Microsoft Access 2010 Bible

Chapter 13: Accessing Data with VBA Code

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FIGURE 13.3

Setting the Unique Values property

Unique Values property

Top Values property

Unique Records property

Records returned by a query that includes the DISTINCT predicate are not updateable. Each

record in the result set represents one or more records in the underlying tables, and there is no

way for Access to know which records to update. Therefore, the data returned by a DISTINCT

query is read-only.

DISTINCTROW

The DISTINCTROW predicate is unique to Access. It works much like DISTINCT, with one big

difference: It looks for duplicates on the basis of all fields in the table(s) underlying the query, not

just the fields selected by the query.

Generally speaking, Access queries behave as if DISTINCTROW were always included in the SQL

statement. The only time you’ll see a query with DISTINCTROW return different records than a

query without DISTINCTROW is when all the tables underlying the query contain exactly the same

records. Because all the tables in a normalized database include a primary key that uniquely identi-

fies each row, it’s unlikely that a DISTINCTROW query will find identical records in tables joined

by a query.