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

tglsfdc · tglsfdc · commit 4db84f088071 · 2005-02-11T00:41:12.000Z
Per gripes from Mike Mascari and Bernd Heller.
diff --git 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 */
 }

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.81 2005/01/27 23:23:53 neilc Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.82 2005/02/11 00:41:12 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*-------------------------------------------------------------------------`
`14`	`14`	`*/`
`@@ -1548,7 +1548,7 @@ compute_minimal_stats(VacAttrStatsP stats,`
`1548`	`1548`	`}`
`1549`	`1549`	`}`
`1550`	`1550`
`1551`		`- /* We can only compute valid stats if we found some non-null values. */`
	`1551`	`+ /* We can only compute real stats if we found some non-null values. */`
`1552`	`1552`	`if (nonnull_cnt > 0)`
`1553`	`1553`	`{`
`1554`	`1554`	`int nmultiple,`
`@@ -1705,6 +1705,17 @@ compute_minimal_stats(VacAttrStatsP stats,`
`1705`	`1705`	`stats->numvalues[0] = num_mcv;`
`1706`	`1706`	`}`
`1707`	`1707`	`}`
	`1708`	`+ else if (null_cnt > 0)`
	`1709`	`+ {`
	`1710`	`+ /* We found only nulls; assume the column is entirely null */`
	`1711`	`+ stats->stats_valid = true;`
	`1712`	`+ stats->stanullfrac = 1.0;`
	`1713`	`+ if (is_varwidth)`
	`1714`	`+ stats->stawidth = 0; /* "unknown" */`
	`1715`	`+ else`
	`1716`	`+ stats->stawidth = stats->attrtype->typlen;`
	`1717`	`+ stats->stadistinct = 0.0; /* "unknown" */`
	`1718`	`+ }`
`1708`	`1719`
`1709`	`1720`	`/* We don't need to bother cleaning up any of our temporary palloc's */`
`1710`	`1721`	`}`
`@@ -1812,7 +1823,7 @@ compute_scalar_stats(VacAttrStatsP stats,`
`1812`	`1823`	`values_cnt++;`
`1813`	`1824`	`}`
`1814`	`1825`
`1815`		`- /* We can only compute valid stats if we found some sortable values. */`
	`1826`	`+ /* We can only compute real stats if we found some sortable values. */`
`1816`	`1827`	`if (values_cnt > 0)`
`1817`	`1828`	`{`
`1818`	`1829`	`int ndistinct, /* # distinct values in sample */`
`@@ -2162,6 +2173,17 @@ compute_scalar_stats(VacAttrStatsP stats,`
`2162`	`2173`	`slot_idx++;`
`2163`	`2174`	`}`
`2164`	`2175`	`}`
	`2176`	`+ else if (nonnull_cnt == 0 && null_cnt > 0)`
	`2177`	`+ {`
	`2178`	`+ /* We found only nulls; assume the column is entirely null */`
	`2179`	`+ stats->stats_valid = true;`
	`2180`	`+ stats->stanullfrac = 1.0;`
	`2181`	`+ if (is_varwidth)`
	`2182`	`+ stats->stawidth = 0; /* "unknown" */`
	`2183`	`+ else`
	`2184`	`+ stats->stawidth = stats->attrtype->typlen;`
	`2185`	`+ stats->stadistinct = 0.0; /* "unknown" */`
	`2186`	`+ }`
`2165`	`2187`
`2166`	`2188`	`/* We don't need to bother cleaning up any of our temporary palloc's */`
`2167`	`2189`	`}`