Postfix for #8062 - CREATE IF NOT EXISTS.

Thanks to Pavel Zotov.

doc/sql.extensions/README.ddl.txt

@@ -675,12 +675,16 @@ already exists.
 For ALTER TABLE ... ADD subclause, DDL triggers are not fired if there are only IF NOT EXISTS subclauses and all
 of them are related to existing columns or constraints.
 
-For others commands where IF NOT EXISTS is part of the main command, DDL triggers are not fired when the object
+For others commands (except users currently) where IF NOT EXISTS is part of the main command,
-already exists.
+DDL triggers are not fired when the object already exists.
 
 The engine only verifies if the name (object, column or constraint) already exists, and if yes, do nothing.
 It never tries to match the existing object with the one being created.
 
+Some objects share the same "namespace", for example, there cannot be a table and a procedure with the same name.
+In this case, if there is table XYZ and CREATE PROCEDURE IF NOT EXISTS XYZ is tried, the procedure will not be created
+and no error will be raised.
+
 The following statements are supported:
 
 CREATE EXCEPTION [IF NOT EXISTS] ...

src/dsql/DdlNodes.epp

@@ -1754,8 +1754,8 @@ void CreateAlterFunctionNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsql
 				status_exception::raise(Arg::Gds(isc_dyn_func_not_found) << Arg::Str(name));
 		}
 	}
-	else
+	else if (!executeCreate(tdbb, dsqlScratch, transaction))
-		executeCreate(tdbb, dsqlScratch, transaction);
+		return;
 
 	compile(tdbb, dsqlScratch);
 
@@ -1781,7 +1781,7 @@ void CreateAlterFunctionNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsql
 	}
 }
 
-void CreateAlterFunctionNode::executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch,
+bool CreateAlterFunctionNode::executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch,
 	jrd_tra* transaction)
 {
 	Attachment* const attachment = transaction->getAttachment();
@@ -1790,7 +1790,7 @@ void CreateAlterFunctionNode::executeCreate(thread_db* tdbb, DsqlCompilerScratch
 	if (package.isEmpty())
 	{
 		if (createIfNotExistsOnly && !DYN_UTIL_check_unique_name_nothrow(tdbb, transaction, name, obj_udf))
-			return;
+			return false;
 
 		executeDdlTrigger(tdbb, dsqlScratch, transaction, DTW_BEFORE,
 			DDL_TRIGGER_CREATE_FUNCTION, name, NULL);
@@ -1865,6 +1865,8 @@ void CreateAlterFunctionNode::executeCreate(thread_db* tdbb, DsqlCompilerScratch
 		storePrivileges(tdbb, transaction, name, obj_udf, EXEC_PRIVILEGES);
 
 	executeAlter(tdbb, dsqlScratch, transaction, false, false);
+
+	return true;
 }
 
 bool CreateAlterFunctionNode::executeAlter(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch,
@@ -2772,8 +2774,8 @@ void CreateAlterProcedureNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsq
 				status_exception::raise(Arg::Gds(isc_dyn_proc_not_found) << Arg::Str(name));
 		}
 	}
-	else
+	else if (!executeCreate(tdbb, dsqlScratch, transaction))
-		executeCreate(tdbb, dsqlScratch, transaction);
+		return;
 
 	compile(tdbb, dsqlScratch);
 
@@ -2799,7 +2801,7 @@ void CreateAlterProcedureNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsq
 	}
 }
 
-void CreateAlterProcedureNode::executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch,
+bool CreateAlterProcedureNode::executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch,
 	jrd_tra* transaction)
 {
 	Attachment* const attachment = transaction->getAttachment();
@@ -2808,7 +2810,7 @@ void CreateAlterProcedureNode::executeCreate(thread_db* tdbb, DsqlCompilerScratc
 	if (package.isEmpty())
 	{
 		if (createIfNotExistsOnly && !DYN_UTIL_check_unique_name_nothrow(tdbb, transaction, name, obj_procedure))
-			return;
+			return false;
 
 		executeDdlTrigger(tdbb, dsqlScratch, transaction, DTW_BEFORE,
 			DDL_TRIGGER_CREATE_PROCEDURE, name, NULL);
@@ -2875,6 +2877,8 @@ void CreateAlterProcedureNode::executeCreate(thread_db* tdbb, DsqlCompilerScratc
 		storePrivileges(tdbb, transaction, name, obj_procedure, EXEC_PRIVILEGES);
 
 	executeAlter(tdbb, dsqlScratch, transaction, false, false);
+
+	return true;
 }
 
 bool CreateAlterProcedureNode::executeAlter(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch,
@@ -6430,20 +6434,6 @@ void RelationNode::defineField(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch
 	dsql_fld* field = clause->field;
 	dsql_rel* relation = dsqlScratch->relation;
 
-	if (clause->createIfNotExistsOnly)
-	{
-		AutoCacheRequest request(tdbb, drq_l_rel_fld_name, DYN_REQUESTS);
-
-		FOR(REQUEST_HANDLE request TRANSACTION_HANDLE transaction)
-			RFL IN RDB$RELATION_FIELDS
-			WITH RFL.RDB$RELATION_NAME = relation->rel_name.c_str() AND
-				 RFL.RDB$FIELD_NAME = field->fld_name.c_str()
-		{
-			return;
-		}
-		END_FOR
-	}
-
 	// Add the field to the relation being defined for parsing purposes.
 
