I have this error message:
Msg 8134, Level 16, State 1, Line 1 Divide by zero error encountered.
What is the best way to write SQL code so that I will never see this error message again?
I could do either of the following:
Add a where clause so that my divisor is never zero
Or
I could add a case statement, so that there is a special treatment for zero.
Is the best way to use a NULLIF clause?
Is there better way, or how can this be enforced?
In order to avoid a "Division by zero" error we have programmed it like this:
Select Case when divisor=0 then null
Else dividend / divisor
End ,,,
But here is a much nicer way of doing it:
Select dividend / NULLIF(divisor, 0) ...
Now the only problem is to remember the NullIf bit, if I use the "/" key.
In case you want to return zero, in case a zero devision would happen, you can use:
SELECT COALESCE(dividend / NULLIF(divisor,0), 0) FROM sometable
For every divisor that is zero, you will get a zero in the result set.
This seemed to be the best fix for my situation when trying to address dividing by zero, which does happen in my data.
Suppose you want to calculate the male–female ratios for various school clubs, but you discover that the following query fails and issues a divide-by-zero error when it tries to calculate ratio for the Lord of the Rings Club, which has no women:
SELECT club_id, males, females, males/females AS ratio
FROM school_clubs;
You can use the function NULLIF to avoid division by zero. NULLIF compares two expressions and returns null if they are equal or the first expression otherwise.
Rewrite the query as:
SELECT club_id, males, females, males/NULLIF(females, 0) AS ratio
FROM school_clubs;
Any number divided by NULL gives NULL, and no error is generated.
You can also do this at the beginning of the query:
SET ARITHABORT OFF
SET ANSI_WARNINGS OFF
So if you have something like 100/0 it will return NULL. I've only done this for simple queries, so I don't know how it will affect longer/complex ones.
You can at least stop the query from breaking with an error and return NULL if there is a division by zero:
SELECT a / NULLIF(b, 0) FROM t
However, I would NEVER convert this to Zero with coalesce like it is shown in that other answer which got many upvotes. This is completely wrong in a mathematical sense, and it is even dangerous as your application will likely return wrong and misleading results.
SELECT Dividend / ISNULL(NULLIF(Divisor,0), 1) AS Result from table
By catching the zero with a nullif(), then the resulting null with an isnull() you can circumvent your divide by zero error.
EDIT:
I'm getting a lot of downvotes on this recently...so I thought I'd just add a note that this answer was written before the question underwent it's most recent edit, where returning null was highlighted as an option...which seems very acceptable. Some of my answer was addressed to concerns like that of Edwardo, in the comments, who seemed to be advocating returning a 0. This is the case I was railing against.
ANSWER:
I think there's an underlying issue here, which is that division by 0 is not legal. It's an indication that something is fundementally wrong. If you're dividing by zero, you're trying to do something that doesn't make sense mathematically, so no numeric answer you can get will be valid. (Use of null in this case is reasonable, as it is not a value that will be used in later mathematical calculations).
So Edwardo asks in the comments "what if the user puts in a 0?", and he advocates that it should be okay to get a 0 in return. If the user puts zero in the amount, and you want 0 returned when they do that, then you should put in code at the business rules level to catch that value and return 0...not have some special case where division by 0 = 0.
That's a subtle difference, but it's important...because the next time someone calls your function and expects it to do the right thing, and it does something funky that isn't mathematically correct, but just handles the particular edge case it's got a good chance of biting someone later. You're not really dividing by 0...you're just returning an bad answer to a bad question.
Imagine I'm coding something, and I screw it up. I should be reading in a radiation measurement scaling value, but in a strange edge case I didn't anticipate, I read in 0. I then drop my value into your function...you return me a 0! Hurray, no radiation! Except it's really there and it's just that I was passing in a bad value...but I have no idea. I want division to throw the error because it's the flag that something is wrong.
