Define a Temp Table

A temporary table, often referred to as a "temp table," is a type of table in SQL that is used to store data temporarily during the execution of a query or a series of queries. Temp tables are particularly useful for intermediate storage of data that is needed only for the duration of a session or transaction. Here are some key points about temp tables:

Characteristics of Temp Tables

1. Scope and Lifespan:

   • Local Temporary Tables: These are prefixed with a single hash symbol (#). They are visible only within the session that created them and are automatically dropped when the session ends.
   • Global Temporary Tables: These are prefixed with a double hash symbol (##). They are visible to all sessions and are dropped when the session that created them ends and the last active session referencing them is closed.

2. Creation and Usage:

   • Temp tables can be created using the CREATE TABLE statement with the appropriate prefix (# or ##).
   • They can be populated using INSERT INTO or SELECT INTO statements.
   • Temp tables support typical SQL operations such as SELECT, INSERT, UPDATE, and DELETE.

3. Performance:

   • Temp tables are stored in the tempdb database, which is optimized for temporary storage and operations.
   • They can improve performance by reducing the need for repeated complex calculations or data transformations.
   • Temp tables can have indexes, constraints, and statistics, similar to permanent tables, which can further enhance performance for certain operations.

4. Use Cases:

   • Intermediate Storage: Useful for storing intermediate results during complex data transformations or ETL (Extract, Transform, Load) processes.
   • Query Simplification: Breaking down complex queries into simpler steps by storing intermediate results in temp tables.
   • Data Isolation: Ensuring that temporary data used in one session does not interfere with data in other sessions.

Example of Creating and Using a Temp Table

-- Create a local temporary table
CREATE TABLE #TempStudents (
    StudentID INT PRIMARY KEY,
    FirstName NVARCHAR(50),
    LastName NVARCHAR(50),
    Age INT
);

-- Insert data into the temp table
INSERT INTO #TempStudents (StudentID, FirstName, LastName, Age)
VALUES (1, 'John', 'Doe', 20);

-- Select data from the temp table
SELECT * FROM #TempStudents;

-- Drop the temp table
DROP TABLE #TempStudents;

Advantages and Disadvantages

**Adv...