Add IF NOT EXISTS for CREATE SERVER and CREATE USER MAPPING

There is still some inconsistency with the error messages surrounding
foreign servers. Some use the word "foreign" and some don't. My
inclination is to remove all such uses of "foreign" on the basis that
the  CREATE/ALTER/DROP SERVER commands don't use the word. However, that
is left for another day. In this patch I have kept to the existing usage
in the affected commands, which omits "foreign".

Anastasia Lubennikova, reviewed by Arthur Zakirov and Ashtosh Bapat.

Discussion: http://postgr.es/m/7c2ab9b8-388a-1ce0-23a3-7acf2a0ed3c6@postgrespro.ru

5 files changed, 67 insertions, 5 deletions

diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index 7f551149d2d..68100df0830 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -879,12 +879,25 @@ CreateForeignServer(CreateForeignServerStmt *stmt)
 
 	/*
 	 * Check that there is no other foreign server by this name.
+	 * Do nothing if IF NOT EXISTS was enforced.
 	 */
 	if (GetForeignServerByName(stmt->servername, true) != NULL)
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("server \"%s\" already exists",
-						stmt->servername)));
+	{
+		if (stmt->if_not_exists)
+		{
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("server \"%s\" already exists, skipping",
+							stmt->servername)));
+			heap_close(rel, RowExclusiveLock);
+			return InvalidObjectAddress;
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("server \"%s\" already exists",
+							stmt->servername)));
+	}
 
 	/*
 	 * Check that the FDW exists and that we have USAGE on it. Also get the
@@ -1152,12 +1165,27 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
 	umId = GetSysCacheOid2(USERMAPPINGUSERSERVER,
 						   ObjectIdGetDatum(useId),
 						   ObjectIdGetDatum(srv->serverid));
+
 	if (OidIsValid(umId))
-		ereport(ERROR,
+	{
+		if (stmt->if_not_exists)
+		{
+			ereport(NOTICE,
+				(errcode(ERRCODE_DUPLICATE_OBJECT),
+				 errmsg("user mapping for \"%s\" already exists for server %s, skipping",
+						MappingUserName(useId),
+						stmt->servername)));
+
+			heap_close(rel, RowExclusiveLock);
+			return InvalidObjectAddress;
+		}
+		else
+			ereport(ERROR,
 				(errcode(ERRCODE_DUPLICATE_OBJECT),
 				 errmsg("user mapping for \"%s\" already exists for server %s",
 						MappingUserName(useId),
 						stmt->servername)));
+	}
 
 	fdw = GetForeignDataWrapper(srv->fdwid);
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 6316688a883..d0d45a557b4 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4621,6 +4621,19 @@ CreateForeignServerStmt: CREATE SERVER name opt_type opt_foreign_server_version
 					n->version = $5;
 					n->fdwname = $9;
 					n->options = $10;
+					n->if_not_exists = false;
+					$$ = (Node *) n;
+				}
+				| CREATE SERVER IF_P NOT EXISTS name opt_type opt_foreign_server_version
+						 FOREIGN DATA_P WRAPPER name create_generic_options
+				{
+					CreateForeignServerStmt *n = makeNode(CreateForeignServerStmt);
+					n->servername = $6;
+					n->servertype = $7;
+					n->version = $8;
+					n->fdwname = $12;
+					n->options = $13;
+					n->if_not_exists = true;
 					$$ = (Node *) n;
 				}
 		;
@@ -4853,6 +4866,16 @@ CreateUserMappingStmt: CREATE USER MAPPING FOR auth_ident SERVER name create_gen
 					n->user = $5;
 					n->servername = $7;
 					n->options = $8;
+					n->if_not_exists = false;
+					$$ = (Node *) n;
+				}
+				| CREATE USER MAPPING IF_P NOT EXISTS FOR auth_ident SERVER name create_generic_options
+				{
+					CreateUserMappingStmt *n = makeNode(CreateUserMappingStmt);
+					n->user = $8;
+					n->servername = $10;
+					n->options = $11;
+					n->if_not_exists = true;
 					$$ = (Node *) n;
 				}
 		;
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index d576523f6a8..a15df229a49 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2154,6 +2154,7 @@ typedef struct CreateForeignServerStmt
 	char	   *servertype;		/* optional server type */
 	char	   *version;		/* optional server version */
 	char	   *fdwname;		/* FDW name */
+	bool		if_not_exists;	/* just do nothing if it already exists? */
 	List	   *options;		/* generic options to server */
 } CreateForeignServerStmt;
 
