query multiple tables with columns based on multiple conditions - tsql

Question

I have three columns: crew info, training info, position info. I am trying to create a report that shows the most recent date of certain trainings that each crew member has taken. Each training should have its own column but some trainings are only required for certain positions.
I have tried a case statement statement as well as just filtering in a where statement but keep getting errors. Some of the research did says that t SQL doesn't have an if statement but some says it does.
Here is the Access code that works: Ballast Water Management:
Max(IIf([CURRENT_FLAG]=1 And [QUALIFICATION_ID] In (14800000086) And [CMC_POS_CODE_TRANSLATOR] In (1,3,6,8,12,13,15,18,20,25,32,90,91,92,94,96,98,100,102,103,230),[ISSUED_ON],IIf([CMC_POS_CODE_TRANSLATOR] Not In (1,3,6,8,12,13,15,18,20,25,32,90,91,92,94,96,98,100,102,103,230),"","0")))
What I want is to either show the latest date that a crew member completed the training (if required), a blank if it's not required for them, or a 0 if it's required and they don't have it.

Answer 1

Okay, one of the problems you have is that you are essentially returning three data types:
a date (possibly even a datetime);
a BIT (0/1);
an empty string (VARCHAR).
So you need some way to handle all three. I assumed that you would want:
a date in YYYYMMDD format as a string;
the 0 is a string of "0";
the empty string is already a string.
So your query becomes this:
SELECT
MAX(
CASE
WHEN [CURRENT_FLAG] = 1
AND [QUALIFICATION_ID] = 14800000086
AND [CMC_POS_CODE_TRANSLATOR] IN (1,3,6,8,12,13,15,18,20,25,32,90,91,92,94,96,98,100,102,103,230)
THEN CONVERT(VARCHAR(8), [ISSUED_ON], 112)
ELSE
CASE
WHEN [CMC_POS_CODE_TRANSLATOR] NOT IN (1,3,6,8,12,13,15,18,20,25,32,90,91,92,94,96,98,100,102,103,230)
THEN ''
ELSE '0'
END
END)
FROM
MY_TABLE;
If this doesn't work what might help is showing us what you tried, and the actual error you got?
Also, TSQL does indeed allow use of IF statements, but not inside a SELECT query. So you could do this:
IF #my_dog_has_no_nose = 1
BEGIN
SELECT 'how does he smell?' AS question;
ELSE
SELECT NULL AS question;
END;
But in a SELECT statement you will have to use CASE to allow redirection.