SQL - "incrementing" a char value causes collation error - sql

Question

I'm dealing with a table in which a bunch of arbitrary settings are stored as VARCHAR(255) values. The particular one I'm tasked with dealing with is a sequence number that needs to be incremented and returned to the caller. (Again, note that the sequence "number" is stored as VARCHAR, which is something I don't have any control over).
Because it's a sequence number, I don't really want to select and update in separate steps. When I've dealt with this sort of thing in the past with actual numeric fields, my method has been something like
UPDATE TABLE SET #SEQ_NUM = VALUE = VALUE + 1
which increments the value and gives me the updated value in one swell foop. I thought in this situation, I'd try the same basic thing with casts:
DECLARE #SEQ_NUM VARCHAR(255)
UPDATE SOME_TABLE
SET #SEQ_NUM = VALUE = CAST((CAST(VALUE AS INT) + 1) AS VARCHAR)
WHERE NAME = 'SOME_NAME'
The actual update works fine so long as I don't try to assign the result to the variable; as soon as I do, I receive the following error:
Msg 549, Level 16, State 1, Line 4 The collation
'SQL_Latin1_General_CP1_CI_AS' of receiving variable is not equal to
the collation 'Latin1_General_BIN' of column 'VALUE'.
I understand what that means, but I don't understand why it's happening, or by extension, how to remedy the issue.
As an aside to fixing the specific error, I'd welcome suggestions for alternative approaches to incrementing a char sequence "number".

Answer 1

From one of the comments, sounds like you may have already hit on this, but here's what I would recommend:
UPDATE TABLE
SET VALUE = CAST((CAST(VALUE AS INT) + 1) AS VARCHAR)
OUTPUT inserted.VALUE
WHERE NAME = 'SOME_NAME'
This will output the new value like a SELECT statement does. You can also cast inserted.VALUE to an int if you wanted to do that in the SQL.
If you wanted to put the value into #SEQ_NUM instead of outputing the value from the statement/stored procedure, you can't use a scalar variable, but you can pump it into a table variable, like so:
DECLARE #SEQ_NUM AS TABLE ( VALUE VARCHAR(255) );
UPDATE TABLE
SET VALUE = CAST((CAST(VALUE AS INT) + 1) AS VARCHAR)
OUTPUT inserted.VALUE INTO #SEQ_NUM ( VALUE )
WHERE NAME = 'SOME_NAME'
SELECT VALUE FROM #SEQ_NUM

Answer 2

Maintaining a sequential number manually is by no means a solution I'd like to work with, but I can understand there might be constraints around this.
If you break it down in to 2 steps, then you can work around the issue. Note I've replaced your WHERE clause for this example code to work:
CREATE TABLE #SOME_TABLE ( [VALUE] VARCHAR(255) )
INSERT INTO #SOME_TABLE
( VALUE )
VALUES ( '12345' )
DECLARE #SEQ_NUM VARCHAR(255)
UPDATE #SOME_TABLE
SET [VALUE] = CAST(( CAST([VALUE] AS INT) + 1 ) AS VARCHAR(255))
WHERE 1 = 1
SELECT *
FROM #SOME_TABLE
SELECT #SEQ_NUM = [VALUE]
FROM #SOME_TABLE
WHERE 1 = 1
SELECT #SEQ_NUM
DROP TABLE #SOME_TABLE

Answer 3

You can continue using the quirky update in OP but you have to split the triple assignment #Variable = Column = Expression in the UPDATE statement to two simple assignments of #Variable = Expression and Column = #Variable like this
CREATE TABLE #SOME_TABLE (
NAME VARCHAR(255)
, VALUE VARCHAR(255) COLLATE Latin1_General_BIN
)
INSERT #SOME_TABLE SELECT 'SOME_NAME', '42'
DECLARE #SEQ_NUM VARCHAR(255)
/*
-- this quirky update fails on COLLATION mismatch or data-type mismatch
UPDATE #SOME_TABLE
SET #SEQ_NUM = VALUE = CAST((CAST(VALUE AS INT) + 1) AS VARCHAR)
WHERE NAME = 'SOME_NAME'
*/
-- this quirky update works in all cases
UPDATE #SOME_TABLE
SET #SEQ_NUM = CAST((CAST(VALUE AS INT) + 1) AS VARCHAR)
, VALUE = #SEQ_NUM
WHERE NAME = 'SOME_NAME'
SELECT *, #SEQ_NUM FROM #SOME_TABLE
This simple rewrite prevents db-engine complaining on difference in data-type between #Variable and Column too (e.g. VARCHAR vs NVARCHAR) and seems like a more "portable" way of doing quirky updates (if there is such thing)