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
Related
I am trying to add a row in existing table I want to make it unique when I am trying to alter in phpmyadmin it says #1062 - Duplicate entry '0' for key 'mobile'
What code will help me suggest
This indicates that you have two entries which both have '0' in the mobile column. You can't force the column to be UNIQUE because there's non-unique data in their now. The solution is to resolve the conflict, but whether that's a good idea and how exactly to do so depends on your database design. The act of doing it is rather simple (just edit that row and assign a new value for 'mobile'), but depending on your design that could damage some data.
So without knowing the details, I can only caution you to not destroy any data or relations.
If you don't have a primary or unique key in that table, phpMyAdmin doesn't show the '"grid edit" feature, so if that's the case you can either write a little SQL to update the row directly, or temporarily add a new column, make it an autoincrementing primary key, do the edit through the phpMyAdmin interface, then remove the temporary autoincrement column (that's what I'd do; I just tested it and it took me about 30 seconds to add the column and key, edit a row, and delete the temporary column).
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.
I'm using MySQL Workbench to create a user table. I would like to make name and surname unique. On their own, name or surname are not unique as long as both are not duplicated simultaneously by a separate record.
Can I do this using MySQL Workbench or do I have to execute a a SQL statement manually? If so, what is the syntax?
So, there can be many name=John and surname=Doe but only 1 John Doe
In the tabs underneath the table design window, you'll see "Indexes". Click that tab, create a new unique index, tick the boxes for the columns you want to include in the unique index.
(The view you're looking at in your question is the "Columns" view, which lets you change details of individual columns, each of which can include a "unique" property, but for multi-column uniqueness you need to create an index.)
I am very new to database concepts and currently learning how to design a database. I have a table with below columns...
this is in mysql:
1. Names - text - unique but might change in future
2. Result - varchar - not unique
3. issues_id - int - not unique
4. comments - text - not unique
5. level - varchar - not unique
6. functionality - varchar - not unique
I cannot choose any of the above columns as primary keys as they might change in future. So i created a Auto-Increment id as names_id. I also have a GUI( a JTable) that shows this table and user updates Result,issues_id and comments based on the Names.Names here is a big text column. I cannot display names_id in the GUI as it does not make any sense in the GUI. Now when the user updates the database after giving inputs for column2,3,4 in the GUI i used the below query to update the database, i couldnt use names_id in where clause as the Jtable's row_id does not match with the names_id because not all the rows are loaded onto JTable.
update <tablename> set Result=<value>,issues_id=<value>,comments=<value>
where Names=<value>;
I could get the database updated but i want to know if its ok to update the database without even using the PK. how efficient is this? what purpose does the surrogate key serve here?
It is perfectly acceptable to update the database using a where condition that doesn't reference the primary key.
You may want to learn about indexes and constraints, though. You query could end up updating more than one row, if multiple rows have the same name. If you want to ensure that they are unique, then you can create a unique constraint on the column.
A primary key always creates an index on that column. This index makes access fast. If there is no index on name, then the update will need to scan the entire table to look at all names. You can make this faster by building an index on the field.
How do I create a unique combination constraint/index in MySQL? I do not mean a permutation. The order does not matter.
For example: I have two users that I want to match up together with a linking table. The table has nothing more than two columns which are both foreign keys corresponding to the primary key on the users table.
How do I create an index that will ensure that the pair remain unique in either order?
In your application enforce that col1 < col2 - this provides a consistent order and ensures only a single linking row will ever be generated. This does not mesh well with your preconditions ("in either order"), but it sounds like it should work for your situation. I ran into a similar problem before, before project requirements changed to asymmetric user relationships (a la Twitter).
as far as i understand your question. you want to add Unique Constraint combining two columns.
so try
ALTER TABLE `tableName` ADD UNIQUE (
`first_column` ,
`second_column`
);