ADVANCED
DATABASE MANAGEMENT SYSTEMS
UNIT
III
Basic
Structure of SQL Queries - Additional Basics Operations, Set Operations - Null
Values, Aggregate Functions - Nested Subqueries, Modification of the Database
SQL
QUESTION BANK
Units
Covered:
1️⃣ OBJECTIVE TYPE QUESTIONS (MCQs)
1.
Which SQL command is used to create a table?
a) INSERT
b) UPDATE
c) CREATE
d) SELECT
✅ Answer:
c) CREATE
2.
Which clause is used to filter records in SQL?
a) ORDER BY
b) WHERE
c) GROUP BY
d) HAVING
✅ Answer:
b) WHERE
3.
Which set operation returns common records from two queries?
a) UNION
b) INTERSECT
c) MINUS
d) ALL
✅ Answer:
b) INTERSECT
4.
Which aggregate function returns the total number of rows?
a) SUM()
b) AVG()
c) COUNT()
d) MAX()
✅ Answer:
c) COUNT()
5.
Which keyword is used to handle missing or unknown values?
a) DEFAULT
b) NULL
c) VOID
d) EMPTY
✅ Answer:
b) NULL
2️⃣ FILL IN THE BLANKS
3️⃣ BLOOM’S TAXONOMY QUESTIONS WITH
ANSWERS
🔹 Remembering
Q: List any four SQL DDL commands.
A: CREATE, DROP, ALTER, TRUNCATE
🔹 Understanding
Q: Explain the purpose of the WHERE
clause.
A: The WHERE clause filters records based on specified conditions.
🔹 Applying
Q: Write a SQL query to display all
students with marks greater than 80.
A:
SELECT *
FROM student WHERE marks > 80;
🔹 Analyzing
Q: Differentiate between WHERE and
HAVING clauses.
A:
🔹 Evaluating
Q: Why are nested subqueries
preferred in complex queries?
A: They improve query clarity, reusability, and allow conditional
filtering.
🔹 Creating
Q: Create a table Employee with
EmpID, Name, and Salary.
A:
CREATE
TABLE Employee (
EmpID INT,
Name VARCHAR(50),
Salary DECIMAL(10,2)
);
4️⃣ DETAILED ANSWERS (THEORY +
EXAMPLES)
📘 Data Definition Language (DDL)
DDL
commands define database structure.
Commands:
Example:
CREATE
TABLE Student (
RollNo INT,
Name VARCHAR(30),
Age INT
);
📘 Basic Structure of SQL Queries
SELECT
column_name
FROM
table_name
WHERE
condition;
Example:
SELECT
Name FROM Student WHERE Age > 18;
📘 Additional Basic Operations
📘 Set Operations
|
Operation |
Description |
|
UNION |
Combines
results, removes duplicates |
|
UNION
ALL |
Keeps
duplicates |
|
INTERSECT |
Common
records |
|
MINUS |
Records
in first query only |
📘 NULL Values
NULL
represents missing or unknown data.
Checking
NULL:
SELECT *
FROM Student WHERE Age IS NULL;
📘 Aggregate Functions
Example:
SELECT
AVG(Salary) FROM Employee;
📘 Nested Subqueries
A query
inside another query.
Example:
SELECT
Name FROM Employee
WHERE
Salary > (SELECT AVG(Salary) FROM Employee);
📘 Modification of the Database
Example:
UPDATE
Employee SET Salary = 50000 WHERE EmpID = 101;
SQL
QUERIES WITH EXAMPLES
(Based
on syllabus)
1️⃣ DATA DEFINITION LANGUAGE (DDL)
🔹 CREATE TABLE
Purpose: Create a new table
CREATE
TABLE Student (
RollNo INT,
Name VARCHAR(30),
Age INT,
Marks INT
);
Example:
Creates a table named Student with four columns.
🔹 ALTER TABLE
Purpose: Modify table structure
ALTER
TABLE Student ADD Email VARCHAR(50);
Example:
Adds a new column Email to Student table.
🔹 DROP TABLE
Purpose: Delete table permanently
DROP TABLE
Student;
Example:
Removes the Student table completely.
🔹 TRUNCATE TABLE
Purpose: Remove all records (structure
remains)
TRUNCATE
TABLE Student;
2️⃣ BASIC STRUCTURE OF SQL QUERY
🔹 SELECT Statement
SELECT *
FROM Student;
Example:
Displays all records from Student table.
