Can I loop through a table variable in T-SQL?

Set-based alternatives & performance boosters

Use of set-based solutions over cursors

Even though cursors may seem charming, the set-based approach is the Usain Bolt of SQL. It can perform aggregation tasks faster, leaving cursors in the dust:

-- Example of a set-based approach that eliminates the need for looping
SELECT SUM(salary) FROM Employees WHERE DepartmentID = @DepartmentID;
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Role of identity column

An identity column is a must-have for any table variable that requires looping. It's like the key to your apartment—you simply can't enter without it:

-- Assuming @MyTable has an identity column
DECLARE @CurrentRow INT = 1, @TotalRows INT;
-- Getting the total number of rows. It's like checking how many pizzas we got!
SELECT @TotalRows = COUNT(*) FROM @MyTable;

WHILE @CurrentRow <= @TotalRows
BEGIN
    -- Keep fetching till you get'em all!
    SELECT @ID, @Name FROM @MyTable WHERE ID = @CurrentRow;
    SET @CurrentRow = @CurrentRow + 1;
END;
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Count rows with @@ROWCOUNT

Ensure you count your eggs before you start cooking! In SQL terms, capture the number of affected rows using @@ROWCOUNT after working on your table variable:

-- Somewhat like an in-built SQL fitbit tracker for your rows.
INSERT INTO @MyTable SELECT ID, Name FROM Employees;
SET @TotalRows = @@ROWCOUNT;
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Use ROW_NUMBER when identity column is absent

No identity column? No problem! Use ROW_NUMBER() to divide and conquer:

-- This is your plan B when identity columns ditch you.
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS RowNum, * INTO #TempTable FROM @MyTable;
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Make use of countdown approach

Time for some SQL aerobics! After a healthy climb up the rows, it's time to count down:

SET @RowsToProcess = @TotalRows;

WHILE @RowsToProcess > 0
BEGIN
    --  Reverse crunches for rows! Feel the burn!
    SELECT @ID, @Name FROM @MyTable WHERE ID = @RowsToProcess;
    SET @RowsToProcess = @RowsToProcess - 1;
END;
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Use CONCAT for some fun while looping

When SQL gets tedious, have some fun with the CONCAT function and grace your log outputs with it:

--  It's like a step counter at work. It's more fun when you keep track!
PRINT CONCAT('Processing row ', @CurrentRow, ' out of ', @TotalRows);
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Make the jump from iterations to set-based approach

Replace iterative actions with set-based ones. Ask your peers or StackOverflow pals (shhh!) when you need help translating tricky loops into set-based operations.

Use case scenarios & edge sharpening tips

Iterate smarter and safer

Knowing the ins and outs of loop control can help you avoid painful SQL miscalculations. It's similar to stepping on LEGO—experience tells you to tread with caution.

Say NO to RBAR (Row-By-Agonizing-Row)

See that RBAR pattern coming? Dodge it and switch to a set-based approach. Be smarter and cut the SQL red wire of RBAR!

Welcome community criticism and aid

Can't convert that loop into a set-based operation? Don't worry, ask for help. It's like multiplayer mode in video games, you get to finish levels faster.

Keep an eye on performance

Remember, performance is the king in the SQL world. Be it a cursor, a loop, or a set-based operation, choose wisely!

Find the right place for loops

Loops can seem annoying. But they are just misunderstood creatures. You can't avoid them completely, especially when you need to perform complex calculations!