Temporary Tables in SQLSERVER

Hi Michell

Temporary tables are a useful tool in SQL Server provided to allow for short term use of data. There are two types of temporary table in SQL Server, local and global.
Local temporary tables are only available to the current connection to the database for the current user and are dropped when the connection is closed. Global temporary tables are available to any connection once created, and are dropped when the last connection using it is closed.

Both types of temporary tables are created in the system database tempdb.

Creating Temporary Tables

Temporary tables can be created like any table in SQL Server with a CREATE TABLE or SELECT..INTO statement. To make the table a local temporary table, you simply prefix the name with a (#). To make the table a global temporary table, prefix it with (##).

-- Create a local temporary table using CREATE TABLE
CREATE TABLE #myTempTable
(
  DummyField1 INT,
  DummyField2 VARCHAR(20)
)

-- Create a local temporary table using SELECT..INTO
SELECT
  age AS DummyField1,
  lastname AS DummyField2
INTO #myTempTable
FROM DummyTable
Both of these samples create a local temporary table named #myTempTable with two fields DummyField1 and DummyField2.

To make these into global temporary tables, just replace (#) with (##)

CREATE TABLE ##myTempTable
(
  DummyField1 INT,
  DummyField2 VARCHAR(20)
)

SELECT
  age AS DummyField1,
  lastname AS DummyField2
INTO ##myTempTable
FROM DummyTable

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