Improve ALTER DOMAIN / DROP CONSTRAINT with nonexistent constraint

ALTER DOMAIN / DROP CONSTRAINT on a nonexistent constraint name did
not report any error.  Now it reports an error.  The IF EXISTS option
was added to get the usual behavior of ignoring nonexistent objects to
drop.

10 files changed, 45 insertions, 5 deletions

diff --git a/doc/src/sgml/ref/alter_domain.sgml b/doc/src/sgml/ref/alter_domain.sgml
index 29504ccd7c..2511a125d3 100644
--- a/doc/src/sgml/ref/alter_domain.sgml
+++ b/doc/src/sgml/ref/alter_domain.sgml
@@ -30,7 +30,7 @@ ALTER DOMAIN <replaceable class="PARAMETER">name</replaceable>
 ALTER DOMAIN <replaceable class="PARAMETER">name</replaceable>
     ADD <replaceable class="PARAMETER">domain_constraint</replaceable> [ NOT VALID ]
 ALTER DOMAIN <replaceable class="PARAMETER">name</replaceable>
-    DROP CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
+    DROP CONSTRAINT [ IF EXISTS ] <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
 ALTER DOMAIN <replaceable class="PARAMETER">name</replaceable>
     VALIDATE CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable>
 ALTER DOMAIN <replaceable class="PARAMETER">name</replaceable>
@@ -92,10 +92,12 @@ ALTER DOMAIN <replaceable class="PARAMETER">name</replaceable>
    </varlistentry>
 
    <varlistentry>
-    <term>DROP CONSTRAINT</term>
+    <term>DROP CONSTRAINT [ IF EXISTS ]</term>
     <listitem>
      <para>
       This form drops constraints on a domain.
+      If <literal>IF EXISTS</literal> is specified and the constraint
+      does not exist, no error is thrown. In this case a notice is issued instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 4bbbaf36c9..0f8af31fee 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -2264,7 +2264,7 @@ AlterDomainNotNull(List *names, bool notNull)
  */
 void
 AlterDomainDropConstraint(List *names, const char *constrName,
-						  DropBehavior behavior)
+						  DropBehavior behavior, bool missing_ok)
 {
 	TypeName   *typename;
 	Oid			domainoid;
@@ -2274,6 +2274,7 @@ AlterDomainDropConstraint(List *names, const char *constrName,
 	SysScanDesc conscan;
 	ScanKeyData key[1];
 	HeapTuple	contup;
+	bool		found = false;
 
 	/* Make a TypeName so we can use standard type lookup machinery */
 	typename = makeTypeNameFromNameList(names);
@@ -2317,6 +2318,7 @@ AlterDomainDropConstraint(List *names, const char *constrName,
 			conobj.objectSubId = 0;
 
 			performDeletion(&conobj, behavior);
+			found = true;
 		}
 	}
 	/* Clean up after the scan */
@@ -2324,6 +2326,19 @@ AlterDomainDropConstraint(List *names, const char *constrName,
 	heap_close(conrel, RowExclusiveLock);
 
 	heap_close(rel, NoLock);
+
+	if (!found)
+	{
+		if (!missing_ok)
+			ereport(ERROR,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+					 errmsg("constraint \"%s\" of domain \"%s\" does not exist",
+					   constrName, TypeNameToString(typename))));
+		else
+			ereport(NOTICE,
+					(errmsg("constraint \"%s\" of domain \"%s\" does not exist, skipping",
+							constrName, TypeNameToString(typename))));
+	}
 }
 
 /*
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index c9d3e2ee51..756e3a689b 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -2568,6 +2568,7 @@ _copyAlterDomainStmt(const AlterDomainStmt *from)
 	COPY_STRING_FIELD(name);
 	COPY_NODE_FIELD(def);
 	COPY_SCALAR_FIELD(behavior);
+	COPY_SCALAR_FIELD(missing_ok);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index efe2c96fea..9eff42f707 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1034,6 +1034,7 @@ _equalAlterDomainStmt(const AlterDomainStmt *a, const AlterDomainStmt *b)
 	COMPARE_STRING_FIELD(name);
 	COMPARE_NODE_FIELD(def);
 	COMPARE_SCALAR_FIELD(behavior);
+	COMPARE_SCALAR_FIELD(missing_ok);
 
