Selecting from two non-related tables at the same time

Suppose I have a table with lots of rows and columns (alias: bigtable), and a table that always has 1 row, but multiple columns (alias: 1rowtable). The 1rowtable has nothing to do with bigtable, it is just there for some settings my script uses that are modified dynamically. So I cannot use static SQLCMD variables for that and I cannot use normal variables for that either because my script has GO statements.

Now I want to write a select statement that accesses BOTH tables.

If I do:

SELECT ... FROM bigtable, 1rowtable

it does a CROSS JOIN so that is bad, can’t go that route.

If I use a CTE for 1rowtable, I have to access its fields with

SELECT field FROM 1rowtable

So that is bad too. Same with a table valued function like:

CREATE FUNCTION getSetting(@name nvarchar(40))
RETURNS TABLE
AS
RETURN (SELECT name FROM 1rowtable WHERE name = @name)

Obviously I cannot use a scalar function at all because it only returns a specific datatype, but the settings have different datatypes. Yet, obviously I would like to use it LIKE a scalar function of course without doing the ‘SELECT .. FROM dbo.getfieldfrom1rowtable(..)’ stuff, since I am using the 1rowtable rather often in queries.

I also tried doing:

SELECT
  (SELECT
     <expression involving bigtable and 1rowtable>,
     <expression involving bigtable and 1rowtable>,
     <expression involving bigtable and 1rowtable>,
     ...
  FROM 1rowtable)
FROM bigtable

But of course a subselect cannot select more than one item if it does not begin with exists…

So what should I do? It seems I will have to continue using ‘SELECT .. FROM dbo.getfieldfrom1rowtable(..)’ every time? Just curious 🙂

PS. ms sql server 2008r2

Answer

There is nothing wrong with using a cross join to bring together rows from tables, particularly when one only has one row.

Use the syntax:

select bt.*, ort.*
from bigtable bt cross join
     onerowtable ort

There is nothing inherently “wrong” with cross joins, when they are used correctly. The problem is when they are used inadvertently. If you cross join two tables with a million rows . . . well, your temp space is going to fill up, your processor(s) will be very busy, and the query will eventually crash due to a lack of resources.

However, cross joining a table with one row to another table poses no problems at all.

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Answer