How do you create a temporary table in SQL?

A temporary table in SQL is a table that exists only for the duration of a session or a specific transaction. It’s mainly used to store intermediate results or perform complex calculations before getting the final output.

In SQL Server, you can create a temporary table using the # symbol:

CREATE TABLE #TempEmployees (
    EmployeeID INT,
    EmployeeName VARCHAR(100),
    Department VARCHAR(50)
);

Then, you can insert and query data just like a normal table:

INSERT INTO #TempEmployees VALUES (1, 'John', 'HR');
SELECT * FROM #TempEmployees;

Once the session ends (or connection is closed), the temporary table is automatically dropped — you don’t need to delete it manually.

There are two types of temporary tables:

1. Local Temporary Table (#Temp) – visible only to the current session.
2. Global Temporary Table (##Temp) – visible to all sessions until the last session using it is closed.

In MySQL, you can use the TEMPORARY keyword:

CREATE TEMPORARY TABLE TempEmployees (
    EmployeeID INT,
    EmployeeName VARCHAR(100),
    Department VARCHAR(50)
);

A common challenge I faced was forgetting to add proper indexing or cleaning up large temporary data, which sometimes slowed down queries. To handle this, I make sure to create only the required columns and drop the temp tables manually if they hold heavy data using:

DROP TABLE IF EXISTS #TempEmployees;

In short, temporary tables are extremely useful for staging intermediate results, improving query readability, and boosting performance during complex SQL operations.