Differences between Temp Tables and Table Variable

Top 15 differences between Temporary Tables and Table Variables in SQL Server:

1. Performance: 

A temporary table works faster if we have a large dataset. 

We can create indexes that can be optimized by the query optimizer.

The table variable works faster if the dataset is small.

Faster because the table variable is stored in memory.

2. Storage: 

The TempDB database houses temporary tables.

Table variables are compact and memory-based.

3. Lifetime: 

Until we remove the table or the session expires, a temporary table is accessible.

However, after the batch or operation is finished, it is immediately erased from the table variable.

4. Indexing: 

We can create indexes on temporary tables.

But we can't create indexes on table variables.

5. Transactions: 

We can easily use temporary tables in transactions.

But we can't use table variables in transactions.

6. Use as Parameter: 

We can use table variables as parameters & can pass in stored procedures.

But we can't use temporary tables as parameters & pass in stored procedures.

7. Memory Usage: 

There is no limit to memory utilization for table variables.

And table variables may consume more memory than temporary tables.

But a temporary table has a limit for memory utilization.

8. Table size: 

Max. size of table variables is 8,000 bytes.

But there is no size limit for temporary tables.

9. Reuse: 

We can reuse temporary tables in multiple sessions & procedures.

But the scope of table variables is a current session or within the procedure only.

10. Table types: 

Table variables are of a single table type, while temporary tables can be created with different types, such as local and global temporary tables.

11. Query optimization: 

SQL Server has a feature to optimize temporary tables through query optimizer. 

But the same feature is not available for table variables.

12. Backup and recovery: 

We can't take backup of temporary tables. And also this is not recoverable.

While table variables are also not recoverable.

But the values of table variables can be saved in a permanent table for further backup and recovery purposes.

13. Scope: 

When we create any temporary tables, the system creates the same in the TempDB database and is visible to all sessions.

But when we create table variables, the system creates this & is available within the scope of the single session or procedure.

14. Table-valued functions: 

Table variables can be used in table-valued functions, while temporary tables cannot.

15. Concurrency: 

Temporary table support locking and can be accessed concurrently by multiple sessions, while table variables are not locked and can only be accessed by a single session at a time.

FAQs:

Q1: What is a temp table?

Ans: A temporary table is one that is established in the tempdb database and survives until the connection that produced it is terminated or the table is expressly discarded.

Q2: What is a table variable?

Ans: The answer is that a table variable, like a temporary table, may contain a result set but is saved in memory and has a specific scope for the batch, stored procedure, or function in which it is defined.

Q3: What are the differences in scope between temp tables and table variables?

Ans: Table variables have a smaller scope and are only accessible within the batch, stored procedure, or function in which they are defined, but temporary tables have a larger scope and may be accessed by numerous connections or sessions.

Q4: What are the performance implications of using temp tables versus table variables?

Ans: The performance of temp tables may be impacted by disc I/O operations, especially for big result sets. Table variables can offer quicker access and higher performance for smaller result sets since they are kept in memory.

Q5: Can temp tables be indexed?

Ans: The answer is yes; indexing temp tables makes it possible to get data quickly and improves query speed. Table variables do not support indexing.

Q6: Can table variables be used in transactions?

Ans: Table variables can be utilized in transactions, hence the answer is yes. Along with other database activities, they can be committed or rolled back and are included in the transaction's scope.

Q7: Which is better for storing big quantities of data, temporary tables or table variables?

Ans: Because they may make use of disc storage, temporary tables are typically better suited for storing huge volumes of data. Table variables work well with smaller result sets or calculations that need intermediary steps.

Q8: Can table variables be used as arguments in stored procedures or functions?

Ans: In order to manipulate and process data inside the parameters of functions and stored procedures, table variables can indeed be supplied as parameters.

Q9: Do temp tables or table variables require explicit cleanup?

Ans: As they continue until expressly discarded or the connection is ended, temporary tables need to be actively cleaned up. However, when a variable in a table exits its scope, it is immediately deallocated.

Q10: Can temp tables or table variables be used in recursive queries?

Ans: Because temporary tables persist between statements, they may be utilized in recursive searches. Table variables cannot be utilized in recursive searches because they are deallocated after the scope.

Q11: Can dynamic SQL queries utilize temporary tables or table variables?

Ans: Yes, dynamic SQL queries may use both temp tables and table variables. However, because of their broader breadth and capacity to persist over many batches of dynamic SQL, temp tables are frequently used in such cases.

Q12: Which uses up more memory: temporary tables or table variables?

Ans: Table variables are maintained in memory, however temporary tables, which are saved in the tempdb database, might use more memory. Therefore, table variables could be a preferable choice if memory utilization is an issue.

Q13: Can temp tables or table variables have constraints or defaults?

Ans: Similar to regular tables, temporary tables can also have defaults, constraints, and other database objects attached to them. However, table variables do not allow for the definition of defaults or restrictions.

Q14: Can complicated data formats like XML or JSON be stored using temp tables or table variables?

Ans: Based on the column definitions specified during their formation, both temporary tables and table variables can hold complicated data formats, such as XML or JSON.

Q15: Can temp tables or table variables be used in parallel query execution?

Ans: Temp tables may be used to execute queries in parallel, improving efficiency when working with big datasets. On the other side, table variables do not enable parallel query execution and could not benefit from it.

Q16: Can recursive stored procedures utilize temporary tables or table variables?

Ans: Since they survive several rounds of operation, temporary tables can be utilized in recursive stored procedures. Table variables cannot be utilized directly in recursive stored procedures because they are deallocated after the scope.

Q17: Can temp tables or table variables be used with table-valued functions?

Ans: Depending on the particular needs of the function and the data being processed, table-valued functions can make use of both temp tables and table variables.

Q18: Can temp tables or table variables be used to store intermediate results in complex queries?

Ans: In complicated searches, interim results can be stored in both temp tables and table variables. The decision is dependent on the size of the result set, the necessity for indexing, and the overall requirements for query performance.

Q19: Can temp tables or table variables be used with cursors?

Ans: You can use cursors with both temporary tables and table variables. Within the context of cursor operations, they can be questioned, altered, and processed.

Q20: Can temp tables or table variables be used in transactional scenarios?

Ans: Transactional situations can make use of both temp tables and table variables. They may facilitate data updates and take part in transactions, preserving the consistency and integrity of the data.