How to Update a Column in a Table in SQL Server

In the database management area, updating columns in a table is a normal query and it is important software that ensures the accuracy and integrity of data. Whether we are making spelling corrections, editing or altering existing information, or being attentive to changing requirements, carrying out changes accurately is essential.

In this article, we will learn about Updating a Column in a Table with multiple examples and their best practices in detail.

What is an UPDATE Statement in SQL Server

In SQL Server, the UPDATE statement is the tool that allows the changing of the existing records in a table:

UPDATE table_name
SET column1 = value1, column2 = value2, ...an 

Explanation:

• UPDATE table_name: Specifies the name of the table that you want to update.
  
• SET column1 = value1, column2 = value2, ...: Assigns new values to the specified columns. Each column is followed by an equal sign (=) and the new value that you want to set. You can update multiple columns at once by separating them with commas.
  ,
• WHERE condition: Specifies the condition that determines which records to update. If omitted, all records in the table will be updated. The WHERE clause is optional but highly recommended to avoid unintended updates.

Example of Updating a Column in a Table

CREATE TABLE employees (
    emp_id INT PRIMARY KEY,
    emp_name VARCHAR(50),
    emp_department VARCHAR(50),
    emp_salary DECIMAL(10, 2)
);

INSERT INTO employees (emp_id, emp_name, emp_department, emp_salary)
VALUES
    (1, 'John Smith', 'Marketing', 50000),
    (2, 'Alice Wang', 'Sales', 55000),
    (3, 'Emma Brown', 'HR', 48000);

Output:

emp_id | emp_name    | emp_department | emp_salary
-------|-------------|----------------|-----------
1      | John Smith  | Marketing      | 50000
2      | Alice Wang  | Sales          | 55000
3      | Emma Brown  | HR             | 48000

Example 1: Updating an Employee's Salary

Suppose John Smith's salary needs to be increased to $52000:

UPDATE employees
SET emp_salary = 52000
WHERE emp_name = 'John Smith';

Output:

emp_id | emp_name    | emp_department | emp_salary
-------|-------------|----------------|-----------
1      | John Smith  | Marketing      | 52000
2      | Alice Wang  | Sales          | 55000
3      | Emma Brown  | HR             | 48000

Explanation:

• The UPDATE statement modifies existing records in the employees table.
• SET emp_salary = 52000 updates the emp_salary column for the specified employee (John Smith) to the new value of $52000.
• WHERE emp_name = 'John Smith' specifies the condition for updating only the record where the employee's name is 'John Smith'.

Example 2: Changing an Employee's Department

Suppose Emma Brown is transferred from HR to Finance department:

UPDATE employees
SET emp_department = 'Finance'
WHERE emp_name = 'Emma Brown';

Output:

emp_id | emp_name    | emp_department | emp_salary
-------|-------------|----------------|-----------
1      | John Smith  | Marketing      | 52000
2      | Alice Wang  | Sales          | 55000
3      | Emma Brown  | Finance        | 48000

Explanation:

• Similar to the previous example, this UPDATE statement modifies the emp_department column for the specified employee (Emma Brown) to the new value of 'Finance'.
• The condition WHERE emp_name = 'Emma Brown' ensures that only Emma Brown's record is updated.

Example 3: Incrementing Salary for All Employees

Suppose there's a company-wide salary increment of 5%:

UPDATE employees
SET emp_salary = emp_salary * 1.05;

Output:

emp_id | emp_name    | emp_department | emp_salary
-------|-------------|----------------|-----------
1      | John Smith  | Marketing      | 54600
2      | Alice Wang  | Sales          | 57750
3      | Emma Brown  | Finance        | 50400

Explanation:

• Here, emp_salary * 1.05 calculates the new salary by increasing the existing salary by 5% for all employees.
• Since no WHERE clause is specified, this update affects all records in the employees table.
• After executing the update, the employees table will reflect the incremented salaries for all employees.

Best Practices for Updating Columns

Adhering to best practices not only ensures the accuracy of updates but also enhances the efficiency of database operations:

• Use Explicit Criteria: Indicate criteria for selection of records which needs to be updated. Indeterminacy in classification criteria may cause contradictory amendments.
  
• Transaction Management: Enclose your updates statements within transaction, particularly when updating multiple tables concurrently. Transactions apply the ACID properties are Atomicity, Consistency, Isolation, and Durability on database operations.
  
• Backup Data: Back up data before carrying out updates to be safe. This risk mitigation measure minimizes the possibility of daunting alterations.
  
• Avoid Mass Updates: Keep in mind that updating a big amount of records may some risk. Database updates frequently affect performance of data in addition to concurrency. Consider batching the updates or doing them outside the strong traffic hours when possible.

Conclusion

Changes in database columns is a matter of database management and implies the possibility of changing data and making data flexible. Understanding the SQL UPDATE statement and its syntax, as well as practical examples, can make you to perform changes to existing table records in a simple manner. Among the best practices are establishment of criteria for explicit criteria, transaction management, and backup, which enriches the integrity and efficiency of the update operation and promotes a robust database management.