[Ur] checking for equality between optional and non-optional values in queries

[Adam Chlipala]

On 07/19/2015 07:20 AM, Todd Roth wrote:
> Another newbie question… How do you check for equality between optional and non-optional columns in different tables when doing join queries?  The following exampleQ query does not compile.  I get the errors shown in [1]
>
>
> table table2 : { Id : int, SomeVal : string}
> 	       PRIMARY KEY Id
>
> table table1 : { Id : int, Table2Val : option int }
> 	       PRIMARY KEY Id,
> 	       CONSTRAINT Table2Val FOREIGN KEY Table2Val REFERENCES table2(Id)
> 	
> fun exampleQ () = queryL (SELECT * FROM table1 LEFT JOIN table2 ON table1.Table2Val = table2.Id)

Here's the simple fix:

fun exampleQ () = queryL (SELECT * FROM table1 LEFT JOIN table2
                                      ON table1.Table2Val = 
{sql_nullable (SQL table2.Id)})