Checking varchar data to see if it can be cast as decimal

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Checking varchar data to see if it can be cast as decimal

tarr94

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March 19, 2014 at 2:22 pm

#396448

Hi,
I have a varchar field. Most of the values in this field are numeric, and we need to update these to format them to display five decimal places.
If I simply try casting the values as decimals, then casting them back into varchar, I get an arithmetic overflow error. I assume this is because not all of the values in this field can be cast as decimals. Some of them contain nonnumeric characters.
Any ideas on how I can query the table to find the values that can't be converted to decimal would be greatly appreciated!
Thank you.

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Adam Angelini SSCrazy Eights Points: 8548 More actions · Answer 1

ISNUMERIC should get you most of the way there, but it will return 1 if it can be converted to any of these data types:

int

numeric

bigint

money

smallint

smallmoney

tinyint

float

decimal

real

Luis Cazares SSC Guru Points: 183706 More actions · Answer 2

You could try something like this:

WHERE somecolumn NOT LIKE '%[^0-9.]%'

This won't be completely safe as it will return false positives for values with more than one point(.).

Luis C.
General Disclaimer:
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tarr94 SSCommitted Points: 1684 More actions · Answer 3

Thanks for responding, Adam and Luis.

Unfortunately, after trying both of these methods, I still receive an error, "Error converting data type varchar to numeric". My update statement looks something like this:

UPDATE MyTable

SET MyField = CAST(CAST(MyField AS DECIMAL(10,5)) AS VARCHAR)

FROM MyTable

WHERE ISNUMERIC(MyField) = 1

AND MyField LIKE '%[^0-9.]%'

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 4

SQL Server will apply the filter and the conversion in whichever order results in the lowest cost - and in this case, the order chosen is breaking your query. Here's one way to ensure that they occur in the correct order:

DROP TABLE #MyTable

CREATE TABLE #MyTable (MyField VARCHAR(10))

INSERT INTO #MyTable VALUES ('100'),('101'),('102'),('103'),('10A'),('105'),('10B')

UPDATE t

SET MyField = x.MyField

FROM #MyTable t

CROSS APPLY (

SELECT MyField = CASE

WHEN MyField NOT LIKE '%[^0-9.]%' THEN CAST(CAST(t.MyField AS DECIMAL(10,5)) AS VARCHAR)

ELSE MyField END

) x

WHERE t.MyField NOT LIKE '%[^0-9.]%'

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

tarr94 SSCommitted Points: 1684 More actions · Answer 5

Chris,

I ran your query and it added the decimals where it should for the data you created.

But for whatever reason, I'm getting an arithmetic overflow error now when I try doing this with my data. I do notice some values include very large integers, or "$" signs, but there are many records, and I'm not sure how else to identify which ones aren't going to format correctly.

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 6

Can you augment the sample table in my last post to account for your observations? Thanks.

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

tarr94 SSCommitted Points: 1684 More actions · Answer 7

Thank you for your help everyone. I think I found the issue.

There some some numerical values that were greater than ten digits. I was trying to cast them into decimal (10,5). Once I filtered these out, the update ran fine.

ScottPletcher SSC Guru Points: 101123 More actions · Answer 8

Luis Cazares (3/19/2014)
You could try something like this:
WHERE somecolumn NOT LIKE '%[^0-9.]%'
This won't be completely safe as it will return false positives for values with more than one point(.).

WHERE

somecolumn NOT LIKE '%[^0-9.]%' AND

somecolumn NOT LIKE '%.%.%'

SQL DBA,SQL Server MVP(07, 08, 09) "It's a dog-eat-dog world, and I'm wearing Milk-Bone underwear." "Norm", on "Cheers". Also from "Cheers", from "Carla": "You need to know 3 things about Tortelli men: Tortelli men draw women like flies; Tortelli men treat women like flies; Tortelli men's brains are in their flies".