SQL Server provides us with alternatives to the traditional “for” loop which offers more efficient and optimized ways to iterate over the data sets and perform iterative operations. These alternatives for “for” loops enable an efficient iteration and data manipulation.
Let us discuss about some important SQL server “for” loop alternatives. We will talk about the “while” loop which enables the iterative operations. We will also discuss about the “tally” table which is a powerful mechanism to generate sequential numbers. After understanding the strengths and use cases of each alternative, the readers can decide the appropriate method to use. These alternatives not only enhance the code readability and maintainability but also improve performance and efficiency in the SQL Server data manipulation.
Create a Table for Demonstration
Let us create a sample table to better illustrate the different SQL Server “for” loop alternatives. Let’s first create a table called “Employees” with columns such as “EmID”, “Name”, and “Salary”.
EmID INT,
Name VARCHAR(50),
Salary DECIMAL(10, 2)
);
GO
INSERT INTO Employees (EmID, Name, Salary)
VALUES
(1, 'Raj Misha', 50000.00),
(2, 'Amit Nath', 60000.00),
(3, 'Sneha Paul', 55000.00),
(4, 'Priya Dutta', 48000.00),
(5, 'Anil Kumar', 52000.00),
(6, 'Meera Kumari', 57000.00);
Output:
1 Raj Misha 50000.00
2 Amit Nath 60000.00
3 Sneha Paul 55000.00
4 Priya Dutta 48000.00
5 Anil Kumar 52000.00
6 Meera Kumari 57000.00
Some SQL Server FOR Loop Alternatives
1. WHILE Loop in the SQL Server
A very popular alternative to “for” loop in the SQL Server is the WHILE loop. We can effectively iterate over a result set or perform iterative operations on a set of data using the WHILE loop. For example, we want to raise each employee’s pay by 10% in the table named “Employees”. We can perform this using a WHILE loop.
DECLARE @TotalRows INT = (SELECT COUNT(*) FROM Employees);
WHILE @Counter <= @TotalRows
BEGIN
DECLARE @EmID INT;
DECLARE @Salary DECIMAL(10, 2);
-- Retrieve EmID and Salary for the current row
SELECT @EmID = EmID, @Salary = Salary
FROM Employees
WHERE EmID = @Counter;
-- Increase the salary by 10%
SET @Salary = @Salary * 1.1;
-- Update the salary for the current employee
UPDATE Employees
SET Salary = @Salary
WHERE EmID = @EmID;
-- Print the updated salary
PRINT 'Updated salary for EmID ' + CAST(@EmID AS VARCHAR) + ': ' + CAST (@Salary AS VARCHAR);
-- Increment the counter
SET @Counter = @Counter + 1;
END
Output:
Updated salary for EmID 1: 60500.00
Updated salary for EmID 2: 72600.00
Updated salary for EmID 3: 66550.00
** many more outputs **
Updated salary for EmID 4: 58080.00
Updated salary for EmID 5: 62920.00
Updated salary for EmID 6: 68970.00
Here, it iterates over the rows in the “Employees” table and updates the salary by 10% and continues until all rows are updated.
2. Using the Tally Table in the SQL Server
The “tally” table, sometimes referred to as the “numbers” table, is an effective method that includes generating a list of consecutive numbers into a table. The creation of iterative sequences or the execution of set-based operations may then be done using this table. Using the tally table method, we can eliminate the need for “for” loops in the SQL Server. To get the names of all employees, we can perform this using a “tally” table.
CREATE TABLE Tally (Number INT);
DECLARE @MaxNumber INT = (SELECT MAX (EmID) FROM Employees);
WITH K AS (
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS No
FROM sys.all_columns AS AC1
CROSS JOIN sys.all_columns AS AC2
)
INSERT INTO Tally (Number)
SELECT No
FROM K
WHERE No <= @MaxNumber;
-- Retrieve employee names using the tally table
SELECT E.Name
FROM Employees AS E
JOIN Tally AS T ON E.EmID = T.Number;
--At last, Drop the tally table
DROP TABLE Tally;
Output:
1 Raj Misha
2 Amit Nath
3 Sneha Paul
4 Priya Dutta
5 Anil Kumar
6 Meera Kumari
Here, we create a “tally” table with a single column named “Number” in the T-SQL query. By determining the maximum number of employees from the “EmID” column in the “Employees” table, we then create a sequence of numbers from 1 to the maximum using the variable “K”. This variable “K” assigns a new value to each row using the “ROW_NUMBER ()” function. After that, we insert then these generated numbers into the “tally” table, limiting the insertion to numbers that are less than or equal to the maximum employee number. Lastly, we join the “Employees” table with the “tally” table based on the equality of the “EmID” and “Number” columns.
Conclusion
SQL Server provides several alternatives to the “for” loop and offers more efficient and optimized ways to iterate over the data sets and perform iterative operations. The WHILE loop allows us to execute the code repeatedly based on a specific condition, providing flexibility for iterative tasks. Moreover, the use of a tally table eliminates the need for loops. Using these alternatives methods, we can improve our SQL Server skills and achieve a more efficient data manipulation.