🔹 SELECT with WHERE
SELECT
Name, Marks FROM Student WHERE Marks > 80;
Example:
Shows students scoring more than 80 marks.
3️⃣ ADDITIONAL BASIC OPERATIONS
🔹 ORDER BY
SELECT *
FROM Student ORDER BY Marks DESC;
Example:
Displays students sorted by marks (highest first).
🔹 DISTINCT
SELECT
DISTINCT Age FROM Student;
Example:
Displays unique ages only.
🔹 LIKE Operator
SELECT *
FROM Student WHERE Name LIKE 'A%';
Example:
Displays names starting with letter A.
4️⃣ SET OPERATIONS
Assume two
tables:
ClassA and ClassB
🔹 UNION
SELECT
Name FROM ClassA
UNION
SELECT
Name FROM ClassB;
Example:
Combines names from both tables (no duplicates).
🔹 UNION ALL
SELECT
Name FROM ClassA
UNION ALL
SELECT
Name FROM ClassB;
Example:
Includes duplicate names.
🔹 INTERSECT
SELECT
Name FROM ClassA
INTERSECT
SELECT
Name FROM ClassB;
Example:
Displays common students.
🔹 MINUS
SELECT
Name FROM ClassA
MINUS
SELECT
Name FROM ClassB;
Example:
Students only in ClassA.
5️⃣ NULL VALUES
🔹 IS NULL
SELECT *
FROM Student WHERE Email IS NULL;
Example:
Shows students without email ID.
🔹 IS NOT NULL
SELECT *
FROM Student WHERE Email IS NOT NULL;
6️⃣ AGGREGATE FUNCTIONS
🔹 COUNT()
SELECT
COUNT(*) FROM Student;
Example:
Counts total number of students.
🔹 SUM()
SELECT
SUM(Marks) FROM Student;
🔹 AVG()
SELECT
AVG(Marks) FROM Student;
🔹 MAX() and MIN()
SELECT
MAX(Marks), MIN(Marks) FROM Student;
7️⃣ NESTED SUBQUERIES
🔹 Subquery with SELECT
SELECT
Name FROM Student
WHERE
Marks > (SELECT AVG(Marks) FROM Student);
Example:
Displays students scoring above average marks.
🔹 Subquery with IN
SELECT
Name FROM Student
WHERE
RollNo IN (SELECT RollNo FROM Result WHERE Status = 'Pass');
8️⃣ MODIFICATION OF DATABASE
🔹 INSERT
INSERT
INTO Student VALUES (1, 'Ravi', 20, 85);
🔹 UPDATE
UPDATE
Student SET Marks = 90 WHERE RollNo = 1;
🔹 DELETE
DELETE
FROM Student WHERE Marks < 40;
SQL
QUERIES WITH INPUT DATA & OUTPUT
📘 ASSUME STUDENT TABLE DATA
SELECT *
FROM Student;
|
RollNo |
Name |
Age |
Marks |
Email |
|
1 |
Ravi |
20 |
85 |
|
|
2 |
Anu |
19 |
92 |
NULL |
|
3 |
Kumar |
21 |
70 |
|
|
4 |
Asha |
20 |
40 |
NULL |
|
5 |
Bala |
22 |
95 |
1️⃣ BASIC SELECT QUERY
SELECT *
FROM Student;
✅ OUTPUT
|
RollNo |
Name |
Age |
Marks |
Email |
|
1 |
Ravi |
20 |
85 |
|
|
2 |
Anu |
19 |
92 |
NULL |
|
3 |
Kumar |
21 |
70 |
|
|
4 |
Asha |
20 |
40 |
NULL |
|
5 |
Bala |
22 |
95 |
2️⃣ SELECT WITH WHERE
SELECT
Name, Marks FROM Student WHERE Marks > 80;
✅ OUTPUT
|
Name |
Marks |
|
Ravi |
85 |
|
Anu |
92 |
|
Bala |
95 |
3️⃣ ORDER BY
SELECT
Name, Marks FROM Student ORDER BY Marks DESC;
✅ OUTPUT
|
Name |
Marks |
|
Bala |
95 |
|
Anu |
92 |
|
Ravi |
85 |
|
Kumar |
70 |
|
Asha |
40 |
4️⃣ DISTINCT
SELECT
DISTINCT Age FROM Student;
✅ OUTPUT
|
Age |
|
19 |
|
20 |
|
21 |
|
22 |
