Collecting Statistics on Join Index Columns
For non-sparse join and hash indexes, the Optimizer inherits the row count and all
histograms from the base tables. Teradata recommends that you collect statistics on
base tables only and not on the non-sparse join or the hash indexes.
For sparse join indexes, Teradata recommends that you collect statistics on base tables
and sparse join indexes separately.
For non-compressed join indexes, the Optimizer performs all-AMP sampling to estimate
the join index row count accurately.
For compressed sparse join indexes, Teradata recommends that you collect PI statistics.
The All-AMP random sampling that the Optimizer performs may not reflect an accurate
row count because of the compression.