SQL Server query stuck when adding order by clause - sql

Question

I'm working on writing some queries for a very large (and messy) database on behalf of a client. So far, I've just been grabbing the columns I need and making sure that they contain the data I'm looking for. There have been no issues up until I add anything to my "order by" clause. When I add an order by clause to my query, the SQL Server remains stuck on "executing query." Example of code below:
SELECT TOP 100
PEATR.[EffectiveDate] AS 'Effective Date',
CustomerRoot.[CustomerName] AS 'Name',
CustomerAddressRoot.[Street1] AS 'Address 1',
CustomerAddressRoot.[Street2] AS 'Address 2',
CustomerAddressRoot.[City],
CustomerAddressRoot.[State],
CustomerAddressRoot.[Zip],
CustomerAddressRoot.[Country],
CustomerAddressRoot.[AddressDesc] AS 'Description'
FROM PrEmployeeAccrueTierRoot AS PEATR, CustomerRoot, CustomerAddressRoot
ORDER BY CustomerRoot.[CustomerName]
I have also tried creating an inner join on CustomerRoot and CustomerAddressRoot, as the query is returning repeat data, especially in the "Address 1" column. When I ran the code below, I have received the following error message:
The objects "CustomerRoot" and "CustomerRoot" in the FROM clause have the same exposed names. Use correlation names to distinguish them.
Code:
SELECT TOP 100
PEATR.[EffectiveDate] AS 'Effective Date',
CustomerRoot.[CustomerName] AS 'Name',
CustomerAddressRoot.[Street1] AS 'Address 1',
CustomerAddressRoot.[Street2] AS 'Address 2',
CustomerAddressRoot.[City],
CustomerAddressRoot.[State],
CustomerAddressRoot.[Zip],
CustomerAddressRoot.[Country],
CustomerAddressRoot.[AddressDesc] AS 'Description'
FROM PrEmployeeAccrueTierRoot AS PEATR, CustomerRoot, CustomerAddressRoot
INNER JOIN CustomerRoot ON CustomerAddressRoot.CustomerId=CustomerRoot.CustomerId
I did assign aliases to all of the tables previously, though I was still returning the same error message. Any guidance or suggestions would be much appreciated.

Answer 1

You are performing a cartesian join.
FROM PrEmployeeAccrueTierRoot AS PEATR, CustomerRoot, CustomerAddressRoot
...is the same as...
FROM PrEmployeeAccrueTierRoot AS PEATR
inner join CustomerRoot on 1=1
inner join CustomerAddressRoot on 1=1
There is no join logic.
So, if PrEmployeeAccrueTierRoot has 1000 rows and CustomerRoot has 1000 rows and CustomerAddressRoot has 1000 rows, your result will have 1,000,000,000 rows.
Try two things:
Include join logic.
Your query should look something like this:
SELECT TOP 100
PEATR.[EffectiveDate] AS 'Effective Date',
CustomerRoot.[CustomerName] AS 'Name',
CustomerAddressRoot.[Street1] AS 'Address 1',
CustomerAddressRoot.[Street2] AS 'Address 2',
CustomerAddressRoot.[City],
CustomerAddressRoot.[State],
CustomerAddressRoot.[Zip],
CustomerAddressRoot.[Country],
CustomerAddressRoot.[AddressDesc] AS 'Description'
FROM PrEmployeeAccrueTierRoot AS PEATR
inner join CustomerRoot on CustomerRoot.customerrootid = peatr.customerrootid
inner join CustomerAddressRoot on CustomerAddressRoot.customerrootid = CustomerRoot.customerrootid
ORDER BY CustomerRoot.[CustomerName]
Of course, I don't know what columns you should actually join on. Know thy data.
Then you'll have one problem remaining: If your query (without the TOP 100) would return millions of rows, you're asking the database server to perform all of the logic and gather all of the rows, then sort them by CustomerName, then return the first 100 rows. That could still be slow. You'll want to...
Apply filters.
SELECT TOP 100
PEATR.[EffectiveDate] AS 'Effective Date',
CustomerRoot.[CustomerName] AS 'Name',
CustomerAddressRoot.[Street1] AS 'Address 1',
CustomerAddressRoot.[Street2] AS 'Address 2',
CustomerAddressRoot.[City],
CustomerAddressRoot.[State],
CustomerAddressRoot.[Zip],
CustomerAddressRoot.[Country],
CustomerAddressRoot.[AddressDesc] AS 'Description'
FROM PrEmployeeAccrueTierRoot AS PEATR
inner join CustomerRoot on CustomerRoot.customerrootid = peatr.customerrootid
inner join CustomerAddressRoot on CustomerAddressRoot.customerrootid = CustomerRoot.customerrootid
WHERE CustomerAddressRoot.State = 'Alaska'
ORDER BY CustomerRoot.[CustomerName]
..at least during testing, to speed things up.