I am building an Access database, but am having an issue with the relationships. I have 2 unique and indexed field columns in one table, and one indexed (but not unique) one.
I want to either :
A) Set the second table to allow me to simply fill in one field with the primary key of the first table, and have it fill in the rest of the information automatically based on that.
or
B) Be able to select the non-unique entry (they are prices- hence my inability to simply make them unique) from a drop down on the second table.
Related
I'm using Access 2007. I have two tables, first one has a PK (primary key), but the second has not.
When using a query linking the two tables on the PK, I need the rows have the same sort as it is in the second table (means as records has been entered), but this doesn't happen by default, I don't know why!
Tables are just a big bucket that holds data. There is no order to them unless you supply it. Therefore, in order for the items in your query/table to appear in the order that they were entered you will have to supply something that allows Access to apply this sorting for you.
You should add an AutoNumber Primary Key to the DataSub table. This will automatically increase every time that you add new data to this table, and so you can then use this in any queries to sort by.
Regards,
We'd like to prevent record duplication in our MS access database using a multicolumn unique index. Because of how the data is sent (via network), duplicate data is sometimes received. The data source does not send a unique ID, so the simplest option is to prevent duplicate records being inserted.
According to Unique Index Design Guidelines:
With multicolumn unique indexes, the
index guarantees that each combination
of values in the index key is unique.
For example, if a unique index is
created on a combination of LastName,
FirstName, and MiddleName columns, no
two rows in the table could have the
same combination of values for these
columns.
This is for SQL 2005 however, so I'm not sure it's possible using MS access.
I guess an alternative is to perhaps use the query (pseudo code):
insert into foobar (a, b, c) values ('x', 'y', 'z')
where (a <> 'x') and (b <> 'y') and (c <> 'z')
... but I feel like an index would be better.
Turns out you can create a multi-column unique index on an MS access database, but it's a little crazy if you want to do this via the GUI. There's also a limitation; you can only use 10 columns per index.
Anyway, here's how you create a multi-column unique index on an MS access database.
Open the table in design mode, and Design, select Indexes.
Create a new row and enter a value in the Index Name cell,
Choose the first column from the drop down menu.
Add a new row and leave the Index Name cell blank.
Choose the second column, and so on.
Here's what it should look like:
Open the table in design view in MS Access, select the three columns that you want to make into the unique index, and then click the little key on the toolbar. You cannot have null values in a primary key (set).
We can make multi data to be unique data without set them as primary key.
(Note: only 1 data in the table can be primary key)
Step to set the data value as unique data (for MS ACCESS 2007 - 2010)
Open selected table in Design View
Click (Highlight) the specific column/attribute that you wish to set as unique
At the bottom of the table you will see "Index Properties" for that specific column
Find "Indexed" column, currently the data in Indexed text box is "No", change the data by click at the end of text box, choose "Yes(No Duplicates)"
Really hopes this methods can helps all of you! :)
I had the problem Nick Bolton reported above. Setting 2 fields (Foo, Bar) as PK set Foo to unique, when I wanted only the combination of Foo + Bar to be unique.
The problem turned out to be that I had created a 1:1 relationship to another table, linking on Foo. I deleted the relationship, set up the 2-field PK the way I wanted, and then reinstated the relationship, and it works as desired.
A trick I found is that in order to get a 2 column primary key (in the parent table) to be a child table´s 2(FK)+n primary key is to FIRST CHOOSE the indexed attribute as FISRT key attribute and THEN the not indexed attribute as a SECOND key attribute in the "Modify Relations Dialog Box" #Relations Window.
It will serve as Unique key in Ms Access 2007/2010
I've seen various posts here about not using lookup within a table. If you don't, how do you enforce referential integrity between a field and the allowable values from a lookup table? I can't create a relationship between the table field and the field in the lookup table because I can't create a unique (no duplicates) index on the field - the particular value needs to appear multiple times across the records in the table. But if I use the field properties to set a lookup on it and specify the field from the lookup table that it must contain, then this ensures that data can't be entered into this field that isn't in the lookup table.
Or have I got completely the wrong end of the stick here?
I recommend that you always create forms for editing records. And in those forms you can create combo boxes that perform the lookups in the correct table and field. There are options there so that you can limit the data entry to only those values which are stored in the table. This option is called Limit To List (you'll see it in the combo properties).
Another important way to enforce that data exists in your lookup table is through your Relationships.
tblProducts
ProductID (primary key)
CategoryID (foreign key)
ProductDescription
tblCategories
CategoryID (primary key)
Category
In the relationships window you would define a relationship between the two tables above on the CategoryID field. You are accomplishing several things here. It's more efficient to store only the CategoryID in your Products Table since you will be storing less data. Also, this way if you change the name on the category all records will reflect that change immediately. Every place that you display a product with its category you will need to create a combo box so that you display the Category Description as opposed to displaying the CategoryID.
As a side note, I recommend that you rarely use the Value List option as the Row Source Type in a combo. Using the Table/Query option and then creating an appropriate lookup table is a much more robust and flexible design.
So the root of this problem may lie in poor database design, some of the way this is set up is inherited from older versions. I just couldn't figure out a better way to do this.
I have four tables linked by the same field: [OBJECTID]. Each table is linked to an Access Form that controls the data. It is important that these tables be separate as the data is georeferenced and needs to be mapped separately, however they inherit several fields from one another by default.
Most of the time, the tables are in a one-to-one-to-one-to-one relationship, however occasionally, there is only data for the first table, and occasionally, there is only data for the second, third and fourth form.
Right now, the [OBJECTID] field in the first table is set to datatype autonumber, so that all subsequent linked records in the other tables can inherit that number. For the cases where the record in Tbl1 are not entered via Form1, it is easy enough to just assign a number that does not conflict with any current number, but how do I avoid assigning a number that could conflict with some future [OBJECTID] generated by the autonumber field in Tbl1?
Sorry if that is confusing! Thanks in advance for helping me think this through....
If the design is correct, there should be a relationship with referential integrity between tbl1 and table 2/3/4. Since you mention that occasionally, there is only data for the second, third and fourth form that means we have no referential integrity here :-/.
I would identify the fields that are common to all 4 tables, and create a "main" table with those, meaning that the main table MUST be filled. Then you create a 1 to 0,1 relationship to the other 4 tables, with an outer join, their PK beeing then a Long Integer.
For the source of your forms 1 to 4, use an outer join between MainTable and T1/2/3/4. The "subtables" will then inherit the PK of the main table.
Hope I am not too obscure.
I've got the following situation: I want to store data, which represents, if a user is following another user. Another table, which I cannot touch, stores the users, where the username is the primary key (unfortunatly no id...).
The fact is, if one user follows another one, it doesn't mean, that the other one is following the first one.
Right now, I designed the table with two varchar's (128) and a UNIQUE INDEX on these two varchar's which represent the usernames.
The problem is, that I need to parse some old-styled system now, and I finished like 15% and I've got 550k entries on this table already.
The index is bigger then 16MB, and the data just 14MB.
What could I do, to save this data in a better way? As said, I cannot use id's instead of the usernames, because the user-table uses the username as primary key.
As you have noticed, creating a seperate index on all columns essentially forces MySQL to duplicate all data in the index.
Instead of creating a seperate unique index, you can create a primary key consisting of both of your fields. MySQL uses the primary key as a clustered index making sure your uniqueness constraint is still satisfied without increasing the size of your database.
You might consider building your own index table that contains ID > username.
You could then use the ID's to map the followers.
This will cause for some extra overhead if you want to retrieve all the data.