I am trying to count price of all books. I need to make sure that if field is empty (it is NULL), then Book's value is 10. I have tried this:
SUM(CASE WHEN Value = NULL THEN 10 ELSE Value END) as main_value
But this doesn't do anything. It counts the sum fine, but when it finds empty field (null), it does not use value 10 in calculations.
What am I doing wrong?
If you just want to treat NULLs as 10s then COALESCE will do the trick:
The COALESCE function returns the first of its arguments that is not null. Null is returned only if all arguments are null.
So you could:
sum(coalesce(Value, 10))
To compare with null you need to use is null:
SUM(CASE WHEN Value is NULL THEN 10 ELSE Value END) as main_value
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.
Using Microsoft SQL Server, if you use COUNT(column name) it returns the number of rows in that column which have a non-null value (i.e., it counts the rows, ignoring nulls).
Is there any way to do something similar, but allowing you to tell it which values to ignore? For example, if I wanted to count all the rows in a table which have a value which is NOT 1, I could do something like COUNTNOT(column name,1). That would count all the rows in the specified column which have a value NOT 1.
You may use conditional aggregation:
SELECT COUNT(CASE WHEN some_val <> 1 THEN 1 END) AS cnt
FROM yourTable;
The above logic is that COUNT will count one whenever some value is not equal to 1. Otherwise, it falls on the ELSE conditional, which if not present defaults to the value NULL. Since NULL is not counted, any value other than 1 would contribute zero to the count.
Why not put what you want to exclude in a WHERE clause?
SELECT COUNT(some_val) AS cnt
FROM yourTable
WHERE some_val <> 1
You need to be careful about NULL values. I would recommend:
select sum(case when column in (<values to ignore>) then 0 else 1 end)
This will count NULL values as not in the list (even if NULL is in the list). To ignore NULL values (as well), switch the logic to:
select sum(case when column not in (<values to ignore>) then 1 else 0 end)
and be sure NULL is not in the list.
Based on one column within my query results (Value), I am trying to write an if/else statement based on the value held which will display the result the in an additional row.
For example, if I have a record of 2 within the value field, but I want to check whether it is above < 5. If the value is less than 5 I basically want the additional column to display a hardcoded value of 5, else display actual value.
Any help would be appreciated.
Use a case statement
select a.*,
case
when a.TheField < 5 then 5
else a.TheField
end as NewField
from MyTable a
You can use a case
select value, case when value < 5
then 5
else value
end as calculated_column
from your_table
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