Table variables and temporary tables are both used to store temporary data in SQL Server, but they have some differences in terms of scope, performance, and usage. Here's a comparison:

Table Variables

1. Declaration: Declared using the DECLARE statement.

   sql

   DECLARE @TempTable TABLE (
       Column1 INT,
       Column2 VARCHAR(50)
   );
   

2. Scope: Limited to the batch, stored procedure, or function in which they are declared. They are automatically dropped when the batch or procedure ends.

3. Transaction Behavior: Not affected by transaction rollbacks. If a transaction is rolled back, the table variable retains its data.

4. Indexing: Limited indexing options. Only primary keys and unique constraints can be applied. No support for non-clustered indexes.

5. Performance: Generally faster for small datasets due to fewer logging operations. However, performance can degrade with larger datasets.

6. Statistics: Limited support for statistics, which can lead to less optimal execution plans.

7. Usage: Suitable for small to moderate-sized datasets and scenarios where the scope is limited to a single batch or procedure.

Temporary Tables

1. Declaration: Created using the CREATE TABLE or SELECT INTO statements with a prefix # (local) or ## (global).

   sql

   CREATE TABLE #TempTable (
       Column1 INT,
       Column2 VARCHAR(50)
   );
   
   -- Or
   SELECT Column1, Column2
   INTO #TempTable
   FROM SourceTable;
   

2. Scope: Local temporary tables (#TempTable) are limited to the session that created them. Global temporary tables (##TempTable) are accessible by all sessions but are dropped when the session that created them ends and no other session is using them.

3. Transaction Behavior: Affected by transaction rollbacks. If a transaction is rolled back, the changes to the temporary table are also rolled back.

4. Indexing: Support for primary keys, unique constraints, and non-clustered indexes. You can create indexes explicitly using the CREATE INDEX statement.

5. Performance: Generally better performance for larger datasets due to support for indexing and statistics. Temporary tables use the tempdb database.

6. Statistics: Full support for statistics, leading to better query optimization.

7. Usage: Suitable for larger datasets and scenarios where temporary data needs to be accessed across multiple batches or sessions.

Summary Table

Here's a quick comparison of key differences:

Both table variables and temporary tables are useful tools, and the choice between them depends on the specific requirements of your task. If you have any specific use cases or need further details, feel free to let me know!