@@ -2188,6 +2189,7 @@ typedef struct CreateUserMappingStmt
 	NodeTag		type;
 	RoleSpec   *user;			/* user role */
 	char	   *servername;		/* server name */
+	bool		if_not_exists;	/* just do nothing if it already exists? */
 	List	   *options;		/* generic options to server */
 } CreateUserMappingStmt;
 
diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index 328366bcfc7..1c7a7593f9e 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -221,6 +221,10 @@ CREATE FOREIGN DATA WRAPPER foo;
 CREATE SERVER s1 FOREIGN DATA WRAPPER foo;
 COMMENT ON SERVER s1 IS 'foreign server';
 CREATE USER MAPPING FOR current_user SERVER s1;
+CREATE USER MAPPING FOR current_user SERVER s1;				-- ERROR
+ERROR:  user mapping for "regress_foreign_data_user" already exists for server s1
+CREATE USER MAPPING IF NOT EXISTS FOR current_user SERVER s1; -- NOTICE
+NOTICE:  user mapping for "regress_foreign_data_user" already exists for server s1, skipping
 \dew+
                                                 List of foreign-data wrappers
     Name    |           Owner           | Handler |        Validator         | Access privileges | FDW Options | Description 
@@ -284,6 +288,8 @@ CREATE FOREIGN DATA WRAPPER foo OPTIONS ("test wrapper" 'true');
 CREATE SERVER s1 FOREIGN DATA WRAPPER foo;
 CREATE SERVER s1 FOREIGN DATA WRAPPER foo;                  -- ERROR
 ERROR:  server "s1" already exists
+CREATE SERVER IF NOT EXISTS s1 FOREIGN DATA WRAPPER foo;	-- No ERROR, just NOTICE
+NOTICE:  server "s1" already exists, skipping
 CREATE SERVER s2 FOREIGN DATA WRAPPER foo OPTIONS (host 'a', dbname 'b');
 CREATE SERVER s3 TYPE 'oracle' FOREIGN DATA WRAPPER foo;
 CREATE SERVER s4 TYPE 'oracle' FOREIGN DATA WRAPPER foo OPTIONS (host 'a', dbname 'b');
diff --git a/src/test/regress/sql/foreign_data.sql b/src/test/regress/sql/foreign_data.sql
index c13d5ffbe92..aaf079cf525 100644
--- a/src/test/regress/sql/foreign_data.sql
+++ b/src/test/regress/sql/foreign_data.sql
@@ -104,6 +104,8 @@ CREATE FOREIGN DATA WRAPPER foo;
 CREATE SERVER s1 FOREIGN DATA WRAPPER foo;
 COMMENT ON SERVER s1 IS 'foreign server';
 CREATE USER MAPPING FOR current_user SERVER s1;
+CREATE USER MAPPING FOR current_user SERVER s1;				-- ERROR
+CREATE USER MAPPING IF NOT EXISTS FOR current_user SERVER s1; -- NOTICE
 \dew+
 \des+
 \deu+
@@ -121,6 +123,7 @@ CREATE SERVER s1 FOREIGN DATA WRAPPER foo;                  -- ERROR
 CREATE FOREIGN DATA WRAPPER foo OPTIONS ("test wrapper" 'true');
 CREATE SERVER s1 FOREIGN DATA WRAPPER foo;
 CREATE SERVER s1 FOREIGN DATA WRAPPER foo;                  -- ERROR
+CREATE SERVER IF NOT EXISTS s1 FOREIGN DATA WRAPPER foo;	-- No ERROR, just NOTICE
 CREATE SERVER s2 FOREIGN DATA WRAPPER foo OPTIONS (host 'a', dbname 'b');
 CREATE SERVER s3 TYPE 'oracle' FOREIGN DATA WRAPPER foo;
 CREATE SERVER s4 TYPE 'oracle' FOREIGN DATA WRAPPER foo OPTIONS (host 'a', dbname 'b');