insert ,update ,delete in sql vs trigger procedures with realtime example
ChatGPT said:
ChatGPT
1. Insert, Update, Delete in SQL:
These are basic DML (Data Manipulation Language) commands used to
manipulate data within a database table.
Insert: Adds new records to a table.
o Example:
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INSERT INTO Employees (ID, Name, Position, Salary) VALUES (1, 'John
Doe', 'Developer', 50000);
Update: Modifies existing records in a table.
o Example:
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UPDATE Employees SET Salary = 55000 WHERE ID = 1;
Delete: Removes records from a table.
o Example:
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DELETE FROM Employees WHERE ID = 1;
2. Triggers in SQL:
A trigger is a special kind of stored procedure that automatically executes
when certain events (INSERT, UPDATE, DELETE) occur on a table.
Real-Time Example:
Suppose you want to track changes to employee salaries in a company
database. Every time the salary is updated, you want to log this change in
an AuditLog table.
Create Trigger:
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CREATE TRIGGER SalaryUpdateTrigger
AFTER UPDATE ON Employees
FOR EACH ROW
BEGIN
IF OLD.Salary <> NEW.Salary THEN
INSERT INTO AuditLog (EmployeeID, OldSalary, NewSalary,
ChangeDate)
VALUES (OLD.ID, OLD.Salary, NEW.Salary, NOW());
END IF;
END;
Comparison:
Direct SQL Commands (INSERT, UPDATE, DELETE):
o Manually executed by users or applications.
o Useful for straightforward data manipulation tasks.
Triggers:
o Automatically execute when a specified event happens.
o Useful for automating tasks like logging, auditing, or
maintaining integrity across tables without requiring manual
intervention.
4o
You said:
easy example for students with tables and query with explaination
ChatGPT said:
ChatGPT
Let's consider a simple example involving two tables: Students and
StudentScores.
Tables:
1. Students Table:
Student Ag
Name
ID e
1 John Doe 20
Jane
2 19
Smith
Mike
3 21
Ross
2. StudentScores Table:
ScoreI Student Subje Scor
D ID ct e
1 1 Math 85
2 1 English 78
3 2 Math 90
SQL Commands with Examples:
1. INSERT:
Adding a new student and their score to the tables.
Example Query:
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-- Adding a new student to the Students table
INSERT INTO Students (StudentID, Name, Age) VALUES (4, 'Emily Clark',
22);
-- Adding a new score for the new student
INSERT INTO StudentScores (ScoreID, StudentID, Subject, Score) VALUES
(4, 4, 'Math', 88);
Explanation:
The first query adds a new student named "Emily Clark" to the
Students table.
The second query adds a Math score of 88 for "Emily Clark" to the
StudentScores table.
2. UPDATE:
Modifying the details of an existing student or updating their score.
Example Query:
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-- Update the age of John Doe in the Students table
UPDATE Students SET Age = 21 WHERE StudentID = 1;
-- Update the English score of John Doe
UPDATE StudentScores SET Score = 80 WHERE StudentID = 1 AND Subject
= 'English';
Explanation:
The first query updates John Doe's age to 21 in the Students table.
The second query updates John Doe's English score from 78 to 80 in
the StudentScores table.
3. DELETE:
Removing a student or a specific score from the tables.
Example Query:
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-- Delete Jane Smith from the Students table
DELETE FROM Students WHERE StudentID = 2;
-- Delete the Math score of Mike Ross from the StudentScores table
DELETE FROM StudentScores WHERE StudentID = 3 AND Subject = 'Math';
Explanation:
The first query removes Jane Smith from the Students table.
The second query removes Mike Ross's Math score from the
StudentScores table.
Trigger Example:
Suppose we want to automatically add a record to a ScoreAudit table
whenever a student's score is updated, to track changes.
