From Stephan Szabo:

I believe this should fix the issue that Philip Warner
noticed about the check for unique constraints meeting the
referenced keys of a foreign key constraint allowing the
specification of a subset of a foreign key instead of
rejecting it.  I also added tests for a base case of
this to the foreign key and alter table tests and patches
for expected output.

src/test/regress/expected/alter_table.out

@@ -273,6 +273,9 @@ SELECT unique1 FROM tenk1 WHERE unique1 < 5;
 CREATE TABLE tmp2 (a int primary key);
 NOTICE:  CREATE TABLE/PRIMARY KEY will create implicit index 'tmp2_pkey' for table 'tmp2'
 CREATE TABLE tmp3 (a int, b int);
+CREATE TABLE tmp4 (a int, b int, unique(a,b));
+NOTICE:  CREATE TABLE/UNIQUE will create implicit index 'tmp4_a_key' for table 'tmp4'
+CREATE TABLE tmp5 (a int, b int);
 -- Insert rows into tmp2 (pktable)
 INSERT INTO tmp2 values (1);
 INSERT INTO tmp2 values (2);
@@ -299,6 +302,13 @@ DELETE FROM tmp3 where a=5;
 -- Try (and succeed)
 ALTER TABLE tmp3 add constraint tmpconstr foreign key (a) references tmp2 match full;
 NOTICE:  ALTER TABLE ... ADD CONSTRAINT will create implicit trigger(s) for FOREIGN KEY check(s)
+-- Try (and fail) to create constraint from tmp5(a) to tmp4(a) - unique constraint on
+-- tmp4 is a,b
+ALTER TABLE tmp5 add constraint tmpconstr foreign key(a) references tmp4(a) match full;
+NOTICE:  ALTER TABLE ... ADD CONSTRAINT will create implicit trigger(s) for FOREIGN KEY check(s)
+ERROR:  UNIQUE constraint matching given keys for referenced table "tmp4" not found
+DROP TABLE tmp5;
+DROP TABLE tmp4;
 DROP TABLE tmp3;
 NOTICE:  DROP TABLE implicitly drops referential integrity trigger from table "tmp2"
 NOTICE:  DROP TABLE implicitly drops referential integrity trigger from table "tmp2"

src/test/regress/expected/foreign_key.out

@@ -703,3 +703,12 @@ ERROR:  table "fktable_fail1" does not exist
 DROP TABLE FKTABLE_FAIL2;
 ERROR:  table "fktable_fail2" does not exist
 DROP TABLE PKTABLE;
+-- Test for referencing column number smaller than referenced constraint
+CREATE TABLE PKTABLE (ptest1 int, ptest2 int, UNIQUE(ptest1, ptest2));
+NOTICE:  CREATE TABLE/UNIQUE will create implicit index 'pktable_ptest1_key' for table 'pktable'
+CREATE TABLE FKTABLE_FAIL1 (ftest1 int REFERENCES pktable(ptest1));
+NOTICE:  CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
+ERROR:  UNIQUE constraint matching given keys for referenced table "pktable" not found
+DROP TABLE FKTABLE_FAIL1;
+ERROR:  table "fktable_fail1" does not exist
+DROP TABLE PKTABLE;

src/test/regress/sql/alter_table.sql

@@ -169,6 +169,10 @@ CREATE TABLE tmp2 (a int primary key);
 
 CREATE TABLE tmp3 (a int, b int);
 
+CREATE TABLE tmp4 (a int, b int, unique(a,b));
+
+CREATE TABLE tmp5 (a int, b int);
+
 -- Insert rows into tmp2 (pktable)
 INSERT INTO tmp2 values (1);
 INSERT INTO tmp2 values (2);
@@ -195,6 +199,15 @@ DELETE FROM tmp3 where a=5;
 -- Try (and succeed)
 ALTER TABLE tmp3 add constraint tmpconstr foreign key (a) references tmp2 match full;
 
+-- Try (and fail) to create constraint from tmp5(a) to tmp4(a) - unique constraint on
+-- tmp4 is a,b
+
+ALTER TABLE tmp5 add constraint tmpconstr foreign key(a) references tmp4(a) match full;
+
+DROP TABLE tmp5;
+
+DROP TABLE tmp4;
+
 DROP TABLE tmp3;
 
 DROP TABLE tmp2;

src/test/regress/sql/foreign_key.sql

@@ -418,3 +418,10 @@ CREATE TABLE FKTABLE_FAIL2 ( ftest1 int, CONSTRAINT fkfail1 FOREIGN KEY (ftest1)
 DROP TABLE FKTABLE_FAIL1;
 DROP TABLE FKTABLE_FAIL2;
 DROP TABLE PKTABLE;
+
+-- Test for referencing column number smaller than referenced constraint
+CREATE TABLE PKTABLE (ptest1 int, ptest2 int, UNIQUE(ptest1, ptest2));
+CREATE TABLE FKTABLE_FAIL1 (ftest1 int REFERENCES pktable(ptest1));
+
+DROP TABLE FKTABLE_FAIL1;
+DROP TABLE PKTABLE;