I have a column with many nulls in table 1, but now and then there is a value. If there is a value, I want to go to table 2 and take the the corresponding value from there. This should create an extra column called user_original:
CASE
WHEN table1.user_changed IS NOT NULL
THEN table2.user_original
ELSE -- do nothing
END as user_original
I basically want to replace
is nothing
Is this correct ? How can this be done? Is there a better way?
do you mean you need below
CASE
WHEN table1.user_changed IS NOT NULL
THEN table2.user_original
END as user_original
Do you want a correlated subquery?
(CASE WHEN table1.user_changed IS NOT NULL
THEN (SELECT table2.user_original FROM table2 WHERE table2.? = table1.?)
END) as user_original
The ? is for the columns that identifying "corresponding" values.
If this is the case, you can probably simplify this to:
(SELECT table2.user_original FROM table2 WHERE table2.? = table1.?) as user_original
My guess is there will be no matching value if the original value is NULL.
Related
Morning All! Essentially, I found out that a potential table.field I'd like to use may not have the information I want, so, I might have to look into a separate field. My below thought process is:
If table.field1 = NULL then pull the value from table.field2. If table.field2 = NULL then state "No Phone"
My current SQL statement in the select, cause it's in a certain format, is:
substring(view_episode_summary_current.patient_home_phone, 1, 3) || ' ' || substring(view_episode_summary_current.patient_home_phone, 5, 8)
Above is let's say table.field1. I'm assuming I'll need to create a CASE statement right? I just didn't know how long it could be?
(case when view_episode_summary_current.patient_home_phone = NULL then table.field2)
But I don't know how to get it to evaluate if table.field2 = null and display the value.
In many databases, you can use coalesce() to implement that kind of logic:
coalesce(t1.field1, t2.field2) as myfield
coalesce() returns the first non-null value across its arguments. So it gives you t1.field1 if it is not null, else it falls back on t2.field2. If both are null, you get a null value as a result.
You could also use a case expression - there is no benefit as compared to colaesce(), but this can handle more complex cases than just nullity checks
case
when t1.field1 is not null then t1.field1
when t2.field2 is not null then t2.field2
end as myfield
case stops on the first branch where the condition is fulfilled. If no branch matches, it returns null - you can put an else branch at the end of your code to return something else.
Note that both techniques requires both fields to have similar data types.
You do not show your actual query so I cannot show how to use that in your code.
I am trying to run this query where IN clause uses CASE to choose values between two cases.
The issue is with the hard coded value('aaa','bbb'). I cannot add multiple values inside THEN so it act as regular IN values. The hard code values will be dynamic as I will pass a variable for it.
select kdo.field0
from tb1 data1 inner join tb2 kdo
on kdo.field1 = 'xxx'
and kdo.field2::DATE >='2017-08-01'::DATE
and kdo.field0
in (case when 'asd'!='' then 'aaa','bbb'
else tb2.field0 end);
Also, I used a sub-query select inside THEN to get specific hard code values but it is also of no avail. Using single hard-coded value obviously works as usual.
Move your CASE outside IN:
select kdo.field0
from tb1 data1 inner join tb2 kdo
on kdo.field1 = 'xxx'
and kdo.field2::DATE >='2017-08-01'::DATE
and case when 'asd'!='' then kdo.field0 in ('aaa','bbb')
else kdo.field0=tb2.field0 end;
however I'm not sure what do you mean by 'asd'!='' since 'asd' is a string and this will always return true
also, else tb2.field0 end); part in your statement is not an array option, it's a column name so I assume this just translates to kdo.field0=tb2.field0 because if the previous case option is false you want to check if kdo.field0 is equal to any of values in tb2.field0 which is basically a join condition
This should be a simple one, but I have not found any solution:
The normal way is using an alias like this:
CASE WHEN ac_code='T' THEN 'time' ELSE 'purchase' END as alias
When using alias in conjunction with UNION ALL this causes problem because the alias is not treated the same way as the other columns.
