Re: [libreoffice-users] Re: Base scenario

 Comment inline below.

--Dan

On 01/08/2013 07:07 PM, Girvin R. Herr wrote:
> Ian,
> Have you actually drawn any relationships?  Base will not do that for 
> you.  Just adding the tables in the 'Relationships Window' will not 
> create the relationships automagically.  You must click and hold on 
> the one table element (remote key) and drag over to the related 
> table's element (primary key), then release the mouse button.  Base 
> will then draw a line between the two.  Note, the order of the drag is 
> important.  It determines the type of join. Joins are confusing to me 
> too, so I can't help much there.  I had to experiment with the 
> direction to get it to work right.  I think it was remote key to 
> primary key, but I am not sure of that any more.
>
> Warning!  The way the SQL language is set up, if either of the ends of 
> a join (relationship) is NULL, then the record will be discarded and 
> not show up in your result set.  No warnings, no errors.  Data records 
> will just be missing.  IMHO, this is stupid (my mantra is: "thou shall 
> not lose data"), but that is how the SQL language was set up.  So, 
> make sure any joined data elements in all of your table records are 
> not NULL.  Note that NULL is not zero (0) and vice-versa!  NULL means 
> that there is no data in the record element.  I use a lot of remote 
> keys in my database main tables that point to primary keys (options) 
> in other tables.  In those other tables, I have made it a point to 
> make the data elements of the first record to be "-", which is my 
> equivalent of unknown, just to have something to select that is not 
> NULL.  You could probably use a blank (" "), but I prefer seeing the 
> "-" in forms and reports.  Most times in reports, it is hard to see 
> anyway.  Seeing the "-" tells me the field is not NULL.
> Hope this helps.
> Girvin Herr
      These statements about joins do not seem to be quite correct. 
What you are describing is an Inner Join: you will only see the rows of 
data in which both the foreign (remote) key and the primary key have a 
value.
     Suppose we have two tables A and B and that the foreign (remote) 
key is in table A and the primary key is in table B.
    Example 1: table A Left Outer Join table B. The output (result set) 
for this contains all the fields in table A and their values on the left 
side of the combined table. The right side contains all the fields in 
Table B. The rows in which the primary key value matches the foreign key 
value, data from both table appear in the output. However, where there 
is no primary key value in table B that matches the foreign key value in 
table A, all the fields from table B for that row will be NULL.
     Example 2: table A Right Outer Join table B. The output for this 
contains all the fields in table B and their values on the right side. 
For each output row in which the foreign key does not have a value that 
matches any value of the primary key, the fields in the left side of it 
will be NULL.
     Example 3: table A Cross Join table B. This is also referred to as 
a Cartesian Product. In this case, each row of table A is joined to all 
the rows of table B. This contains all of the possible combinations of 
combining both tables. Usually, some rows of the output will have the 
table A fields all showing NULL while others will have the fields of 
table B showing all NULL.

> Ian Whitfield wrote:
> > Hi All
> >
> > Re - My previous post.... Have been doing some Googling etc and found 
> > the 'Relationships Window' for setting Relationships.
> >
> > I can get the Window up, select my Tables but it _DOES NOT_ draw any 
> > connecting lines or set any Relationships!!??
> >
> > Is this another "Gotcha" of using MySQL and Base together? As it does 
> > _NOT_ seem to work at all!!
> >
> > I'm using PCLinuxOS 2012, LO Base 3.6.2.2 and MySQL 5.1.55
> >
> > IanW
> > Pretoria RSA.


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