5️⃣ LIKE OPERATOR
SELECT
Name FROM Student WHERE Name LIKE 'A%';
✅ OUTPUT
|
Name |
|
Anu |
|
Asha |
6️⃣ NULL VALUES
SELECT
Name FROM Student WHERE Email IS NULL;
✅ OUTPUT
|
Name |
|
Anu |
|
Asha |
7️⃣ AGGREGATE FUNCTIONS
🔹 COUNT
SELECT
COUNT(*) FROM Student;
✅ OUTPUT
|
COUNT(*) |
|
5 |
🔹 SUM
SELECT
SUM(Marks) FROM Student;
✅ OUTPUT
|
SUM(Marks) |
|
382 |
🔹 AVG
SELECT
AVG(Marks) FROM Student;
✅ OUTPUT
|
AVG(Marks) |
|
76.4 |
🔹 MAX & MIN
SELECT
MAX(Marks), MIN(Marks) FROM Student;
✅ OUTPUT
|
MAX(Marks) |
MIN(Marks) |
|
95 |
40 |
8️⃣ NESTED SUBQUERY
SELECT
Name FROM Student
WHERE
Marks > (SELECT AVG(Marks) FROM Student);
✅ OUTPUT
|
Name |
|
Ravi |
|
Anu |
|
Bala |
9️⃣ INSERT QUERY
INSERT
INTO Student VALUES (6, 'Sita', 19, 88, 'sita@gmail.com');
✅ OUTPUT (After Insert)
|
RollNo |
Name |
Age |
Marks |
Email |
|
6 |
Sita |
19 |
88 |
🔟 UPDATE QUERY
UPDATE
Student SET Marks = 90 WHERE RollNo = 1;
✅ OUTPUT (Updated Row)
|
RollNo |
Name |
Marks |
|
1 |
Ravi |
90 |
1️⃣1️⃣ DELETE QUERY
DELETE
FROM Student WHERE Marks < 50;
✅ OUTPUT (Remaining Records)
|
RollNo |
Name |
Marks |
|
1 |
Ravi |
90 |
|
2 |
Anu |
92 |
|
3 |
Kumar |
70 |
|
5 |
Bala |
95 |
|
6 |
Sita |
88 |
Intermediate SQL: Join Expression, Views -
Transactions, Integrity Constraints - Data Types and Schemas, Authorization
INTERMEDIATE SQL – COMPLETE QUESTION BANK
Syllabus Covered:
1️⃣ OBJECTIVE TYPE QUESTIONS (MCQs)
1. Which SQL join returns only matching
rows from both tables?
a) LEFT JOIN
b) RIGHT JOIN
c) FULL JOIN
d) INNER JOIN
✅ Answer: d) INNER
JOIN
2. Which command is used to create a view?
a) CREATE TABLE
b) CREATE VIEW
c) ALTER VIEW
d) DROP VIEW
✅ Answer: b) CREATE
VIEW
3. Which command permanently saves
transaction changes?
a) ROLLBACK
b) SAVEPOINT
c) COMMIT
d) DELETE
✅ Answer: c) COMMIT
4. PRIMARY KEY constraint ensures that a
column is
a) NULL
b) Duplicate
c) Unique and NOT NULL
d) Indexed only
✅ Answer: c) Unique
and NOT NULL
5. Which SQL statement is used to grant
permission to a user?
a) REVOKE
b) ALLOW
c) GRANT
d) AUTHORIZE
✅ Answer: c) GRANT
2️⃣ FILL IN THE BLANKS
1.
A ______ join returns all rows from the
left table and matching rows from the right table.
✅ Answer: LEFT JOIN
2.
A view is a ______ table based on SQL
query.
✅ Answer: virtual
3.
The ______ command undoes changes in a
transaction.
✅ Answer: ROLLBACK
4.
FOREIGN KEY constraint maintains ______
integrity.
✅ Answer:
referential
5.
The GRANT command gives ______ to users.
✅ Answer:
privileges
3️⃣ BLOOM’S TAXONOMY QUESTIONS &
ANSWERS
🔹
Remembering
Q: List different types of
SQL joins.
A: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN
🔹
Understanding
Q: Explain views in SQL.
A: A view is a virtual table created using a SELECT query to simplify
complex queries.
