[Quan Zongliang <quanzongliang@yeah.net>]

I noticed that the subtype of AlterDomainStmt is directly using 
constants in the code. It is not conducive to the maintenance and 
reading of the code. Based on the definition of AlterTableType, use 
"AD_" as the prefix. Define several macros to replace the original 
characters.
The subtype of AlterTableCmd is defined using an enumeration. The 
subtypes of AlterDomainStmt are relatively few in number, and the 
original definition uses characters. These definitions still use 
characters and maintain the values unchanged. If some plugins or tools 
are also processing AlterDomainStmt, there will be no errors.

--
Quan Zongliang

Attachments:

alterdomain_subtype.patch (text/plain, 5.1K) download
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 54ad38247aa..3f09f85a480 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -15696,7 +15696,7 @@ ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId, char *cmd,
 		{
 			AlterDomainStmt *stmt = (AlterDomainStmt *) stm;
 
-			if (stmt->subtype == 'C')	/* ADD CONSTRAINT */
+			if (stmt->subtype == AD_AddConstraint)
 			{
 				Constraint *con = castNode(Constraint, stmt->def);
 				AlterTableCmd *cmd = makeNode(AlterTableCmd);
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 0b5652071d1..391e70b594c 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -11629,7 +11629,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'T';
+					n->subtype = AD_AlterDefault;
 					n->typeName = $3;
 					n->def = $4;
 					$$ = (Node *) n;
@@ -11639,7 +11639,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'N';
+					n->subtype = AD_DropNotNull;
 					n->typeName = $3;
 					$$ = (Node *) n;
 				}
@@ -11648,7 +11648,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'O';
+					n->subtype = AD_SetNotNull;
 					n->typeName = $3;
 					$$ = (Node *) n;
 				}
@@ -11657,7 +11657,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'C';
+					n->subtype = AD_AddConstraint;
 					n->typeName = $3;
 					n->def = $5;
 					$$ = (Node *) n;
@@ -11667,7 +11667,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'X';
+					n->subtype = AD_DropConstraint;
 					n->typeName = $3;
 					n->name = $6;
 					n->behavior = $7;
@@ -11679,7 +11679,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'X';
+					n->subtype = AD_DropConstraint;
 					n->typeName = $3;
 					n->name = $8;
 					n->behavior = $9;
@@ -11691,7 +11691,7 @@ AlterDomainStmt:
 				{
 					AlterDomainStmt *n = makeNode(AlterDomainStmt);
 
-					n->subtype = 'V';
+					n->subtype = AD_VaidateConstraint;
 					n->typeName = $3;
 					n->name = $6;
 					$$ = (Node *) n;
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 25fe3d58016..5c0a4eb53cb 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -1343,7 +1343,7 @@ ProcessUtilitySlow(ParseState *pstate,
 					 */
 					switch (stmt->subtype)
 					{
-						case 'T':	/* ALTER DOMAIN DEFAULT */
+						case AD_AlterDefault:
 
 							/*
 							 * Recursively alter column default for table and,
@@ -1353,30 +1353,30 @@ ProcessUtilitySlow(ParseState *pstate,
 								AlterDomainDefault(stmt->typeName,
 												   stmt->def);
 							break;
-						case 'N':	/* ALTER DOMAIN DROP NOT NULL */
+						case AD_DropNotNull:
 							address =
 								AlterDomainNotNull(stmt->typeName,
 												   false);
 							break;
-						case 'O':	/* ALTER DOMAIN SET NOT NULL */
+						case AD_SetNotNull:
 							address =
 								AlterDomainNotNull(stmt->typeName,
 												   true);
 							break;
-						case 'C':	/* ADD CONSTRAINT */
+						case AD_AddConstraint:
 							address =
 								AlterDomainAddConstraint(stmt->typeName,
 														 stmt->def,
 														 &secondaryObject);
 							break;
-						case 'X':	/* DROP CONSTRAINT */
+						case AD_DropConstraint:
 							address =
 								AlterDomainDropConstraint(stmt->typeName,
 														  stmt->name,
 														  stmt->behavior,
 														  stmt->missing_ok);
 							break;
-						case 'V':	/* VALIDATE CONSTRAINT */
+						case AD_VaidateConstraint:
 							address =
 								AlterDomainValidateConstraint(stmt->typeName,
 															  stmt->name);
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 4610fc61293..7349918e35e 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2534,14 +2534,7 @@ typedef struct AlterCollationStmt
 typedef struct AlterDomainStmt
 {
 	NodeTag		type;
-	char		subtype;		/*------------
-								 *	T = alter column default
-								 *	N = alter column drop not null
-								 *	O = alter column set not null
-								 *	C = add constraint
-								 *	X = drop constraint
-								 *------------
-								 */
+	char		subtype;		/* see AD_xxx constants below */
 	List	   *typeName;		/* domain to work on */
 	char	   *name;			/* column or constraint name to act on */
 	Node	   *def;			/* definition of default or constraint */
@@ -2549,6 +2542,13 @@ typedef struct AlterDomainStmt
 	bool		missing_ok;		/* skip error if missing? */
 } AlterDomainStmt;
 
+/* AlterDomainStmt action */
+#define AD_AlterDefault				'T'			/* SET|DROP DEFAULT */
+#define AD_DropNotNull				'N'			/* DROP NOT NULL */
+#define AD_SetNotNull				'O'			/* SET NOT NULL */
+#define AD_AddConstraint			'C'			/* ADD CONSTRAINT */
+#define AD_DropConstraint			'X'			/* DROP CONSTRAINT */
+#define AD_VaidateConstraint		'V'			/* VALIDATE CONSTRAINT */
 
 /* ----------------------
  *		Grant|Revoke Statement