Drafting Queries Without a Table

Sometimes, we just want to try or demo a specific way to use SQL. Even if the query is simple, it can become a tedious task if it requires test data that is not yet available in any table. In such cases, the values statement can be handy.

In its full power, values can not only provide data to the insert statement, but be used as stand-alone statement very much like select. Unlike select, values doesn’t access any tables but only the data that is explicitly listed in the SQL statement.

The following example demonstrates that COUNT(*) and COUNT(expression) mean something different:0

SELECT COUNT(c1)
     , COUNT(*)
  FROM (VALUES (1)
             , (NULL)
       ) t1(c1)

The example uses the values clause to produce a table with two rows and one column (of unknown name). One of the values is null. To be able to refer to this column, and thus be able to apply an aggregate function upon it, the example aliases this derived table as t1 and its column as c1 using the alias columns in from syntax. Alternatively, you can use a with clause to name the columns. t1 and its columns can now be used like a regular table of view.

Compatibility

The example conforms to full SQL-92 and later standards with the optional features F641, F591 and F661.1

1. Only without keyword row
2. Requires keyword row: values row('r1c1','r1c2'), row('r2c1', 'r2c2')
3. Needs from clause column renaming • Only without keyword row
4. Requires column names in with clause • Only without keyword row
5. Only for values and select: FROM (VALUES | SELECT …) t(c1, c2)
6. Only for select: FROM (SELECT …) t(c1, c2)
7. Only for values, but then required: FROM (VALUES …) t(c1, c2)