CODEWITHSUNDEEP
sqlsql-servercastingnvarcharsql-convert
user2463808
user2463808

Reputation: 179

SQL error while converting varchar to int by joining two tables

I need to find missing numbers in my database. I am comparing two databases, tempdb created in query with numbers 1 - 999 and MYDAT.

MYDAT looks like:

+-------+
|  id   |
+-------+
| A-001 |
| A-002 |
| A-004 |
| A-... |
| A-952 |
| A-... |
+-------+

I am running this query:

declare @tempid int

set @tempid = 1

create table tempdb (tempid int)

while @tempid < 1000
begin
    insert into tempdb values(@tempid)
    set @tempid = @tempid + 1
end

select tempdb.tempid from tempdb
left join MYDAT on tempdb.tempid = CAST(SUBSTRING(MYDAT.ID, 3, 3) as INT)
where
MYDAT.ID IS NULL and
SUBSTRING(MYDAT.ID, 3, 3) <> '' and
SUBSTRING(MYDAT.ID, 3, 3) <> '000'and
SUBSTRING(MYDAT.ID, 3, 3)  NOT LIKE '%[^0-9]%'

drop table tempdb

Without droping temdb, select * from tempdb looks good and i am getting what i want.

The part with selecting and converting data from MYDAT works good and i am getting only integers

select CAST(SUBSTRING(MYDAT.ID, 3, 3) as INT) fom MYDAT
where 
SUBSTRING(MYDAT.ID, 3, 3) <> '' and
SUBSTRING(MYDAT.ID, 3, 3) <> '000'and
SUBSTRING(MYDAT.ID, 3, 3)  NOT LIKE '%[^0-9]%'

I am getting an error "converting varchar to int" but i have no idea why. When i change left join to right join, i get no errors.

I also checked both databases manually and there are no strings or characters, only integers.

I also tried the CONVERT() but with same result.

Any suggestions or ideas what is the problem?

Edit:

1 - I see one mistake as i tried it on rextester. I added MYDAT.ID IS NULL to the query so i get correct results.

2 - Examples I need this: http://rextester.com/KFG73206

But CAST or CONVERT just does not seems to work http://rextester.com/WJIAH52304

Upvotes: 0

Views: 442

Answers (3)

Gordon Linoff
Gordon Linoff

Reputation: 1269953

The problem is that the where clause is not necessarily executed before the on clause. SQL Server can rearrange the operations.

I would guess that you really want to compare to the first three characters of MYDAT.ID. That simplifies things a bit, because you can use LEFT() as in the code below. In fact, your where conditions don't look right, so I fixed them.

The best solution is try_convert():

select tempdb.tempid
from tempdb left join
     MYDAT
     on tempdb.tempid = try_convert(int, left(MYDAT.ID, 3) )
where MYDAT.ID <> '' and
      left(MYDAT.ID, 3) <> '000' and
      left(MYDAT.ID, 3) NOT LIKE '%[^0-9]%';

In pre-SQL Server 2012 versions, you can use a case instead:

select tempdb.tempid
from tempdb left join
     MYDAT
     on tempdb.tempid = (case when left(MYDAT.ID, 1, 3) not like '%[^0-9]%')
                              then convert(int, left(MYDAT.ID, 3)
                         end)
where MYDAT.ID <> '' and
      left(MYDAT.ID, 3) <> '000' and
      left(MYDAT.ID, 3) NOT LIKE '%[^0-9]%';

case does guarantee the order of evaluation.

Upvotes: 0

JGFMK
JGFMK

Reputation: 8904

You did say 'missing numbers' so things in tempdb that aren't in MYDAT are what you're after? If so see: http://rextester.com/HCB88714

Upvotes: 1

Rasanjana N
Rasanjana N

Reputation: 1400

Cannot clearly state the cause , may be an issue with data. You can try for some workaround to avoid casting,

 create table tempdb (tempid varchar(3))

while @tempid < 1000
begin
    insert into tempdb values(@tempid)
    set @tempid = @tempid + 1
end

select tempdb.tempid from tempdb
left join MYDAT on tempdb.tempid = SUBSTRING(MYDAT.ID, 3, 3)
where 
SUBSTRING(MYDAT.ID, 3, 3) <> '' and
SUBSTRING(MYDAT.ID, 3, 3) <> '000'and
SUBSTRING(MYDAT.ID, 3, 3)  NOT LIKE '%[^0-9]%'

Upvotes: 0

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