SQL Server Temp tables - SQL Local and Global Temporary tables

The temporary or temp table in SQL Server can be created at the run-time and perform all the operations that a regular table can do. There are two types of Temporary Tables in SQL Server, and they are Local Temporary Tables and Global Temporary Tables. Let us see how to work with both Local and Global Temp tables in SQL Server. The following list shows you where we can use the SQL temp tables:

When we are working with the complex SQL Server joins.
Temp tables are useful to replace the costly cursors. We can use this temp table to store the result set data and manipulate the data from the temp table.
We can use this SQL temp table when we are doing a large number of row manipulation in stored procedures. Remember, If we create a temp table inside a stored procedure, it applicable to that SP only. It means you can not call the temp table outside the stored procedure.

Local Temp Table in SQL Server

The name of the SQL Local temporary table starts with the hash (“#”) symbol and stored in the tempdb. SQL Local temporary tables are available only in the current connection. If the user disconnects from current instances or closes the query window, then SQL Local temporary table deletes automatically.

Local Temp Table in SQL Server Syntax

The syntax behind the Sql Server local temporary tables

CREATE TABLE #[Local Temp Table]
(
    Column_Name1 Data_Type(Size) [NULL | NOT NULL],
    Column_Name2 Data_Type(Size) [NULL | NOT NULL],
     …
    Column_NameN Data_Type(Size) [NULL | NOT NULL]
);

Here, Table Name of a SQL local temporary table should start with #. Remember, Please provide a unique name. If you gave the existing table name, it will throw an error

Let us create a SQL local temporary table called LocalTemp.

-- Creating Local Temp Table in SQL Server 
CREATE TABLE #LocalTemp
(
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[FirstName] [nvarchar](255) NULL,
	[LastName] [nvarchar](255) NULL,
	[Occupation] [nvarchar](255) NULL,
	[YearlyIncome] [float] NULL,
	[Sales] [float] NULL
)

We declared 6 Columns in our local temp table. Here, Our first column is ID of Integer data type, and it won’t allow NULL values. We also defined this SQL Server column as Identity starts with 1 and incremented by 1. Please refresh the object explorer to see the Newly created Local Temporary table in SQL Server

Insert Data into Local Temp Table in SQL Server

Let me insert a few random, or sample records into the SQL local temporary table that we created inside the tempdb using the INSERT Statement.

-- Inserting Values into Local SQL Temp Table
INSERT INTO #LocalTemp (
	    [FirstName], [LastName], [Occupation], [YearlyIncome], [Sales])
VALUES ('Tutorial', 'Gateway', 'Education', 10000, 200)
      ,('Imran', 'Khan', 'Skilled Professional', 15900, 100)
      ,('Doe', 'Lara', 'Management', 15000, 60)
      ,('Ramesh', 'Kumar', 'Professional', 65000, 630)

We successfully inserted 4 random records into the #Local Temp table.

Select Data from Local Temp Table

Let me use the SELECT Statement to select the records present in the local temp table in Sql Server.

-- Selecting Values From Local SQL Temp Table
SELECT [FirstName], 
       [LastName], 
       [Occupation], 
       [YearlyIncome], 
       [Sales] 
FROM #LocalTemp

Until now, you might wonder why I am writing the Create, Insert, and Select statements in one query window?. Because SQL local temporary tables will last up to a single session, and if you try to call this table from a new query window, then it will throw an error. For example, let me call the #LocalTemp table from a new query window

As you can see, it is throwing an error stating that, Invalid Object name #LocalTemp. Now, let me close all the existing query windows, and refresh the tempdb from Object Explorer

From the above screenshot, you can see that it does not contain our #LocalTemp table.

Global Temp Table in SQL Server

The name of the SQL Global temporary table starts with the double hash (“##”) symbol and stored in the tempdb. Global temp tables in SQL Server are like permanent tables, and they are available to all the users in that instance. If all the user disconnects from their session, the SQL global temp tables will automatically delete.

Global Temp Table in SQL Server Syntax

The syntax behind the Global temporary tables in Sql Server

CREATE TABLE ##[Global Temp Table Name]
(
    Column_Name1 Data_Type(Size) [NULL | NOT NULL],
    Column_Name2 Data_Type(Size) [NULL | NOT NULL],
     …
    Column_NameN Data_Type(Size) [NULL | NOT NULL]
);

The SQL global temporary table name should start with ##. Please provide a unique otherwise, it throws an error. Let us create a SQL global temporary table called GlobalTemp.

-- Creating Global Temp Table in SQL Server 
CREATE TABLE ##GlobalTemp
(
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[FirstName] [nvarchar](255) NULL,
	[LastName] [nvarchar](255) NULL,
	[Education] [nvarchar](255) NULL,
	[Occupation] [nvarchar](255) NULL,
	[YearlyIncome] [float] NULL,
	[Sales] [float] NULL
)

We declared 7 Columns for this temp table. See the Newly created Global Temporary table in Sql Server.

Insert Data into Global Temp Table in SQL Server

Let me insert a few samples or random records into the global temp table in Sql Server that we created inside the tempdb using the INSERT Statement.

-- Inserting Values into Global SQL Temp Table
INSERT INTO ##GlobalTemp (
	    [FirstName], [LastName], [Education], [Occupation], [YearlyIncome], [Sales])
VALUES ('Tutorial', 'Gateway', 'Masters Degree', 'Teaching', 12000, 200)
      ,('Imran', 'Khan', 'Bachelors', 'Skilled Professional', 13900, 100)
      ,('Doe', 'Lara', 'Degree', 'Management', 25000, 60)
      ,('Ramesh', 'Kumar', 'Bachelors', 'Professional', 35400, 630)

Select from Global Temp Table

Here, we successfully inserted 4 random records into the ##GlobalTemp table. Let me use the SELECT Statement to select the records present in that global temp table in Sql Server.

-- Selecting Values From Global SQL Temp Table
SELECT [ID],
       [FirstName], 
       [LastName], 
       [Education], 
       [Occupation],
       [YearlyIncome], 
       [Sales] 
FROM ##GlobalTemp

Next, let me call the ##Global Temp table in SQL from a new query window

The Temp table is displaying the records, rather than throwing an error. Now, let me close all the existing query windows, and refresh the tempdb from Object Explorer

Now you can see that there are no temp tables in tempdb database. Please refer to cursors and stored procedures articles.