1. ScoreAudit Table:
AuditI Student Subje OldSco NewSco UpdateTi
D ID ct re re me
Trigger Query:
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CREATE TRIGGER UpdateScoreAudit
AFTER UPDATE ON StudentScores
FOR EACH ROW
BEGIN
IF OLD.Score <> NEW.Score THEN
INSERT INTO ScoreAudit (StudentID, Subject, OldScore, NewScore,
UpdateTime)
VALUES (OLD.StudentID, OLD.Subject, OLD.Score, NEW.Score, NOW());
END IF;
END;
Explanation:
This trigger activates automatically whenever a score is updated in
the StudentScores table.
If the old score is different from the new one, it adds a record to the
ScoreAudit table, logging the change.
4o
You said:
explain sql cammand and triggers wiyh real time examples
ChatGPT said:
ChatGPT
Let's go over SQL commands (INSERT, UPDATE, DELETE) and triggers
with some practical, real-time examples to illustrate how they work in day-
to-day applications.
1. SQL Commands:
These commands are used to manipulate data in the database.
INSERT:
The INSERT command is used to add new records to a table.
Real-Time Example: Imagine an e-commerce website. When a new
customer registers on the site, their details need to be added to the
Customers table.
Example Query:
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INSERT INTO Customers (CustomerID, Name, Email, RegistrationDate)
VALUES (101, 'Alice Johnson', 'alice@example.com', '2024-10-17');
Explanation: This query adds a new customer, Alice Johnson, to the
Customers table.
UPDATE:
The UPDATE command is used to modify existing records.
Real-Time Example: On the same e-commerce website, if a customer
wants to change their delivery address, the system needs to update this
information.
Example Query:
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UPDATE Customers
SET Address = '123 New Street, Springfield'
WHERE CustomerID = 101;
Explanation: This query updates the address of the customer with
CustomerID = 101 to the new address.
DELETE:
The DELETE command is used to remove records from a table.
Real-Time Example: If a customer deletes their account, their data can
be removed from the database.
Example Query:
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DELETE FROM Customers
WHERE CustomerID = 101;
Explanation: This query deletes the record of the customer with
CustomerID = 101.
2. Triggers in SQL:
A trigger is a piece of code that automatically executes when a specified
event occurs on a table, such as an INSERT, UPDATE, or DELETE action.
Real-Time Example with Trigger:
Let's say we have a BankAccounts table that tracks user accounts and
another table called AccountAudit which keeps a log of any changes
made to the balance of an account.
1. BankAccounts Table:
AccountI AccountHol Balanc
D der e
201 John Doe 5000
2. AccountAudit Table:
AuditI AccountI OldBalan NewBalan ChangeDa
D D ce ce te
Trigger Query:
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CREATE TRIGGER BalanceChangeAudit
AFTER UPDATE ON BankAccounts
FOR EACH ROW
BEGIN
IF OLD.Balance <> NEW.Balance THEN
INSERT INTO AccountAudit (AccountID, OldBalance, NewBalance,
ChangeDate)
VALUES (OLD.AccountID, OLD.Balance, NEW.Balance, NOW());
END IF;
END;
Explanation:
This trigger is set to activate after any update to the
BankAccounts table.
When an account’s balance is updated, the trigger checks if the
OLD.Balance (balance before the update) is different from the
NEW.Balance (balance after the update).
If the balance has changed, a record is inserted into the
AccountAudit table, logging the AccountID, OldBalance,
NewBalance, and ChangeDate.
How It Works in Real Life: Suppose John Doe withdraws $1000, and the
BankAccounts table is updated:
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UPDATE BankAccounts
SET Balance = 4000
WHERE AccountID = 201;
Effect of the Trigger: The trigger will automatically add a new record to
the AccountAudit table:
AuditI AccountI OldBalan NewBalan
ChangeDate
D D ce ce
2024-10-17
1 201 5000 4000
10:30:00
Summary:
SQL Commands like INSERT, UPDATE, and DELETE are used to add,
modify, or remove data manually.
