The general strategy in computing the Values function is to combine as many of the counts and measures for the various columns in as few Select statements as possible. Results from each Select statement are automatically placed in a temporary table; that is, each Select is actually an Insert-Select statement. The data for possibly multiple columns is then reorganized by way of Insert-Select statements that move each variable’s results one at a time into the final answer table. Note that distinct counts are performed separately and updated in the answer table in a final step. If the count of distinct values should fail, such as when a column is too wide, the count for that column can be set to null without affecting other results.
If requested, a Values analysis is performed on every requested column in the set of input tables. The measures provided include the count of non-null values, null values, unique values, blank values (character types only), and zero, positive and negative values (numeric types only).
The analysis parameter “Compute unique values for each column selected” must be selected in order for the unique values measure to be returned with a non-null value.