Revise attribute handling code on partition creation

The original code to propagate NOT NULL and default expressions
specified when creating a partition was mostly copy-pasted from
typed-tables creation, but not being a great match it contained some
duplicity, inefficiency and bugs.

This commit fixes the bug that NOT NULL constraints declared in the
parent table would not be honored in the partition.  One reported issue
that is not fixed is that a DEFAULT declared in the child is not used
when inserting through the parent.  That would amount to a behavioral
change that's better not back-patched.

This rewrite makes the code simpler:

1. instead of checking for duplicate column names in its own block,
reuse the original one that already did that;

2. instead of concatenating the list of columns from parent and the one
declared in the partition and scanning the result to (incorrectly)
propagate defaults and not-null constraints, just scan the latter
searching the former for a match, and merging sensibly.  This works
because we know the list in the parent is already correct and there can
only be one parent.

This rewrite makes ColumnDef->is_from_parent unused, so it's removed
on branch master; on released branches, it's kept as an unused field in
order not to cause ABI incompatibilities.

This commit also adds a test case for creating partitions with
collations mismatching that on the parent table, something that is
closely related to the code being patched.  No code change is introduced
though, since that'd be a behavior change that could break some (broken)
working applications.

Amit Langote wrote a less invasive fix for the original
NOT NULL/defaults bug, but while I kept the tests he added, I ended up
not using his original code.  Ashutosh Bapat reviewed Amit's fix.  Amit
reviewed mine.

Author: Álvaro Herrera, Amit Langote
Reviewed-by: Ashutosh Bapat, Amit Langote
Reported-by: Jürgen Strobel (bug #15212)
Discussion: https://postgr.es/m/152746742177.1291.9847032632907407358@wrigleys.postgresql.org

1 files changed, 46 insertions, 53 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 6048334c755..a0279ae3838 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1893,17 +1893,6 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 						MaxHeapAttributeNumber)));
 
 	/*
-	 * In case of a partition, there are no new column definitions, only dummy
-	 * ColumnDefs created for column constraints.  We merge them with the
-	 * constraints inherited from the parent.
-	 */
-	if (is_partition)
-	{
-		saved_schema = schema;
-		schema = NIL;
-	}
-
-	/*
 	 * Check for duplicate names in the explicit list of attributes.
 	 *
 	 * Although we might consider merging such entries in the same way that we
@@ -1916,17 +1905,19 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 		ListCell   *rest = lnext(entry);
 		ListCell   *prev = entry;
 
-		if (coldef->typeName == NULL)
-
+		if (!is_partition && coldef->typeName == NULL)
+		{
 			/*
 			 * Typed table column option that does not belong to a column from
 			 * the type.  This works because the columns from the type come
-			 * first in the list.
+			 * first in the list.  (We omit this check for partition column
+			 * lists; those are processed separately below.)
 			 */
 			ereport(ERROR,
 					(errcode(ERRCODE_UNDEFINED_COLUMN),
 					 errmsg("column \"%s\" does not exist",
 							coldef->colname)));
+		}
 
 		while (rest != NULL)
 		{
@@ -1960,6 +1951,17 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 	}
 
 	/*
+	 * In case of a partition, there are no new column definitions, only dummy
+	 * ColumnDefs created for column constraints.  Set them aside for now and
+	 * process them at the end.
+	 */
+	if (is_partition)
+	{
+		saved_schema = schema;
+		schema = NIL;
+	}
+
+	/*
 	 * Scan the parents left-to-right, and merge their attributes to form a
 	 * list of inherited attributes (inhSchema).  Also check to see if we need
 	 * to inherit an OID column.
@@ -2175,7 +2177,6 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 				def->is_local = false;
 				def->is_not_null = attribute->attnotnull;
 				def->is_from_type = false;
-				def->is_from_parent = true;
 				def->storage = attribute->attstorage;
 				def->raw_default = NULL;
 				def->cooked_default = NULL;
@@ -2428,59 +2429,51 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 	/*
 	 * Now that we have the column definition list for a partition, we can
 	 * check whether the columns referenced in the column constraint specs
-	 * actually exist.  Also, we merge the constraints into the corresponding
-	 * column definitions.
+	 * actually exist.  Also, we merge NOT NULL and defaults into each
+	 * corresponding column definition.
 	 */
-	if (is_partition && list_length(saved_schema) > 0)
+	if (is_partition)
 	{
-		schema = list_concat(schema, saved_schema);
-
-		foreach(entry, schema)
+		foreach(entry, saved_schema)
 		{
-			ColumnDef  *coldef = lfirst(entry);
-			ListCell   *rest = lnext(entry);
-			ListCell   *prev = entry;
+			ColumnDef  *restdef = lfirst(entry);
+			bool		found = false;
+			ListCell   *l;
 
-			/*
-			 * Partition column option that does not belong to a column from
-			 * the parent.  This works because the columns from the parent
-			 * come first in the list (see above).
-			 */
-			if (coldef->typeName == NULL)
-				ereport(ERROR,
-						(errcode(ERRCODE_UNDEFINED_COLUMN),
-						 errmsg("column \"%s\" does not exist",
-								coldef->colname)));
-			while (rest != NULL)
+			foreach(l, schema)
 			{
-				ColumnDef  *restdef = lfirst(rest);
-				ListCell   *next = lnext(rest); /* need to save it in case we
-												 * delete it */
+				ColumnDef  *coldef = lfirst(l);
 
 				if (strcmp(coldef->colname, restdef->colname) == 0)
 				{
+					found = true;
+					coldef->is_not_null |= restdef->is_not_null;
+
 					/*
-					 * merge the column options into the column from the
-					 * parent
+					 * Override the parent's default value for this column
+					 * (coldef->cooked_default) with the partition's local
+					 * definition (restdef->raw_default), if there's one. It
+					 * should be physically impossible to get a cooked default
+					 * in the local definition or a raw default in the
+					 * inherited definition, but make sure they're nulls, for
+					 * future-proofing.
 					 */
-					if (coldef->is_from_parent)
+					Assert(restdef->cooked_default == NULL);
+					Assert(coldef->raw_default == NULL);
+					if (restdef->raw_default)
 					{
-						coldef->is_not_null = restdef->is_not_null;
 						coldef->raw_default = restdef->raw_default;
-						coldef->cooked_default = restdef->cooked_default;
-						coldef->constraints = restdef->constraints;
-						coldef->is_from_parent = false;
-						list_delete_cell(schema, rest, prev);
+						coldef->cooked_default = NULL;
 					}
-					else
-						ereport(ERROR,
-								(errcode(ERRCODE_DUPLICATE_COLUMN),
-								 errmsg("column \"%s\" specified more than once",
-										coldef->colname)));
 				}
-				prev = rest;
-				rest = next;
 			}
+
+			/* complain for constraints on columns not in parent */
+			if (!found)
+				ereport(ERROR,
+						(errcode(ERRCODE_UNDEFINED_COLUMN),
+						 errmsg("column \"%s\" does not exist",
+								restdef->colname)));
 		}
 	}