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Dan Lewis wrote:
 Comment inline below.


On 01/08/2013 07:07 PM, Girvin R. Herr wrote:
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.

Your and Winston's explanations of joins cleared up a lot of my misunderstanding of them. You can only get so much from books. The fact that my using an Inner Join requires non-null values to get a complete result set makes a lot of sense now. If I now understand correctly, I should be using a Left Outer Join. That way I always get the "table A" data in the result set, but "table B" data may be null if there is no match to "table A". That is the response I was looking for. I just tried it and it does give me the same result set information (no records missing) as the Inner Join. However, I have no Null values in "table A". It may take me a little while to test it with Nulls in the Left ("table A") side. I also recant and apologize for my "stupid" remark about SQL losing data. The reasons for the missing data are now apparent to me and that remark was premature. While I was doing this join editing testing on my sample query, I took time to look at the order of joining in the Query Design window and it looks like in order to get the main table (with foreign key) as "table A", I had to first click on the "sub" table ("table B") element and then drag to the "table A" element. In other words, it needs to be primary key -> foreign key. My original response to Ian was not sure of this drag order. In any case, the Join Properties dialog and prompt show the correct order in the "Fields Involved" window, with "table A" in the left column and "table B" in the right column.

Thanks for the help.
Girvin Herr

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