Triggers automate tasks, such as logging changes or maintaining
data integrity, by executing specific actions automatically when
certain conditions are met.
4o
You said:
to take real time example with tables and querys
ChatGPT said:
ChatGPT
Let's create a real-time scenario involving a hotel booking system, with
tables and SQL queries to demonstrate INSERT, UPDATE, DELETE
commands, and a trigger.
Scenario: Hotel Booking System
The hotel booking system manages information about customers, room
bookings, and payment transactions.
Tables:
1. Customers Table:
Customer PhoneNum
Name Email
ID ber
Alice alice@example.c 123-456-
1
Johnson om 7890
bob@example.co 987-654-
2 Bob Smith
m 3210
2. Bookings Table:
Booking Customer RoomNum CheckInD CheckOutD
Status
ID ID ber ate ate
Confirme
101 1 203 2024-10-20 2024-10-22
d
Confirme
102 2 305 2024-10-21 2024-10-23
d
3. PaymentTransactions Table:
Transactio Booking Amou PaymentD PaymentSta
nID ID nt ate tus
1001 101 200 2024-10-15 Completed
SQL Commands with Real-Time Examples:
1. INSERT: Adding a New Booking
When a new customer makes a booking, their information is added to the
Customers and Bookings tables.
Example Query:
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-- Add a new customer to the Customers table
INSERT INTO Customers (CustomerID, Name, Email, PhoneNumber)
VALUES (3, 'Charlie Brown', 'charlie@example.com', '555-123-4567');
-- Create a new booking for the customer
INSERT INTO Bookings (BookingID, CustomerID, RoomNumber,
CheckInDate, CheckOutDate, Status)
VALUES (103, 3, 401, '2024-10-25', '2024-10-27', 'Confirmed');
Explanation:
The first query adds a new customer, Charlie Brown, to the
Customers table.
The second query creates a booking for Charlie in room 401.
2. UPDATE: Modifying a Booking
If a customer wants to extend their stay, we can update the
CheckOutDate for their booking.
Example Query:
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-- Update the checkout date for Alice's booking
UPDATE Bookings
SET CheckOutDate = '2024-10-24'
WHERE BookingID = 101;
Explanation: This query updates the checkout date for Alice's booking
from October 22 to October 24.
3. DELETE: Cancelling a Booking
If a customer cancels their booking, we can remove the booking from the
Bookings table.
Example Query:
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-- Delete Bob's booking
DELETE FROM Bookings
WHERE BookingID = 102;
Explanation: This query removes Bob's booking from the Bookings
table.
Trigger Example: Automatically Log Payment Transactions
To track any updates to the PaymentTransactions table, we can set up a
trigger that logs every time a payment is marked as completed.
1. PaymentLog Table:
LogI Transactio Booking Amou LogDa
D nID ID nt te
Trigger Query:
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CREATE TRIGGER PaymentCompletionLog
AFTER UPDATE ON PaymentTransactions
FOR EACH ROW
BEGIN
IF OLD.PaymentStatus <> NEW.PaymentStatus AND NEW.PaymentStatus
= 'Completed' THEN
INSERT INTO PaymentLog (TransactionID, BookingID, Amount, LogDate)
VALUES (NEW.TransactionID, NEW.BookingID, NEW.Amount, NOW());
END IF;
END;
Explanation:
This trigger automatically executes whenever a record is updated in
the PaymentTransactions table.
It checks if the PaymentStatus has changed to "Completed". If so, it
logs this information in the PaymentLog table.
Real-Time Use: Let's say a customer pays for their booking, and the
system updates the payment status:
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UPDATE PaymentTransactions
SET PaymentStatus = 'Completed'
WHERE TransactionID = 1002;
Effect of the Trigger: If the payment status is updated to "Completed,"
the following record will be automatically inserted into the PaymentLog:
LogI Transactio Booking Amou
LogDate
D nID ID nt
2024-10-17
1 1002 103 250
11:45:00
Summary:
INSERT, UPDATE, and DELETE commands help in adding,
modifying, and removing records manually.