Using an alias to assign the value is not working. It is still treated as alias, though it has the column name.
CASE WHEN ac_code='T' THEN 'time' ELSE 'purchase' END as ac_subject
I want to assign a value to a column based on a condition.
CASE WHEN ac_code='T' THEN ac_subject ='time' ELSE ac_subject='purchase' END
Now I get the error message
UNION types character varying and boolean cannot be matched
How can I assign a value to a column in a case statement without using an alias in the column (shared by other columns in UNION)?
Here is the whole (simplified) query:
SELECT hr_id,
CASE WHEN hr_subject='' THEN code_name ELSE hr_subject END
FROM hr
LEFT JOIN code ON code_id=hr_code
WHERE hr_job='123'
UNION ALL
SELECT po_id,
CASE WHEN po_subject='' THEN code_name ELSE po_subject END
FROM po
LEFT JOIN code ON code_id=po_code
WHERE po_job='123'
UNION ALL
SELECT ac_id,
CASE WHEN ac_code='T' THEN ac_subject='time' ELSE ac_subject='purchase' END
FROM ac
WHERE ac_job='123'
There is no alias in your presented query. You are confusing terms. This would be a column alias:
CASE WHEN hr_subject='' THEN code_name ELSE hr_subject END AS ac_subject
In a UNION query, the number of columns, column names and data types in the returned set are determined by the first row. All appended rows have to match the row type. Column names in appended rows (including aliases) are just noise and ignored. Maybe useful for documentation, nothing else.
The = operator does not assign anything in a SELECT query. It's the equality operator that returns a boolean value. TRUE if both operands are equal, etc. This returns a boolean value: ac_subject='time' Hence your error message:
UNION types character varying and boolean cannot be matched
The only way to "assign" a value to a particular output column in this query is to include it at the right position in the SELECT list.
The information in the question is incomplete, but I suspect you are also confusing the empty string ('') with the NULL value. A distinction that you need to understand before doing anything else with relational databases. Maybe start here. In this case you would rather use COALESCE to provide a default for NULL values:
SELECT hr_id, COALESCE(hr_subject, code_name) AS ac_subject
FROM hr
LEFT JOIN code ON code_id=hr_code
WHERE hr_job = '123'
UNION ALL
SELECT po_id, COALESCE(po_subject, code_name)
FROM po
LEFT JOIN code ON code_id=po_code
WHERE po_job = '123'
UNION ALL
SELECT ac_id, CASE WHEN ac_code = 'T' THEN 'time'::varchar ELSE 'purchase' END
FROM ac
WHERE ac_job = '123'
Just an educated guess, assuming type varchar. You should have added table qualification to column names to clarify their origin. Or table definitions to clarify everything.
The CASE expression is supposed to return a value, e.g. 'time'.
Your value is another expression subject ='time' which is a boolean (true or false).
Is this on purpose? Does the other query you glue with UNION have a boolean in that place, too? Probably not, and this is what the DBMS complains about.
I found the problem.
CASE WHEN hr_subject=’’ THEN code_name ELSE hr_subject END
The columns code_name and hr_subject was different length. This caused the unpredictable result. I think that aliases can work now.
Thank you for your support.
Here is my problem. I have a Microsoft SQL server database table with a bunch of columns in it. (I cannot change the data structure of this table!)
21 of the columns in this table stand for 'Actual' sizes
21 of the columns in this table stand for 'Relative' sizes
The Actual size columns correspond through Relative size columns via column number. (ex : ActualColumn1 corresponds to RelativeColumn1, ActualColumn2 corresponds to RelativeColumn2, ActualColumnX to RelativeColumnX up to 21)
Based on the inputted 'Actual' value I need to return the related 'Relative' value.
I have managed to do part of what I need with the following case statement, but case statements have a maximum of 10 conditions and therefore won't be able to cover all 21 columns in my table. What would be the best way to approach this issue? My goal would be to put this into a select statement so that I could select the Relative Size and return it in my query.
