In Microsoft Access, the SQL syntax of your query may say "Select Distinct" or "Select DistinctRow". Are you familiar with the difference? Learn how this impacts which records and number of records you see, and whether they can be edited.
When creating a query in Microsoft Access, you might want to return only distinct or unique values. There are two options in the query's property sheet, "Unique Values" and "Unique Records":
These properties correspond with the DISTINCT and DISTINCTROW statements (respectively) in SQL.
DISTINCT and DISTINCTROW sometimes provide the same results, but there are significant differences:
DISTINCT checks only the fields listed in the SQL string and then eliminates the duplicate rows. Results of DISTINCT queries are not updateable. They are a snapshot of the data.
DISTINCT queries are similar to Summary or Totals queries (queries using a GROUP BY clause).
DISTINCTROW, on the other hand, checks all fields in the table that is being queried, and eliminates duplicates based on the entire record (not just the selected fields). Results of DISTINCTROW queries are updateable.
Assume you have a simple orders database with the following data:
|2||Acme, Ltd.||New York|
|1||1||6/1||Total Access Analyzer|
|2||1||6/2||Total Access Statistics|
|3||2||6/3||Total Access Detective|
|4||3||6/3||Total Access Emailer|
You can see that ABC in London has 2 orders (CustID = 1), ABC in Paris has 1 order, and Acme has 1 order.
A simple SELECT query like this:
SELECT Company FROM Customers INNER JOIN Orders ON Customers.CustID = Orders.CustID;
returns one row for each Customer Order:
A SELECT DISTINCT query like this:
SELECT DISTINCT Company FROM Customers INNER JOIN Orders ON Customers.CustID = Orders.CustID;
limits the results to unique values in the output field. The query results are not updateable.
A SELECT DISTINCTROW query like this:
SELECT DISTINCTROW Company FROM Customers INNER JOIN Orders ON Customers.CustID = Orders.CustID;
looks at the entire underlying tables, not just the output fields, to find unique rows.
Here, you see both ABC, Inc. companies (the one in London and the one in Paris), even though the output fields match. The query results are updateable because they correspond to the individual records in the Customers table.
So to summarize, use DISTINCT if you need a snapshot of certain data, without seeing duplicates in the results. Use DISTINCTROW if you want to return entirely distinct records, regardless of what’s shown by the output.
Note that Microsoft SQL Server supports DISTINCT, but not DISTINCTROW.
If you plan to migrate to SQL Server, do not rely on DISTINCTROW queries.
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