I was trying to get the nulls on doing a SUM() function on sql and I figured out that sql now consider nulls, so if a column has a different value and a null value the sum is good calculated. For example I have the column SUM_EXAMPLE with the different values: NULL - 3 - 4 - NULL - 6
So if I execute the next query: select sum(SUM_EXAMPLE) FROM TABLE T the result is 13 and not null.
And if I have another column SUM_COLUMNS only with NULL the result of select sum(SUM_COLUMNS) FROM TABLE T is NULL. It has been a change or a improvement of oracle so it does this function right without using functions like isNull or NVL?
Thank you
Aggregate functions (SUM, AVERAGE etc) generally ignore NULL values. Therefore if there is at least one non null value in the column, you will get a non null result.
If all values in a column being aggregated are null, there is pretty much no other option but to return null as the result.
Note that this is different to how scalar functions behave. For example: "Select x + y" will return null if either x, y or both are null. You will only get a non null result for this if both x and y have non-null values.
Related
I have the following table in Postgresql. The first 4 records are the base data and the others were generated with the ROLLUP function.
I want to add a column "grp_1" that will display the first non-null value of the columns grp1_l1, grp2_l2 and grp2_l3
I can get to the desired result by nesting 3 "case" functions using the SQL below, but my real table has 4 groups with each 8 to 10 columns (so a lot of nested "case" function).
sql:
SELECT grp1_l1, grp1_l2, grp1_l3, case when grp1_l1 is not null then grp1_l1 else case when grp1_l2 is not null then grp1_l2 else case when grp1_l3 is not null then grp1_l3 else null end end end as grp1, value
FROM public.query_test;
Is there a better and more scalable to handle this requirement ? Any suggestions are welcome.
The id will not always have 3 digits, that is just the case in my example here
Use coalesce() it's defined as "returns the first of its arguments that is not null" - which is exactly what you want.
coalesce(grp1_l1, grp1_l2, grp1_l3)
I'm using the below command to find the sum of records from 8 columns but getting null in the O/P as shown below.
Command part 1
command part 2
Output
How can this be fixed?
Yes, the thing is NULL + something results NULL. To solve this, wrap each sum() in the NVL(sum(),0), so if some particular sum() is NULL, it is converted to 0 and the whole total will be not null:
nvl(sum(case when col1='something' then 1 else 0 end),0)+ ...
Or always use else 0, like in the first expression (H).
Wrapping with NVL() will solve the problem even if column comes from the join and the rows are absent and sum is NULL.
just a simple question but somehow I can't find an answer here.
I have two columns (A and B). Both contains numbers with zeros and null. I would like to get a division one by the other to get information about the ratio between each single row but I am getting ORA-01476.
I know the divisior is equal to zero but I would like to get in this row a number and not an error for whole query
A B
1 5
2 Null
3 0
NULL 3
0 4
4
I am using sql developer.
If you divide a number by zero you get an error, because the answer to such division is undefined. SQL, however, has a value for undefined: NULL. So make the result NULLinstead:
select a, b, case when b = 0 then null else a / b end as ratio
from mytable;
or
select a, b, a / case when b = 0 then null else b end as ratio
from mytable;
This is standard SQL and works in Oracle as well as in about every other RDBMS. Oracle also provides the function NULLIF as a shorter way to write the expression in the second query.
You can use nullif to return null instead of raising an error:
select A / nullif(B, 0) as division
from YourTable
If your numbers are stored as varchar, cast them to numbers before using them:
select to_number(A) / nullif(to_number(B), 0) as division
from YourTable
Given table:
ID ONE TWO
X1 15 15
X2 10 -
X3 - 20
This query:
SELECT (ONE + TWO) FROM (TABLE)
Just returns the sum of X1's values but not the others since at least one column has a null value. How can I still add them even if there is a null? i.e. consider the null as a 0 maybe?
SELECT (COALESCE(ONE, 0) + COALESCE(TWO, 0)) FROM (TABLE)
COALESCE will return the first non-null value found in the parameters from left to right. So, when the first field is null, it will take the 0.
That way, X2 will result in 10 + 0 = 10
there is already a good answer, but I think it is worth mention to the antonpug (in case he doesn't know) that the reason why this is happening is that NULL is not a value that can be compared or summed.
NULL isn't 0 or '' (empty string), so every operation involving NULL will result NULL (10 + NULL = NULL), even (NULL=NULL) will evaluate to FALSE
I am using SQL Server 2005 BOXIR2.
My doubt, from universe table there is an eventcode having different types of codes like Enquiry,FollowUp,LostofSales,Contact,etc
I make a measure that is from object properties formula count(Tablename.EventCode)save and export it, when I used this EventCode in Webireport, it show values for paricular EventCode, but zero values are not read it show null blank as below example .
I WANT TO GET THE ZERO VALUES FOR WHICH IT IS IN BLANK(NULL).
count(Tablename.EventCode)
Enquiry,FollowUp,LostofSales,Contact
10 20 15
5 12 5
6 4 3
Can u please help me how to get get zero values for null,Formula
I'm not sure exactly what you are asking, but I think you may be looking for ISNULL()
SELECT ISNULL(table_name.column_name, 0)
will return 0 if table_name.column_name is null
If you're getting NULLs when performing an aggregate, it's probably because one of elements is NULL. All you need to do is coalesce those entries to a known value (such as zero).
SELECT COUNT(COALESCE(Tablename.EventCode, 0)) FROM Tablename