Table Variables Vs Temporary Tables

Feature	Table Variables	Temporary Tables
Scope	Current batch	Current session, nested stored procedures. Global: all sessions.
Usage	UDFs, Stored Procedures, Triggers, Batches.	Stored Procedures, Triggers, Batches.
Creation	DECLARE statement only.	CREATE TABLE statement. SELECT INTO statement.
Table name	Maximum 128 characters.	Maximum 116 characters.
Column data types	Can use user-defined data types. Can use XML collections.	User-defined data types and XML collections must be in tempdb to use.
Collation	String columns inherit collation from current database.	String columns inherit collation from tempdb database.
Indexes	Can only have indexes that are automatically created with PRIMARY KEY & UNIQUE constraints as part of the DECLARE statement.	Indexes can be added after the table has been created.
Constraints	PRIMARY KEY, UNIQUE, NULL, CHECK, but they must be incorporated with the creation of the table in the DECLARE statement. FOREIGN KEY not allowed.	PRIMARY KEY, UNIQUE, NULL, CHECK. Can be part of the CREATE TABLE statement, or can be added after the table has been created. FOREIGN KEY not allowed.
Post-creation DDL (indexes, columns)	Statements are not allowed.	Statements are allowed.
Data insertion	INSERT statement (SQL 2000: cannot use INSERT/EXEC).	INSERT statement, including INSERT/EXEC. SELECT INTO statement.
Insert explicit values into identity columns (SET IDENTITY_INSERT).	The SET IDENTITY_INSERT statement is not supported.	The SET IDENTITY_INSERT statement is supported.
Truncate table	Not allowed.	Allowed.
Destruction	Automatically at the end of the batch.	Explicitly with DROP TABLE statement. Automatically when session ends. (Global: also when other sessions have no statements using table.)
Transactions	Last only for length of update against the table variable. Uses less than temporary tables.	Last for the length of the transaction. Uses more than table variables.
Stored procedure recompilations	Not applicable.	Creating temp table and data inserts cause procedure recompilations.
Rollbacks	Not affected (Data not rolled back).	Affected (Data is rolled back).
Statistics	Optimizer cannot create any statistics on columns, so it treats table variable has having 1 record when creating execution plans.	Optimizer can create statistics on columns. Uses actual row count for generation execution plan.
Pass to stored procedures	SQL 2008 only, with predefined user-defined table type.	Not allowed to pass, but they are still in scope to nested procedures.
Explicitly named objects (indexes, constraints).	Not allowed.	Allowed, but be aware of multi-user issues.
Dynamic SQL	Must declare table variable inside the dynamic SQL.	Can use temporary tables created prior to calling the dynamic sql.

Difference between @@IDENTITY, SCOPE_IDENTITY, IDENT_CURRENT

What SCOPE_IDENTITY is

SCOPE_IDENTITY is:

• SCOPE_IDENTITY returns the last IDENTITY value inserted into an IDENTITY column in the same scope.
• SCOPE_IDENTITY returns the last identity value generated for any table in the current session and the current scope.
• A scope is a module; a Stored Procedure, trigger, function, or batch.
• Thus, two statements are in the same scope if they are in the same Stored Procedure, function, or batch.
• The SCOPE_IDENTITY() function will return the NULL value if the function is invoked before any insert statements into an identity column occur in the scope.

What IDENT_CURRENT is

IDENT_CURRENT is:

• IDENT_CURRENT returns the last identity value generated for a specific table in any session and any scope.
• IDENT_CURRENT is not limited by scope and session; it is limited to a specified table.

What @@IDENTITY is

@@IDENTITY is:

• @@IDENTITY returns the last identity value generated for any table in the current session, across all scopes.
• After an INSERT, SELECT INTO, or bulk copy statement completes, @@IDENTITY contains the last identity value generated by the statement.
• If the statement did not affect any tables with identity columns, @@IDENTITY returns NULL.
• If multiple rows are inserted, generating multiple identity values, @@IDENTITY returns the last identity value generated.
• The @@IDENTITY value does not revert to a previous setting if the INSERT or SELECT INTO statement or bulk copy fails, or if the transaction is rolled back.

Differences

The differences between them are:

• SCOPE_IDENTITY, IDENT_CURRENT, and @@IDENTITY are similar functions in that they return values inserted into IDENTITY columns.
• SCOPE_IDENTITY and @@IDENTITY will return the last identity values generated in any table in the current session. However, SCOPE_IDENTITY returns values inserted only within the current scope; @@IDENTITY is not limited to a specific scope. A scope is a module; a Stored Procedure, trigger, function, or batch.