Triggers automate processes, such as logging payment
completions, and enhance system efficiency by automatically
handling repetitive tasks.
4o
You said:
how to write the procedures in sql
ChatGPT said:
ChatGPT
In SQL, a stored procedure is a set of SQL statements that you can save
and reuse. Stored procedures allow you to encapsulate logic, making it
easier to manage and reuse code. Let's go through how to write a
procedure with a real-time example.
General Syntax for Stored Procedures:
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CREATE PROCEDURE procedure_name (parameters)
BEGIN
-- SQL statements
END;
Real-Time Example: Hotel Booking System
Suppose we want to create a stored procedure that adds a new booking
and updates the availability of a room.
1. Bookings Table:
Booking Customer RoomNumb CheckInDa CheckOutD Statu
ID ID er te ate s
2. Rooms Table:
RoomNumb Pric Availabili
Type
er e ty
101 Deluxe 150 Available
Standar
102 100 Available
d
Stored Procedure to Add a New Booking:
This procedure will:
Insert a new booking into the Bookings table.
Update the room status to "Unavailable" in the Rooms table after
the booking is confirmed.
Procedure Code:
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CREATE PROCEDURE AddNewBooking (
IN customerID INT,
IN roomNumber INT,
IN checkIn DATE,
IN checkOut DATE
BEGIN
-- Step 1: Insert a new booking
INSERT INTO Bookings (CustomerID, RoomNumber, CheckInDate,
CheckOutDate, Status)
VALUES (customerID, roomNumber, checkIn, checkOut, 'Confirmed');
-- Step 2: Update the room availability
UPDATE Rooms
SET Availability = 'Unavailable'
WHERE RoomNumber = roomNumber;
END;
Explanation:
Parameters: customerID, roomNumber, checkIn, and checkOut are
input parameters.
Step 1: Inserts a new booking record with the given information,
setting the status as "Confirmed".
Step 2: Updates the Rooms table, changing the availability of the
booked room to "Unavailable".
Calling the Stored Procedure:
To use the procedure, you call it and provide the required parameters.
Example Query:
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CALL AddNewBooking(3, 101, '2024-10-25', '2024-10-27');
Explanation: This command calls the AddNewBooking procedure to:
Add a new booking for CustomerID = 3 in RoomNumber = 101 from
October 25 to October 27.
Mark RoomNumber 101 as "Unavailable" in the Rooms table.
Another Example: Procedure for Cancelling a Booking
If a customer wants to cancel a booking, we might also want to update
the booking status and make the room available again.
Procedure Code:
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CREATE PROCEDURE CancelBooking (
IN bookingID INT
BEGIN
-- Step 1: Update the booking status to 'Cancelled'
UPDATE Bookings
SET Status = 'Cancelled'
WHERE BookingID = bookingID;
-- Step 2: Retrieve the RoomNumber associated with the booking
DECLARE roomNum INT;
SELECT RoomNumber INTO roomNum FROM Bookings WHERE
BookingID = bookingID;
-- Step 3: Update the room availability
UPDATE Rooms
SET Availability = 'Available'
WHERE RoomNumber = roomNum;
END;
Explanation:
This procedure cancels a booking by setting its status to
"Cancelled".
It retrieves the RoomNumber from the Bookings table and updates
the room availability to "Available" in the Rooms table.
Calling the Procedure:
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CALL CancelBooking(101);
Explanation: This call cancels the booking with BookingID = 101 and
marks the room as "Available".
Summary:
Stored procedures help encapsulate complex operations, reduce
repetitive coding, and improve maintainability.
Parameters can be used to pass information to procedures (IN,
OUT, INOUT).
Procedures are particularly useful in real-world scenarios like
booking systems, where multiple steps need to be executed
together (e.g., creating a booking and updating room availability).
4o