Example of what I did with the case statement:
SELECT
T.AValue
CASE WHEN (T.ActualColumn1 = T.AValue) then T.RelativeColumn1 ELSE
CASE WHEN (T.ActualColumn2 = T.AValue) THEN T.RelativeColumn2 ELSE
CASE WHEN (T.ActualColumn3 = T.AValue) THEN T.RelativeColumn3 ELSE
CASE WHEN (T.ActualColumn4 = T.AValue) THEN T.RelativeColumn4 ELSE
NULL
END
END
END
END AS RValue
FROM T
Thank you for your help!
If you change your case statement to a searched case you can have more then 10 when clauses.
select T.AValue,
case T.AValue
when T.ActualColumn1 then T.RelativeColumn1
when T.ActualColumn2 then T.RelativeColumn2
when T.ActualColumn3 then T.RelativeColumn3
when T.ActualColumn4 then T.RelativeColumn4
end as RValue
from T
I have below query in Ms-Access but I want to replace Blank value with zero but I can't get proper answer. Is there any way to replace blank value in zero.
(SELECT
SUM(IIF(Review.TotalPrincipalPayments,0,Review.TotalPrincipalPayments))+
SUM(IIF(Review.TotalInterestPayments,0,Review.TotalInterestPayments ))
FROM
tblReviewScalars as Review
INNER JOIN tblReportVectors AS Report ON(Review.LoanID=Report.LoanID)
WHERE Report.AP_Indicator="A" AND Report.CashFlowDate=#6/5/2011# AND Review.AsofDate=#6/5/2011# AND ( Review.CreditRating =ReviewMain.CreditRating)) AS [Cash Collected During the Period],
I assume TotalPrincipalPayments and TotalInterestPayments are both numeric types, hence the 'blanks' in question is the NULL value.
In SQL, the set function SUM will disregard NULL values, unless all values resolve to NULL in which case NULL is returned (erroneously and the error is with SQL not Access for a change :)
To use a simple example, SELECT SUM(a) FROM T; will only return NULL when a IS NULL is TRUE for all rows of T or when T is empty. Therefore, you can move the 'replace NULL with zero' logic outside of the SUM() function. Noting that "NULLs propagate" in calculations, you will need to handle NULL for each SUM().
You haven't posted the whole of your query e.g. the source of the correlation name ('table alias') ReviewMain is not showm. But it seems clear you are constructing a derived table named "Cash Collected During the Period", in which case your calculated column needs an AS clause ('column alias') such as TotalPayments e.g.
...
(
SELECT IIF(SUM(Review.TotalPrincipalPayments) IS NULL, 0, SUM(Review.TotalPrincipalPayments))
+ IIF(SUM(Review.TotalInterestPayments) IS NULL, 0, SUM(Review.TotalInterestPayments))
AS TotalPayments
FROM tblReviewScalars as Review
INNER JOIN tblReportVectors AS Report
ON Review.LoanID = Report.LoanID
WHERE Report.AP_Indicator = 'A'
AND Report.CashFlowDate = #2011-05-06#
AND Review.AsofDate = #2011-05-06#
AND Review.CreditRating = ReviewMain.CreditRating
) AS [Cash Collected During the Period], ...
An alternative to #onedaywhen's answer is to use the nz function, which is specifically for null-substitution:
SELECT
SUM(NZ(Review.TotalPrincipalPayments,0))+
SUM(NZ(Review.TotalInterestPayments,0))
...
As onedaywhen pointed out, this is functionally equivalent to putting the function outside the aggregate, which may perform better (the function is called once, rather than once per un-aggregated row):
SELECT
NZ(SUM(Review.TotalPrincipalPayments),0)+
NZ(SUM(Review.TotalInterestPayments),0)
...
To change a null value to a zero in an Access 2010 database, open your table, go to design view, click on the field and set the default value to: =0.