5.1 INSERT, UPDATE, DELETE statements

 

5.1 INSERT, UPDATE, DELETE Statements

5.1.1 INSERT Statement

The INSERT statement is used to add new records to a table.

Syntax:

INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);

Example: Consider a table named Employees with columns EmployeeID, FirstName, and LastName.

-- Inserting a new employee
INSERT INTO Employees (EmployeeID, FirstName, LastName)
VALUES (1, 'John', 'Doe');

Query Output:

EmployeeID	FirstName	LastName
1	John	Doe

5.1.2 UPDATE Statement

The UPDATE statement is used to modify existing records in a table.

Syntax:

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Example: Continuing with the Employees table, let's update John Doe's last name.

-- Updating the last name of employee with ID 1
UPDATE Employees
SET LastName = 'Smith'
WHERE EmployeeID = 1;

Query Output:

EmployeeID	FirstName	LastName
1	John	Smith

5.1.3 DELETE Statement

The DELETE statement is used to remove records from a table.

Syntax:

DELETE FROM table_name WHERE condition;

Example: Removing the employee with ID 1 from the Employees table.

-- Deleting the employee with ID 1
DELETE FROM Employees WHERE EmployeeID = 1;

Query Output:

EmployeeID	FirstName	LastName
(No rows)	(No rows)	(No rows)

This table would indicate that there are no rows left after the DELETE operation.

Conclusion

Understanding how to use INSERT, UPDATE, and DELETE statements is essential for manipulating data within SQL Server tables. Always be cautious when using DELETE to avoid unintentional data loss.