INSERT ON participated
FOR EACH ROW
DECLARE
    v_driver_name VARCHAR2(100);
    v_driver_address VARCHAR2(255);
BEGIN
    SELECT NAME, ADDRESS
    INTO v_driver_name, v_driver_address
    FROM person
    WHERE DRIVER_ID# = :NEW.DRIVER_ID#;

    DBMS_OUTPUT.PUT_LINE('Driver ID: ' || :NEW.DRIVER_ID#);
    DBMS_OUTPUT.PUT_LINE('Driver Name: ' || v_driver_name);
    DBMS_OUTPUT.PUT_LINE('Driver Address: ' || v_driver_address);
    DBMS_OUTPUT.PUT_LINE('Car Registration Number: ' || :NEW.REGNO);
    DBMS_OUTPUT.PUT_LINE('Report Number: ' || :NEW.REPORT_NUMBER);
    DBMS_OUTPUT.PUT_LINE('Damage Amount: ' || :NEW.DAMAGE_AMOUNT);
END;
/
```

Demo:
```sql
SQL> INSERT INTO participated (DRIVER_ID#, REGNO, REPORT_NUMBER, DAMAGE_AMOUNT)
  2  VALUES (1235, 'EFGH2001', 3, 5000);
Driver ID: 1235
Driver Name: Rohit
Driver Address: Banglalore India
Car Registration Number: EFGH2001
Report Number: 3
Damage Amount: 5000
Driver_id: 1235 Name: Rohit Address: Banglalore India

1 row created.
```

### Q2. Create a trigger that updates a `total_damage` column in the `accident` table whenever a new entry is added to or removed from the participated field.`
Trigger:
```SQL
SQL> CREATE OR REPLACE TRIGGER update_total_damage
  2  AFTER
  3    INSERT OR DELETE ON PARTICIPATED
  4  BEGIN
  5    UPDATE ACCIDENT
  6    SET
  7      total_damage = (
  8        SELECT
  9          SUM(damage_amount)
 10        FROM PARTICIPATED p
 11        WHERE
 12          p.report_number = ACCIDENT.report_number
 13      );
 14  END;
 15  /

Trigger created.
```
Adding an identifier `total_damage`:
```sql
SQL> ALTER TABLE ACCIDENT ADD total_damage NUMBER;
```
Test case with Insertion:
```sql
SQL> INSERT INTO
        PARTICIPATED (driver_id#, regno, report_number, damage_amount)
      VALUES
        ('1235', 'EFGH2001', 1, 5000);
Driver_id: 1235 Name: Rohit Address: Banglalore India

1 row created.

SQL> SELECT
        report_number,
        total_damage
      FROM ACCIDENT
      WHERE
        report_number = 1;

REPORT_NUMBER TOTAL_DAMAGE
------------- ------------
            1        15000
```
Test case with Deletion:
```sql
SQL> DELETE FROM PARTICIPATED
      WHERE
        driver_id# = '1235'
        AND regno = 'EFGH2001'
        AND report_number = 1;

1 row deleted.

SQL> SELECT
        report_number,
        total_damage
      FROM ACCIDENT
      WHERE
        report_number = 1;

REPORT_NUMBER TOTAL_DAMAGE
------------- ------------
            1        10000
```


### Q3. List cars involved in accidents with cumulative damage exceeding a specific amount.

Checking for damage amount > 10000, we have
```SQL
SQL> SELECT
          p.driver_id#,
          o.regno,
          SUM(pa.damage_amount) AS total_damage
      FROM
          PARTICIPATED pa
      JOIN
          OWNS o ON pa.driver_id# = o.driver_id#
      JOIN
          PERSON p ON o.driver_id# = p.driver_id#
      GROUP BY
          p.driver_id#, o.regno
      HAVING
          SUM(pa.damage_amount) > 10000;

DRIVER_ID#                     REGNO                TOTAL_DAMAGE
------------------------------ -------------------- ------------
1238                           HFSP5601                    26500
```

### Q4. Identify cars that have been involved in more than one accident and calculate the total damage for each car.

```SQL
SQL> SELECT 
    o.regno, 
    COUNT(DISTINCT pa.report_number) AS accident_count, 
    SUM(pa.damage_amount) AS total_damage
FROM 
    PARTICIPATED pa
JOIN 
    OWNS o ON pa.driver_id# = o.driver_id#
GROUP BY 
    o.regno
HAVING 
    COUNT(DISTINCT pa.report_number) > 1;

REGNO                ACCIDENT_COUNT TOTAL_DAMAGE
-------------------- -------------- ------------
HFSP5601                          2        26500
```

### Q5. Calculate the average damage amount for accidents at each location.
```sql
SQL> SELECT
          a.location,
          AVG(pa.damage_amount) AS average_damage
      FROM
          ACCIDENT a
      JOIN
          PARTICIPATED pa ON a.report_number = pa.report_number
      GROUP BY
          a.location;

LOCATION                                           AVERAGE_DAMAGE
-------------------------------------------------- --------------
 karnataka India                                            25000
Delhi India                                                 10000
 India                                                       2575
 Gujrat India                                                1500
 ```