Replacing "divide by zero" with zero is controversial - but it's also not the only option. In some cases replacing with 1 is (reasonably) appropriate. I often find myself using
ISNULL(Numerator/NULLIF(Divisor,0),1)
when I'm looking at shifts in scores/counts, and want to default to 1 if I don't have data. For example
NewScore = OldScore * ISNULL(NewSampleScore/NULLIF(OldSampleScore,0),1)
More often than not, I've actually calculated this ratio somewhere else (not least because it can throw some very large adjustment factors for low denominators. In this case I'd normally control for OldSampleScore is greater than a threshold; which then precludes zero. But sometimes the 'hack' is appropriate.
I wrote a function a while back to handle it for my stored procedures:
print 'Creating safeDivide Stored Proc ...'
go
if exists (select * from dbo.sysobjects where name = 'safeDivide') drop function safeDivide;
go
create function dbo.safeDivide( #Numerator decimal(38,19), #divisor decimal(39,19))
returns decimal(38,19)
begin
-- **************************************************************************
-- Procedure: safeDivide()
-- Author: Ron Savage, Central, ex: 1282
-- Date: 06/22/2004
--
-- Description:
-- This function divides the first argument by the second argument after
-- checking for NULL or 0 divisors to avoid "divide by zero" errors.
-- Change History:
--
-- Date Init. Description
-- 05/14/2009 RS Updated to handle really freaking big numbers, just in
-- case. :-)
-- 05/14/2009 RS Updated to handle negative divisors.
-- **************************************************************************
declare #p_product decimal(38,19);
select #p_product = null;
if ( #divisor is not null and #divisor <> 0 and #Numerator is not null )
select #p_product = #Numerator / #divisor;
return(#p_product)
end
go
Add a CHECK constraint that forces Divisor to be non-zero
Add a validator to the form so that the user cannot enter zero values into this field.
For update SQLs:
update Table1 set Col1 = Col2 / ISNULL(NULLIF(Col3,0),1)
There is no magic global setting 'turn division by 0 exceptions off'. The operation has to to throw, since the mathematical meaning of x/0 is different from the NULL meaning, so it cannot return NULL.
I assume you are taking care of the obvious and your queries have conditions that should eliminate the records with the 0 divisor and never evaluate the division. The usual 'gotcha' is than most developers expect SQL to behave like procedural languages and offer logical operator short-circuit, but it does NOT. I recommend you read this article: http://www.sqlmag.com/Articles/ArticleID/9148/pg/2/2.html
Here is a situation where you can divide by zero. The business rule is that to calculate inventory turns, you take cost of goods sold for a period, annualize it. After you have the annualized number, you divide by the average inventory for the period.
I'm looking at calculating the number of inventory turns that occur in a three month period. I have calculated that I have Cost of Goods sold during the three month period of $1,000. The annual rate of sales is $4,000 ($1,000/3)*12. The beginning inventory is 0. The ending inventory is 0. My average inventory is now 0. I have sales of $4000 per year, and no inventory. This yields an infinite number of turns. This means that all my inventory is being converted and purchased by customers.
This is a business rule of how to calculate inventory turns.
CREATE FUNCTION dbo.Divide(#Numerator Real, #Denominator Real)
RETURNS Real AS
/*
Purpose: Handle Division by Zero errors
Description: User Defined Scalar Function
Parameter(s): #Numerator and #Denominator
Test it:
SELECT 'Numerator = 0' Division, dbo.fn_CORP_Divide(0,16) Results
UNION ALL
SELECT 'Denominator = 0', dbo.fn_CORP_Divide(16,0)
UNION ALL
SELECT 'Numerator is NULL', dbo.fn_CORP_Divide(NULL,16)
UNION ALL
SELECT 'Denominator is NULL', dbo.fn_CORP_Divide(16,NULL)
UNION ALL
SELECT 'Numerator & Denominator is NULL', dbo.fn_CORP_Divide(NULL,NULL)
UNION ALL
SELECT 'Numerator & Denominator = 0', dbo.fn_CORP_Divide(0,0)
UNION ALL
SELECT '16 / 4', dbo.fn_CORP_Divide(16,4)
UNION ALL
SELECT '16 / 3', dbo.fn_CORP_Divide(16,3)
*/
BEGIN
RETURN
CASE WHEN #Denominator = 0 THEN
NULL
ELSE
#Numerator / #Denominator
END
END
GO
Filter out data in using a where clause so that you don't get 0 values.