🔹
Applying
Q: Write a SQL query to
join Student and Department tables.
A:
SELECT Student.Name, Department.DeptName
FROM Student
INNER JOIN Department
ON Student.DeptID = Department.DeptID;
🔹
Analyzing
Q: Compare INNER JOIN and
LEFT JOIN.
A:
🔹
Evaluating
Q: Why are transactions
important in databases?
A: They ensure data consistency and allow rollback during errors.
🔹
Creating
Q: Create a view for
students scoring above 80 marks.
A:
CREATE VIEW HighScorers AS
SELECT Name, Marks FROM Student WHERE Marks > 80;
4️⃣ EXAMPLES WITH QUERY AND OUTPUT
📘
ASSUME TABLE DATA
Student Table
|
RollNo |
Name |
DeptID |
Marks |
|
1 |
Ravi |
101 |
85 |
|
2 |
Anu |
102 |
90 |
|
3 |
Kumar |
101 |
70 |
Department Table
|
DeptID |
DeptName |
|
101 |
CSE |
|
102 |
IT |
🔹
JOIN EXPRESSION (INNER JOIN)
SELECT Name, DeptName
FROM Student
INNER JOIN Department
ON Student.DeptID = Department.DeptID;
✅
OUTPUT
|
Name |
DeptName |
|
Ravi |
CSE |
|
Anu |
IT |
|
Kumar |
CSE |
🔹
VIEW
CREATE VIEW TopStudents AS
SELECT Name, Marks FROM Student WHERE Marks > 80;
SELECT * FROM TopStudents;
✅
OUTPUT
|
Name |
Marks |
|
Ravi |
85 |
|
Anu |
90 |
🔹
TRANSACTION
BEGIN TRANSACTION;
UPDATE Student SET Marks = 95 WHERE RollNo = 1;
ROLLBACK;
✅
OUTPUT
Marks remain unchanged after rollback.
|
RollNo |
Name |
Marks |
|
1 |
Ravi |
85 |
🔹
INTEGRITY CONSTRAINTS
CREATE TABLE Course (
CourseID INT
PRIMARY KEY,
CourseName
VARCHAR(30) NOT NULL,
DeptID INT,
FOREIGN KEY
(DeptID) REFERENCES Department(DeptID)
);
🔹
DATA TYPES & SCHEMA
CREATE SCHEMA College;
CREATE TABLE College.Faculty (
FacID INT,
Name
VARCHAR(30),
Salary
DECIMAL(10,2));
🔹
AUTHORIZATION
GRANT SELECT, INSERT ON Student TO User1;
REVOKE INSERT ON Student FROM User1;
Advanced SQL: Accessing SQL from Programming Language,
Functions and Procedures, Triggers
All are framed around Oracle‑style PL/SQL (you
can adapt to PostgreSQL/SQL Server if needed).
1. Objective‑type questions (MCQs)
A. Accessing SQL from a programming
language
1.
Which of the following is used to embed
SQL statements directly inside a host programming language like C or Java?
a) Dynamic SQL
b) Embedded SQL
c) Native SQL
d) Inline SQL
2.
In JDBC, which interface is used to call a
stored procedure?
a) Statement
b) PreparedStatement
c) CallableStatement
d) Connection
3.
Which of the following is not a way
to access SQL from a host language?
a) ODBC
b) JDBC
c) PL/SQL blocks only
d) Embedded SQL
4.
What is the main advantage of using stored
procedures instead of plain SQL in the application?
a) Faster network transfer
b) Better security and code reuse
c) Simpler UI design
d) Easier debugging in the browser
Answers:
1.
b) Embedded SQLsanfoundry+1
2.
c) CallableStatement[sanfoundry]
3.
c) PL/SQL blocks onlydb-book+1
4.
b) Better security and code reusedevitpl+1
B. Functions and Procedures
5.
A PL/SQL function must return:
a) A table
b) A cursor
c) A value of a specified data type
d) Nothing
6.
Which keyword is used to define a PL/SQL
procedure?
a) FUNCTION
b) PROCEDURE
c) SUBPROGRAM
d) ROUTINE
7.
Which of the following is true about
PL/SQL functions?
a) They can be called only inside PL/SQL blocks
b) They can be used in SQL SELECT clauses
c) They cannot have parameters
d) They always modify the database
8.
