Fix check_exclusion_or_unique_constraint for UNIQUE NULLS NOT DISTINCT.

Adjusting this function was overlooked in commit 94aa7cc5f.  The only
visible symptom (so far) is that INSERT ... ON CONFLICT could go into
an endless loop when inserting a null that has a conflict.

Richard Guo and Tom Lane, per bug #17558 from Andrew Kesper

Discussion: https://postgr.es/m/17558-3f6599ffcf52fd4a@postgresql.org

3 files changed, 18 insertions, 10 deletions

diff --git a/src/backend/executor/execIndexing.c b/src/backend/executor/execIndexing.c
index 0cb0b8f1111..6a8735edf7f 100644
--- a/src/backend/executor/execIndexing.c
+++ b/src/backend/executor/execIndexing.c
@@ -699,13 +699,19 @@ check_exclusion_or_unique_constraint(Relation heap, Relation index,
 	}
 
 	/*
-	 * If any of the input values are NULL, the constraint check is assumed to
-	 * pass (i.e., we assume the operators are strict).
+	 * If any of the input values are NULL, and the index uses the default
+	 * nulls-are-distinct mode, the constraint check is assumed to pass (i.e.,
+	 * we assume the operators are strict).  Otherwise, we interpret the
+	 * constraint as specifying IS NULL for each column whose input value is
+	 * NULL.
 	 */
-	for (i = 0; i < indnkeyatts; i++)
+	if (!indexInfo->ii_NullsNotDistinct)
 	{
-		if (isnull[i])
-			return true;
+		for (i = 0; i < indnkeyatts; i++)
+		{
+			if (isnull[i])
+				return true;
+		}
 	}
 
 	/*
@@ -717,7 +723,7 @@ check_exclusion_or_unique_constraint(Relation heap, Relation index,
 	for (i = 0; i < indnkeyatts; i++)
 	{
 		ScanKeyEntryInitialize(&scankeys[i],
-							   0,
+							   isnull[i] ? SK_ISNULL | SK_SEARCHNULL : 0,
 							   i + 1,
 							   constr_strats[i],
 							   InvalidOid,
diff --git a/src/test/regress/expected/constraints.out b/src/test/regress/expected/constraints.out
index 36ccbb5f155..05b7244e4a7 100644
--- a/src/test/regress/expected/constraints.out
+++ b/src/test/regress/expected/constraints.out
@@ -449,15 +449,16 @@ DROP TABLE UNIQUE_TBL;
 CREATE TABLE UNIQUE_TBL (i int UNIQUE NULLS NOT DISTINCT, t text);
 INSERT INTO UNIQUE_TBL VALUES (1, 'one');
 INSERT INTO UNIQUE_TBL VALUES (2, 'two');
-INSERT INTO UNIQUE_TBL VALUES (1, 'three');
+INSERT INTO UNIQUE_TBL VALUES (1, 'three');  -- fail
 ERROR:  duplicate key value violates unique constraint "unique_tbl_i_key"
 DETAIL:  Key (i)=(1) already exists.
 INSERT INTO UNIQUE_TBL VALUES (4, 'four');
 INSERT INTO UNIQUE_TBL VALUES (5, 'one');
 INSERT INTO UNIQUE_TBL (t) VALUES ('six');
-INSERT INTO UNIQUE_TBL (t) VALUES ('seven');
+INSERT INTO UNIQUE_TBL (t) VALUES ('seven');  -- fail
 ERROR:  duplicate key value violates unique constraint "unique_tbl_i_key"
 DETAIL:  Key (i)=(null) already exists.
+INSERT INTO UNIQUE_TBL (t) VALUES ('eight') ON CONFLICT DO NOTHING;  -- no-op
 SELECT * FROM UNIQUE_TBL;
  i |  t   
 ---+------
diff --git a/src/test/regress/sql/constraints.sql b/src/test/regress/sql/constraints.sql
index 34de0c969ae..833819a32e2 100644
--- a/src/test/regress/sql/constraints.sql
+++ b/src/test/regress/sql/constraints.sql
@@ -310,11 +310,12 @@ CREATE TABLE UNIQUE_TBL (i int UNIQUE NULLS NOT DISTINCT, t text);
 
 INSERT INTO UNIQUE_TBL VALUES (1, 'one');
 INSERT INTO UNIQUE_TBL VALUES (2, 'two');
-INSERT INTO UNIQUE_TBL VALUES (1, 'three');
+INSERT INTO UNIQUE_TBL VALUES (1, 'three');  -- fail
 INSERT INTO UNIQUE_TBL VALUES (4, 'four');
 INSERT INTO UNIQUE_TBL VALUES (5, 'one');
 INSERT INTO UNIQUE_TBL (t) VALUES ('six');
-INSERT INTO UNIQUE_TBL (t) VALUES ('seven');
+INSERT INTO UNIQUE_TBL (t) VALUES ('seven');  -- fail
+INSERT INTO UNIQUE_TBL (t) VALUES ('eight') ON CONFLICT DO NOTHING;  -- no-op
 
 SELECT * FROM UNIQUE_TBL;