Sometimes, 0 might not be appropriate, but sometimes 1 is also not appropriate. Sometimes a jump from 0 to 100,000,000 described as 1 or 100-percent change might also be misleading. 100,000,000 percent might be appropriate in that scenario. It depends on what kind of conclusions you intend to draw based on the percentages or ratios.
For example, a very small-selling item moving from 2-4 sold and a very large-selling item changing from 1,000,000 to 2,000,000 sold might mean very different things to an analyst or to management, but would both come through as 100% or 1 change.
It might be easier to isolate NULL values than to scour over a bunch of 0% or 100% rows mixed with legitimate data. Often, a 0 in the denominator can indicate an error or missing value, and you might not want to just fill in an arbitrary value just to make your dataset look tidy.
CASE
WHEN [Denominator] = 0
THEN NULL --or any value or sub case
ELSE [Numerator]/[Denominator]
END as DivisionProblem
This is how I fixed it:
IIF(ValueA != 0, Total / ValueA, 0)
It can be wrapped in an update:
SET Pct = IIF(ValueA != 0, Total / ValueA, 0)
Or in a select:
SELECT IIF(ValueA != 0, Total / ValueA, 0) AS Pct FROM Tablename;
Thoughts?
You can handle the error appropriately when it propagates back to the calling program (or ignore it if that's what you want). In C# any errors that occur in SQL will throw an exception that I can catch and then handle in my code, just like any other error.
I agree with Beska in that you do not want to hide the error. You may not be dealing with a nuclear reactor but hiding errors in general is bad programming practice. This is one of the reasons most modern programming languages implement structured exception handling to decouple the actual return value with an error / status code. This is especially true when you are doing math. The biggest problem is that you cannot distinguish between a correctly computed 0 being returned or a 0 as the result of an error. Instead any value returned is the computed value and if anything goes wrong an exception is thrown. This will of course differ depending on how you are accessing the database and what language you are using but you should always be able to get an error message that you can deal with.
try
{
Database.ComputePercentage();
}
catch (SqlException e)
{
// now you can handle the exception or at least log that the exception was thrown if you choose not to handle it
// Exception Details: System.Data.SqlClient.SqlException: Divide by zero error encountered.
}
Use NULLIF(exp,0) but in this way - NULLIF(ISNULL(exp,0),0)
NULLIF(exp,0) breaks if exp is null but NULLIF(ISNULL(exp,0),0) will not break
I am trying to connect a Filemaker DB to Firebird SQL DB in both ways import to FM and export back to Firebird DB.
So far it works using the MBS Plug-in but FM 13 Pro canot handle NULL.
That means that for example Timestamp fields that are empty (NULL) produce a "0" value.
Thats means in Time something like 01.01.1889 00:00:00.
So my idea was to simply ignore fields containing NULL.
But here my poor knowlege stops.
First I thought I can do this with WHERE, but this is ignoring whole records sets:
SELECT * FROM TABLE WHERE FIELD IS NOT NULL
Also I tried to filter it later on like this:
If (IsEmpty (MBS("SQL.GetFieldAsDateTime"; $command; "FIELD") ) = 0 ; MBS("SQL.GetFieldAsDateTime"; $command; "FIELD"))
With no result either.
This is a direct answer to halfbit's suggestion, which is correct but not for this SQL dialect. In a query to provide a replacement value when a field is NULL you need to use COALESCE(x,y). Where if X is null, Y will be used, and if Y is null then the field is NULL. Thats why it is common for me to use it like COALESCE(table.field,'') such that a constant is always outputted if table.field happens to be NULL.
select COALESCE(null,'Hello') as stackoverflow from rdb$database
You can use COALESCE() for more than two arguments, I just used two for conciseness.
I dont know the special SQL dialect, but
SELECT field1, field2, value(field, 0), ...FROM TABLE
should help you:
value gives the first argument, ie, your field if it is NOT NULL or the second argument if it is.
I have a query where it is subtracting from two columns and then dividing to generate a percentage complete. If the area hasn't been started it propduces NULL I would like it to instead show 00 or 0.