What is the purpose of IN, OUT, and IN OUT
in PL/SQL parameter modes?
a) To specify data types
b) To specify the direction of parameter passing
c) To specify table names
d) To specify transaction behavior
Answers:
5. c) A value of a specified data typesimplilearn+1
6. b) PROCEDUREgeeksforgeeks+1
7. b) They can be used in SQL SELECT clausessimplilearn+1
8. b) To specify the direction of parameter passinggeeksforgeeks+1
C. Triggers
9.
A trigger is automatically executed when:
a) A user logs in
b) A specific SQL event occurs on a table
c) A stored procedure is compiled
d) The database starts
10.
Which of the following is not a
valid trigger timing in Oracle?
a) BEFORE
b) AFTER
c) INSTEAD OF
d) DURING
11.
A row‑level trigger fires:
a) Once per statement
b) Once per row affected by the statement
c) Only on SELECT
d) Only on DROP
12.
Which of the following is a typical use of
a trigger?
a) To create a new table
b) To enforce complex business rules
c) To compile PL/SQL code
d) To connect to another database
Answers:
9. b) A specific SQL event occurs on a tablesanfoundry+1
10. d) DURINGdevitpl+1
11. b) Once per row affected by the statementsanfoundry+1
12. b) To enforce complex business rulesdevitpl+1
2. Fill‑in‑the‑blanks (with answers)
1.
In Embedded SQL, SQL statements are
processed by a ________ before the host‑language compiler runs.
Answer: preprocessordb-book+1
2.
In JDBC, the ________ interface is used to
execute SQL queries and retrieve results.
Answer: Statement (or PreparedStatement)[sanfoundry]
3.
A PL/SQL ________ returns a value, while a
________ does not.
Answer: function, proceduresimplilearn+1
4.
The keyword ________ is used to define a
trigger in PL/SQL.
Answer: TRIGGERgeeksforgeeks+1
5.
A trigger that fires before an INSERT is
called a ________ trigger.
Answer: BEFOREsanfoundry+1
6.
The pseudo‑records ________ and ________
can be used inside a row‑level trigger to access old and new values.
Answer: :OLD, :NEWdevitpl+1
7.
A ________‑level trigger fires once per
SQL statement, regardless of how many rows are affected.
Answer: statementsanfoundry+1
3. Bloom’s‑taxonomy‑style questions (with
answers)
Level 1–2: Remember / Understand
8.
Knowledge:
List three ways to access SQL from a host programming language.
Answer: Embedded SQL, Dynamic SQL (via APIs such as JDBC/ODBC), calling
stored procedures/functions from the host language.db-book+1
9.
Understand:
Explain the difference between a PL/SQL function and a procedure.
Answer: A function returns a single value and can be used in SQL
expressions (e.g., SELECT), while a procedure performs actions and may have OUT
or IN OUT parameters but does not return a value in the same way.simplilearn+1
Level 3–4: Apply / Analyze
10.
Apply:
Write a PL/SQL function that takes an employee ID and returns the employee’s
salary.
Answer (step‑by‑step):
o Declare
a function get_salary with parameter p_emp_id of type NUMBER.
o Use
RETURN NUMBER to specify the return type.
o In
the IS/AS block, declare a local variable v_salary.
o Use
SELECT salary INTO v_salary FROM employees WHERE emp_id = p_emp_id;.
o Return
v_salary.
o Call
it in SQL: SELECT get_salary(101) FROM dual;.geeksforgeeks+1
11.
Analyze:
Why might you prefer to call a stored procedure from a Java application instead
of writing SQL directly in Java?
Answer: Stored procedures centralize business logic, improve security
(least‑privilege access), reduce network round trips, and make maintenance
easier (change logic in one place).sanfoundry+1
Level 5–6: Evaluate / Create
12.
Evaluate:
Compare the use of triggers versus application‑level code for enforcing a
business rule such as “salary cannot be decreased by more than 10% in a single
update.”
Answer:
o Triggers
enforce the rule at the database level, so all applications (even ad‑hoc tools)
are covered.
o Application
code can be bypassed or duplicated across clients; triggers avoid that but can
make debugging harder and may impact performance if not designed well.devitpl+1
13.
Create:
Design a trigger that logs every update to an EMPLOYEES table into an EMP_LOG
table, recording the old salary, new salary, and timestamp.
