使用CROSS JOIN

Question

I am learning how to use CROSS JOINS and I can't see what I am doing wrong with the one I am currently attempting.

What I have is a Pattern and Numbers table.

Number Table:
Numberid TinyINT

Pattern Table:
PatternID TinyINT IDentity(1,1)
Patternresult varchar(5)

I have already inserted each row in the Number table from 1 - 22.

At the moment I am getting no results displayed. But what I want to display is all the patterns between only numbers 0 - 5 (I can't include '0' in the number table as later on I will be using a table that requires a number beginning at '1' from the 'Number' table

e.g

0 - 0
0 - 1
0 - 2
0 - 3
0 - 4
0 - 5
1 - 0
1 - 1
1 - 2
1 - 3
1 - 4
1 - 5

etc

What am I doing incorrectly with my CROSS JOIN?

INSERT INTO dbo.Pattern(PatternResult)
SELECT cast(n.NumberID AS VARCHAR (5)) + ' - ' + cast(nn.NumberID AS VARCHAR (5)) AS PatternResult
FROM dbo.Number n
CROSS JOIN dbo.Number nn

Answer 1

Here you go.i have added ">0" in my query ,since i have numbers table starting from 0 ,you can ignore that..

    ;With Cte
    as
    (
    select 0 as n
    union all
    select top 5 Number from numbers where number>0
    order by number
    )
Insert into dbo.pattern
(
PatternResult
)
    select cast(c.n as varchar)+'-'+b.n
     from cte c
    cross join
    (select cast(n as varchar) from cte) b(n)
    order by c.n

Output:

0-0
0-1
0-2
0-3
0-4
0-5
1-0 and so on

Answer 2

your problems your number contains number from 1 to 22 and the PatternResult is only varchar(5)

so when you concatenate a 2 digits number, you will get PatternResult like '12 - 13' , which the length exceeded 5

And so your query should get truncation error and hence no result in the Pattern table.

Change the PatternResult to varchar(10) and it should work.

Answer 3

First, your query is an insert . Insert statements do not return result sets.

So, the question is, what does this return?

select *
from dbo.Pattern

Next, the pattern has space for five characters, but you are already using up three with ' - ' . So, try making it so the pattern can fit (by removing the spaces):

INSERT INTO dbo.Pattern(PatternResult)
    SELECT cast(n.NumberID AS VARCHAR (5)) + '-' + cast(nn.NumberID AS VARCHAR (5)) AS PatternResult
    FROM dbo.Number n CROSS JOIN
         dbo.Number nn;

Finally, when using VARCHAR() there really is no advantage to making the sizes too small. You might as well define the field as something like Patternresult varchar(255) so it will always be big enough for any result. When using CHAR() then a small value is important, because all the extra characters are stored as spaces.