Here is my Query:
substr(count(process_locations.count_attempt_id)/count(processes.process_id),2,2) as "Percentage Complete"
I have try NVL, and COALESE, but am unsure where to place them I have tried a few combinations, but i Receive errors.
I have also tried a CASE WHEN ELSE END, but it still said null.
You may try like this:-
NVL(substr(count(process_locations.count_attempt_id)/count(processes.process_id),2,2),0) as "Percentage Complete"
Well, an unpopulated "area" is null unless the field is specified as "not null." If you have permissions, you might want to do that. Otherwise use NVL to substitute any NULLS with zeros.
I have this query in VB application on Access DB:
SELECT DISTINCT Specialization, MAX(a.faultZone) AS faultZone, ISNULL(a.faultCount, 0) AS NoOfFaults FROM Technicians AS t
LEFT JOIN
(
SELECT DISTINCT Faults.[Type] AS faultType, MAX(Faults.[Zone]) AS faultZone, COUNT(Faults.[Type]) AS faultCount
FROM Faults "
WHERE Faults.[Zone] = 8 " ' this value will be from variable
GROUP BY Faults.[Type] "
) AS a
ON (t.Specialization = a.faultType)
WHERE t.specialization <> 'None' "
GROUP BY a.faultCount, t.Specialization
It gives following problem that I can't solve...
"Wrong number of arguments used with function in query expression
'ISNULL(a.faultCount, 0'."
What I want to achieve is simply set value of NoOFFaults to zero, which would mean there are no faults in particular Zone.
Thank You
Just to add my two cents, and while I like the simple syntax of Nz(), if you seek trouble free performance, both IsNull() and NZ() should be avoided in favor of Is Null:
IIF(a.faultCount Is Null, 0, a.faultCount).
See the excellent explanation here: http://allenbrowne.com/QueryPerfIssue.html
Also, if your tables are in SQL Server or Oracle, using Nz() will force more of the query to be executed locally, with a HUGE performance impact.
Microsoft Access' version of IsNull is different than most SQL versions; it simply returns TRUE if the value is NULL, and FALSE if it isn't.
You need to basically build your own using IIF():
IIF(ISNULL(a.faultCount), 0, a.faultCount)
I think that you are looking for the nz function
Nz(a.faultCount, 0)
will return 0 if the value is null
I have the following SQL query:
select AuditStatusId
from dbo.ABC_AuditStatus
where coalesce(AuditFrequency, 0) <> 0
I'm struggling a bit to understand it. It looks pretty simple, and I know what the coalesce operator does (more or less), but dont' seem to get the MEANING.
Without knowing anymore information except the query above, what do you think it means?
select AuditStatusId
from dbo.ABC_AuditStatus
where AuditFrequency <> 0 and AuditFrequency is not null
Note that the use of Coalesce means that it will not be possible to use an index properly to satisfy this query.
COALESCE is the ANSI standard function to deal with NULL values, by returning the first non-NULL value based on the comma delimited list. This:
WHERE COALESCE(AuditFrequency, 0) != 0
..means that if the AuditFrequency column is NULL, convert the value to be zero instead. Otherwise, the AuditFrequency value is returned.
Since the comparison is to not return rows where the AuditFrequency column value is zero, rows where AuditFrequency is NULL will also be ignored by the query.
It looks like it's designed to detect a null AuditFrequency as zero and thus hide those rows.
From what I can see, it checks for fields that aren't 0 or null.
I think it is more accurately described by this:
select AuditStatusId
from dbo.ABC_AuditStatus
where (AuditFrequency IS NOT NULL AND AuditFrequency != 0) OR 0 != 0
I'll admit the last part will never do anything and maybe i'm just being pedantic but to me this more accurately describes your query.
The idea is that it is desireable to express a single search condition using a single expression but it's merely style, a question of taste:
One expression:
WHERE age = COALESCE(#parameter_value, age);
Two expressions:
WHERE (
age = #parameter_value
OR
#parameter_value IS NULL
);
Here's another example:
One expression:
WHERE age BETWEEN 18 AND 65;
Two expressions
WHERE (
age >= 18
AND
age <= 65
);
Personally, I have a strong personal perference for single expressions and find them easier to read... if I am familiar with the pattern used ;) Whether they perform differently is another matter...