Answer outline:
o Create
an EMP_LOG(emp_id, old_sal, new_sal, change_date) table.
o Define
a row‑level AFTER UPDATE trigger on EMPLOYEES.
o Inside
the trigger body, insert into EMP_LOG using :OLD.emp_id, :OLD.salary, :NEW.salary,
and SYSDATE.sanfoundry+1
4. PL/SQL examples with step‑by‑step
working
Example 1: Simple function
sql
CREATE OR REPLACE
FUNCTION get_salary(p_emp_id NUMBER)
RETURN NUMBER
IS
v_salary
NUMBER;
BEGIN
SELECT
salary INTO v_salary
FROM
employees
WHERE
emp_id = p_emp_id;
RETURN
v_salary;
END;
/
Step‑by‑step how it works:
1.
CREATE OR REPLACE FUNCTION
get_salary(p_emp_id NUMBER)
o Defines
a function named get_salary that takes one input parameter p_emp_id of type NUMBER.simplilearn+1
2.
RETURN NUMBER
o Declares
that the function will return a numeric value.[geeksforgeeks]
3.
IS (or AS)
o Starts
the declaration section where local variables are defined.[geeksforgeeks]
4.
v_salary NUMBER;
o Declares
a local variable v_salary to hold the retrieved salary.[geeksforgeeks]
5.
BEGIN ... END;
o The
executable block:
§ SELECT
salary INTO v_salary ... fetches the salary for the given emp_id into v_salary.[geeksforgeeks]
§ RETURN
v_salary; sends the value back to the caller.[geeksforgeeks]
6.
Usage in SQL:
sql
SELECT get_salary(101) FROM
dual;
o The
SQL engine calls the function, passes 101, and displays the returned salary.[geeksforgeeks]
Example 2: Simple procedure
sql
CREATE OR REPLACE
PROCEDURE raise_salary(
p_emp_id IN NUMBER,
p_percent IN NUMBER,
p_new_sal OUT NUMBER
)
IS
BEGIN
UPDATE
employees
SET
salary = salary * (1 + p_percent / 100)
WHERE
emp_id = p_emp_id;
SELECT
salary INTO p_new_sal
FROM
employees
WHERE
emp_id = p_emp_id;
END;
/
Step‑by‑step how it works:
1.
PROCEDURE raise_salary(...)
o Defines
a procedure that takes two IN parameters (p_emp_id, p_percent) and one OUT
parameter p_new_sal.simplilearn+1
2.
UPDATE employees ...
o Increases
the salary by the given percentage for the specified employee.[geeksforgeeks]
3.
SELECT salary INTO p_new_sal ...
o Reads
the updated salary and assigns it to the OUT parameter.[geeksforgeeks]
4.
Calling from PL/SQL block:
DECLARE
v_new_sal
NUMBER;
BEGIN
raise_salary(101,
10, v_new_sal);
DBMS_OUTPUT.PUT_LINE('New
salary: ' || v_new_sal);
END;
o The
procedure modifies the row and returns the new salary via v_new_sal.simplilearn+1
Example 3: Trigger (row‑level audit)
sql
CREATE TABLE
emp_log (
emp_id NUMBER,
old_sal NUMBER,
new_sal NUMBER,
change_date DATE
);
CREATE OR REPLACE
TRIGGER audit_salary_update
AFTER
UPDATE OF salary ON employees
FOR EACH
ROW
BEGIN
INSERT
INTO emp_log (emp_id, old_sal, new_sal, change_date)
VALUES
(:OLD.emp_id, :OLD.salary, :NEW.salary, SYSDATE);
END;
/
Step‑by‑step how it works:
1.
CREATE TABLE emp_log ...
o Creates
a log table to store changes.[devitpl]
2.
CREATE OR REPLACE TRIGGER
audit_salary_update
o Names
the trigger audit_salary_update.sanfoundry+1
3.
AFTER UPDATE OF salary ON employees
o Specifies
that the trigger fires after an UPDATE on the salary column of employees.devitpl+1
4.
FOR EACH ROW
o Makes
it a row‑level trigger; it runs once per updated row.sanfoundry+1
5.
Inside BEGIN ... END;
o INSERT
INTO emp_log ...
§ Uses
:OLD.emp_id, :OLD.salary (values before update) and :NEW.salary (values after
update).devitpl+1
§ SYSDATE
records the timestamp of the change.[devitpl]
6.
Effect:
o Every
time someone updates an employee’s salary, a log entry is created
automatically.simplilearn+1
