Question

I am trying to create a work-flow with the help of SQL CE Database.

**Usr Table**
UID    FName    LName
 1      Tim      Lake
 2      June     Stone

**WFlow Table**
fID    Topic    InitBy    ApprovBy    PostedBy
1      Topic 1   2         NULL        NULL
2      Topic 2   1         NULL        NULL

UID and fID are Primary Keys and InitBy, ApprovBy, PostedBy are Foreign Keys linked to UID.

Now once the first topic is created fID=1, Topic=Topic 1, InitiBy=2, ApprovBy=NULL, PostedBy=NULL.

my SQL CE query looks like this.

Select WF.fID, WF.Topic, 
U1.FName + U1.LName as InitiBy,
U2.FName + U2.LName as InitiBy,
U3.FName + U3.LName as InitiBy,
from WFlow WF, Usr U1, Usr U2, Usr U3
where W.InitiBy = U1.UID
and W.ApprovBy = U2.UID
and W.PostedBy = U3.UID

This query returns no result. I am not able to handle the NULL in the ApprovBY and PostedBy columns.

appreciate your help.

Thanks,

i would also like to know how different the query will be in mySQL. in SQL-CE someone was able to help with the LEFT JOIN clause. but it does not seem to work in mySQL.

Answer 1

You need to use LEFT JOIN for this

Select  WF.fID, WF.Topic, 
        U1.FName + ' ' + U1.LName as InitiBy,
        U2.FName + ' ' + U2.LName as ApprovedBy,
        U3.FName + ' ' + U3.LName as PostedBy
from    WFlow WF 
        LEFT JOIN Usr U1
            ON WF.InitBy = U1.UID
        LEFT JOIN Usr U2
            ON WF.ApprovBy = U2.UID
        LEFT JOIN Usr U3
            ON WF.PostedBy = U3.UID

SQLFiddle Demo