SQL: Create a temporary table

Temporary tables are a great way of working on complex data requests. They are easy to create and they delete themselves after every session, so you do not have to worry about creating a big mess with a bunch of tables you need to go clean up later.

In this tutorial, I am going to use a real world example from my work in Verizon’s Cyber Security Department. This is a simplified version of ask, and I am using completely made up data. There is no data from Verizon on my website every. I simply discuss use cases to make learning analytics more grounded in the real world

Below is a list of dates, PhoneNum: phone numbers called about, and the CallerNum: the number the person is calling from. While there are many legitimate reasons for someone to call customer support from another number (I drop and break my phone so I borrow my co-workers phone and call customer support to request a replacement), a number that calls in repeatedly about many different numbers is a red flag of someone that could be a fraudster.

If you want to play along, you can download the data set here:

I am using MySql in this example as my database, but I will include the code for SQL Server, Teradata, and Oracle platforms as well.

So the ask is find CallerNum that is calling about many different PhoneNum

While I am sure you can make a complex subquery to do this job, but I’m going to show you how to use temporary tables to make this ask very simple:

As you can see above, I loaded the data into a table called dbtest.numberslist

Now to find out how many CallerNum are calling about multiple PhoneNum, a simple solution is to get a list of all distinct combinations of PhoneNum and CallerNum and then do a count of CallerNums from this distinct list. Since the list is distinct, a CallerNum calling in about the same PhoneNum will only appear once, so a CallerNum calling about multiple PhoneNums will appear multiple times.

So using temporary tables, I will create a table that holds the distinct call combinations

MySql (code is create temporary table <table name> then query to fill table

create temporary table distCalls
select distinct phonenum, callerNum from dbtest.numberslist;
Select * from distCalls -- shows what is in the table now

Now, lets see if we can find potential fraud callers, let us do a count of callerNum from the distinct temporary table

As you can see above, there are 4 numbers that have called about 4 distinct phone numbers during this time period. Again, this could be for legitimate reasons, but this is still something we look at when trying to find questionable activity.

MySQL Code

create temporary table distCalls select distinct phonenum, callerNum

from dbtest.numberslist;

SQL Server

Select distinct PhoneNum, CallerNum 
into #distCalls
from dbtest.numberslist

#tableName -- indicated temporary tables in SQL Server


Create volatile table distCalls as (
select distinct PhoneNum, CallerNum
from dbtest.numberslist)
with data
on commit preserve rows;

with data and on commit preserve rows are needed at the end if you want any data to be in your table when you go to use it


Create private temporary table distCalls as
select distinct PhoneNum, CallerNum
from dbtest.numberslist; 

Remember, temp tables delete themselves after each session (each time you log off the database). If you are working in the same session and need to recreate the temp table for some reason, you can always drop the table just as you would any other table object in SQL.

SQL Server: Linked Servers

SQL Server Linked Servers feature allows you to query data from other databases (even non SQL Server databases) from within SQL Server.

While I believe large data transfer jobs are best handled using an ETL solution like SSIS, sometimes all you want is a just a couple hundred rows of data from another database and setting up an ETL jobs might be overkill.

In this example, I am going to set up a link to a Teradata Data Warehouse.  This will allow me to query data from the warehouse and use it in my SQL Server environment.

(Note that you can connect to any database, such as another SQL Server or Oracle. I am just using Teradata as an example)

First go into SSMS and connect to your SQL Server

Now, in Object Explorer go to Server Objects -> Linked Servers


Right click on Linked Servers and select New Linked Server…


For a Teradata connection, I am choosing Microsoft OLE DB Provider for ODBC Drivers

(on a side note, you will need to have the ODBC driver for Teradata installed for this to work)


Linked Server = just whatever name you want to give your linked server – I chose EDW (short for Enterprise Data Warehouse)

Product Name = again free text, I just wrote Teradata to let people know what kind of product you are connecting too.

Data Souce: This is the server name you are trying to connect to


Next, click Security tab.

I want to use my own credentials to connect to Teradata so I clicked Be Made Using This Security Context: ( the green arrow)

Type in your Username and password. Click Ok


Now go to create a new query in SSMS (SQL Server Management Studio)

We will be using a function called OPENQUERY. The syntax is as follows




We can use the data returned from Teradata in SQL Server by simply putting it in a table or a temp table as shown below


We can also pass variables to our Teradata query. My preferred method is simply using a stored procedure.


       @USER VARCHAR(8) = NULL

declare @query varchar(8000) = 'Select * from OPENQUERY(EDW, ''SELECT USER_NM, LAST_NM, FIRST_NM FROM EMPLOYEE_TABLE WHERE USER_NM =  ''''' + @USER + ''''''')' 


exec [LINKED_SERVER_QUERY] @USER = 'blarson'