Fix ANALYZE to accumulate some minimal statistics for an all-null column.

Per gripes from Mike Mascari and Bernd Heller.

diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 45f8c234c1544c69f89b9c6c74f0f4bf5e40c753..ff20cf969671b7d00737ae1534dd7fc46e9a1609 100644 (file)
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.81 2005/01/27 23:23:53 neilc Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.82 2005/02/11 00:41:12 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1548,7 +1548,7 @@ compute_minimal_stats(VacAttrStatsP stats,
                }
        }
 
-       /* We can only compute valid stats if we found some non-null values. */
+       /* We can only compute real stats if we found some non-null values. */
        if (nonnull_cnt > 0)
        {
                int                     nmultiple,
@@ -1705,6 +1705,17 @@ compute_minimal_stats(VacAttrStatsP stats,
                        stats->numvalues[0] = num_mcv;
                }
        }
+       else if (null_cnt > 0)
+       {
+               /* We found only nulls; assume the column is entirely null */
+               stats->stats_valid = true;
+               stats->stanullfrac = 1.0;
+               if (is_varwidth)
+                       stats->stawidth = 0;                            /* "unknown" */
+               else
+                       stats->stawidth = stats->attrtype->typlen;
+               stats->stadistinct = 0.0;                               /* "unknown" */
+       }
 
        /* We don't need to bother cleaning up any of our temporary palloc's */
 }
@@ -1812,7 +1823,7 @@ compute_scalar_stats(VacAttrStatsP stats,
                values_cnt++;
        }
 
-       /* We can only compute valid stats if we found some sortable values. */
+       /* We can only compute real stats if we found some sortable values. */
        if (values_cnt > 0)
        {
                int                     ndistinct,      /* # distinct values in sample */
@@ -2162,6 +2173,17 @@ compute_scalar_stats(VacAttrStatsP stats,
                        slot_idx++;
                }
        }
+       else if (nonnull_cnt == 0 && null_cnt > 0)
+       {
+               /* We found only nulls; assume the column is entirely null */
+               stats->stats_valid = true;
+               stats->stanullfrac = 1.0;
+               if (is_varwidth)
+                       stats->stawidth = 0;                            /* "unknown" */
+               else
+                       stats->stawidth = stats->attrtype->typlen;
+               stats->stadistinct = 0.0;                               /* "unknown" */
+       }
 
        /* We don't need to bother cleaning up any of our temporary palloc's */
 }