VB.NET（SQL）查询中的是否/其他语句？

Question

I just wanted to know what's the best way to add If/Else statements in a SQL query within VB.Net code?

This is my current query (doesn't work):

SELECT 
   FIRSTNAME, LASTNAME 
FROM 
   TBL_USERS 
ORDER BY 
   If(SortSelect() Is ""lastname"", LASTNAME, FIRSTNAME) 

Thanks in advance.

Answer 1

you could try something like this:

SELECT FIRSTNAME, LASTNAME 
FROM TBL_USERS 
ORDER BY Case when <SortSelect>= 'lastname' then LASTNAME else  FIRSTNAME end

Answer 2

My opinion about this is to NEVER put the IF in the SQL statement. It makes it too hard to read. Probably because it's all on the same line.

In your case, there's only one, but when you got many conditions, it gets almost impossible to read.

You should declare a string for your condition like this

Dim strQuery as string
Dim strOrderBy as string

If(SortSelect() = "lastname") then
   strOrderBy = "Order By lastname"
Else
   strOrderBy = "Order By firstname"
endif


strQuery = "SELECT FIRSTNAME, LASTNAME FROM TBL_USERS " & strOrderBy

Answer 3

Dim sql as string = "SELECT FIRSTNAME, LASTNAME FROM TBL_USERS ORDER BY "
if (SortSelect() = "lastname")
    sql = sql & "lastname"
else
    sql = sql & "firstname"
end if