Question

I’m selecting rows from a table

select name,age from tabl1

I need to add another column which should have the same value for the whole result set.
the value is comming from:

select value from config where key = 'company'

How can I combine this into one query ?

The resultset should look like

Name1 | Age1 | SameComapanyName
Name2 | Age2 | SameComapanyName
Name3 | Age3 | SameComapanyName
Name4 | Age4 | SameComapanyName

Answer 1

select t.name, t.age, c.value
from tabl1 t
cross join config c
where c.key = 'company'

Added:
It’s maybe more appropriate when there is need to return more than one column at time from specific table.

There is a difference in behaviour between this and subquery as a column. When condition c.key = 'company' isn’t met the join won’t return records at all, in case on subquery it returns null value for each row.

Added (after @alex comment):

cros join returns NxM records that is true but not in this case. Here where condition limits M to specific row/-s only. Sometimes NxM result might be even requirement then subquery won’t fulfil it.

Query (subquery version) fails when subquery returns more than one row or more than one column (that’s why other answers limits returned rows in subquery to one by top or max which is not always sufficient). cross join will do it without any problems, it’s is more elastic.

Tests done on tables:

create table species ( -- 9999 rows
    id int identity(1, 1), -- unique
    scientific varchar(50), -- not unique
    english varchar(50) -- unique
)

create table genus ( -- 2233 rows
    id int identity(1, 1), -- unique
    name varchar(50) -- unique
)

Before each query I’ve run:

dbcc freeproccache
dbcc dropcleanbuffers

Query:

select s.*, g.name
from species s
cross join genus g
where g.name = 'Pinaroloxias'

Execution plan:

Stats:

SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 5 ms.

(9999 row(s) affected)
Table 'species'. Scan count 1, logical reads 79, physical reads 0, read-ahead reads 79, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'genus'. Scan count 1, logical reads 12, physical reads 11, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(4 row(s) affected)

SQL Server Execution Times:
   CPU time = 46 ms,  elapsed time = 224 ms.

Query:

select s.*, (select g.name from genus g where g.name = 'Pinaroloxias')
from species s

Execution plan:

Stats:

SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 5 ms.

(9999 row(s) affected)
Table 'Worktable'. Scan count 1, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'genus'. Scan count 1, logical reads 12, physical reads 11, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'species'. Scan count 1, logical reads 79, physical reads 0, read-ahead reads 79, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(8 row(s) affected)

SQL Server Execution Times:
   CPU time = 31 ms,  elapsed time = 224 ms.

Query:

select s.*, (select max(g.name) from genus g where g.name = 'Pinaroloxias')
from species s

Execution plan:

Stats:

SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 31 ms.

(9999 row(s) affected)
Table 'species'. Scan count 1, logical reads 79, physical reads 0, read-ahead reads 79, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'genus'. Scan count 1, logical reads 12, physical reads 11, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(6 row(s) affected)

SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 229 ms.

The test would be better if I had done it many times and calculated the average but I had no time for that.