 	return true;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 29df0c16b3..87d7305c76 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -7616,6 +7616,18 @@ AlterDomainStmt:
 					n->typeName = $3;
 					n->name = $6;
 					n->behavior = $7;
+					n->missing_ok = false;
+					$$ = (Node *)n;
+				}
+			/* ALTER DOMAIN <domain> DROP CONSTRAINT IF EXISTS <name> [RESTRICT|CASCADE] */
+			| ALTER DOMAIN_P any_name DROP CONSTRAINT IF_P EXISTS name opt_drop_behavior
+				{
+					AlterDomainStmt *n = makeNode(AlterDomainStmt);
+					n->subtype = 'X';
+					n->typeName = $3;
+					n->name = $8;
+					n->behavior = $9;
+					n->missing_ok = true;
 					$$ = (Node *)n;
 				}
 			/* ALTER DOMAIN <domain> VALIDATE CONSTRAINT <name> */
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 923da6a3f3..704bbe9ced 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -768,7 +768,8 @@ standard_ProcessUtility(Node *parsetree,
 					case 'X':	/* DROP CONSTRAINT */
 						AlterDomainDropConstraint(stmt->typeName,
 												  stmt->name,
-												  stmt->behavior);
+												  stmt->behavior,
+												  stmt->missing_ok);
 						break;
 					case 'V':	/* VALIDATE CONSTRAINT */
 						AlterDomainValidateConstraint(stmt->typeName,
diff --git a/src/include/commands/typecmds.h b/src/include/commands/typecmds.h
index 11d05b894f..3748bd56af 100644
--- a/src/include/commands/typecmds.h
+++ b/src/include/commands/typecmds.h
@@ -33,7 +33,7 @@ extern void AlterDomainNotNull(List *names, bool notNull);
 extern void AlterDomainAddConstraint(List *names, Node *constr);
 extern void AlterDomainValidateConstraint(List *names, char *constrName);
 extern void AlterDomainDropConstraint(List *names, const char *constrName,
-						  DropBehavior behavior);
+									  DropBehavior behavior, bool missing_ok);
 
 extern List *GetDomainConstraints(Oid typeOid);
 
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index bee0e1883f..0be3fb1174 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1264,6 +1264,7 @@ typedef struct AlterDomainStmt
 	char	   *name;			/* column or constraint name to act on */
 	Node	   *def;			/* definition of default or constraint */
 	DropBehavior behavior;		/* RESTRICT or CASCADE for DROP cases */
+	bool		missing_ok;		/* skip error if missing? */
 } AlterDomainStmt;
 
 
diff --git a/src/test/regress/expected/domain.out b/src/test/regress/expected/domain.out
index 3e44e3b533..4f47374b5d 100644
--- a/src/test/regress/expected/domain.out
+++ b/src/test/regress/expected/domain.out
@@ -358,6 +358,10 @@ alter domain con drop constraint t;
 insert into domcontest values (-5); --fails
 ERROR:  value for domain con violates check constraint "con_check"
 insert into domcontest values (42);
+alter domain con drop constraint nonexistent;
+ERROR:  constraint "nonexistent" of domain "con" does not exist
+alter domain con drop constraint if exists nonexistent;
+NOTICE:  constraint "nonexistent" of domain "con" does not exist, skipping
 -- Test ALTER DOMAIN .. CONSTRAINT .. NOT VALID
 create domain things AS INT;
 CREATE TABLE thethings (stuff things);
diff --git a/src/test/regress/sql/domain.sql b/src/test/regress/sql/domain.sql
index 1fd39008e6..ad049b7ba5 100644
--- a/src/test/regress/sql/domain.sql
+++ b/src/test/regress/sql/domain.sql
@@ -259,6 +259,9 @@ alter domain con drop constraint t;
 insert into domcontest values (-5); --fails
 insert into domcontest values (42);
 
+alter domain con drop constraint nonexistent;
+alter domain con drop constraint if exists nonexistent;
+
 -- Test ALTER DOMAIN .. CONSTRAINT .. NOT VALID
 create domain things AS INT;
 CREATE TABLE thethings (stuff things);