 	bool permanent = false;
@@ -6646,20 +6636,6 @@ void RelationNode::makeConstraint(thread_db* tdbb, DsqlCompilerScratch* dsqlScra
 {
 	MemoryPool& pool = dsqlScratch->getPool();
 
-	if (clause->createIfNotExistsOnly)
-	{
-		AutoCacheRequest request(tdbb, drq_l_rel_con, DYN_REQUESTS);
-
-		FOR(REQUEST_HANDLE request TRANSACTION_HANDLE transaction)
-			RC IN RDB$RELATION_CONSTRAINTS
-			WITH RC.RDB$CONSTRAINT_NAME EQ clause->name.c_str() AND
-				 RC.RDB$RELATION_NAME EQ name.c_str()
-		{
-			return;
-		}
-		END_FOR
-	}
-
 	switch (clause->constraintType)
 	{
 		case AddConstraintClause::CTYPE_NOT_NULL:
@@ -7754,10 +7730,33 @@ void AlterRelationNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsqlScratc
 			switch ((*i)->type)
 			{
 				case Clause::TYPE_ADD_COLUMN:
-					executeBeforeTrigger();
+				{
-					defineField(tdbb, dsqlScratch, transaction,
+					const auto addColumnClause = static_cast<AddColumnClause*>(i->getObject());
-						static_cast<AddColumnClause*>(i->getObject()), -1, NULL);
+					bool createColumn = true;
+
+					if (addColumnClause->createIfNotExistsOnly)
+					{
+						AutoCacheRequest request(tdbb, drq_l_rel_fld_name, DYN_REQUESTS);
+
+						FOR(REQUEST_HANDLE request TRANSACTION_HANDLE transaction)
+							RFL IN RDB$RELATION_FIELDS
+							WITH RFL.RDB$RELATION_NAME = relation->rel_name.c_str() AND
+								 RFL.RDB$FIELD_NAME = addColumnClause->field->fld_name.c_str()
+						{
+							createColumn = false;
+							break;
+						}
+						END_FOR
+					}
+
+					if (createColumn)
+					{
+						executeBeforeTrigger();
+						defineField(tdbb, dsqlScratch, transaction, addColumnClause, -1, nullptr);
+					}
+
 					break;
+				}
 
 				case Clause::TYPE_ALTER_COL_TYPE:
 					executeBeforeTrigger();
@@ -7937,16 +7936,46 @@ void AlterRelationNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsqlScratc
 				}
 
 				case Clause::TYPE_ADD_CONSTRAINT:
-					executeBeforeTrigger();
-					makeConstraint(tdbb, dsqlScratch, transaction,
-						static_cast<AddConstraintClause*>(i->getObject()), constraints);
-					break;
-
 				case Clause::TYPE_DROP_CONSTRAINT:
 				{
-					CreateDropConstraint& dropConstraint = constraints.add();
+					const bool silent = (*i)->type == Clause::TYPE_ADD_CONSTRAINT ?
-					dropConstraint.name = static_cast<const DropConstraintClause*>(i->getObject())->name;
+						static_cast<AddConstraintClause*>(i->getObject())->createIfNotExistsOnly :
-					dropConstraint.silent = static_cast<const DropConstraintClause*>(i->getObject())->silent;
+						static_cast<DropConstraintClause*>(i->getObject())->silent;
+					bool found = false;
+
+					if (silent)
+					{
+						const auto& constraintName = (*i)->type == Clause::TYPE_ADD_CONSTRAINT ?
+							static_cast<AddConstraintClause*>(i->getObject())->name :
+							static_cast<DropConstraintClause*>(i->getObject())->name;
+
+						AutoCacheRequest request(tdbb, drq_l_rel_con, DYN_REQUESTS);
+
+						FOR(REQUEST_HANDLE request TRANSACTION_HANDLE transaction)
+							RC IN RDB$RELATION_CONSTRAINTS
+							WITH RC.RDB$CONSTRAINT_NAME EQ constraintName.c_str() AND
+								 RC.RDB$RELATION_NAME EQ name.c_str()
+						{
+							found = true;
+							break;
+						}
+						END_FOR
+					}
+
+					if ((*i)->type == Clause::TYPE_ADD_CONSTRAINT && !(silent && found))
+					{
+						executeBeforeTrigger();
+						makeConstraint(tdbb, dsqlScratch, transaction,
+							static_cast<AddConstraintClause*>(i->getObject()), constraints);
+					}
+					else if ((*i)->type == Clause::TYPE_DROP_CONSTRAINT && !(silent && !found))
+					{
+						executeBeforeTrigger();
+						CreateDropConstraint& dropConstraint = constraints.add();
+						dropConstraint.name = static_cast<const DropConstraintClause*>(i->getObject())->name;
+						dropConstraint.silent = static_cast<const DropConstraintClause*>(i->getObject())->silent;
+					}
+
 					break;
 				}
 
@@ -8038,15 +8067,11 @@ void AlterRelationNode::execute(thread_db* tdbb, DsqlCompilerScratch* dsqlScratc
 						 RC.RDB$RELATION_NAME EQ name.c_str()
 				{
 					found = true;
-					executeBeforeTrigger();
 					ERASE RC;
 				}
 				END_FOR
 
-				if (!constraint->silent && !found)
+				if (!found)
-					executeBeforeTrigger();
-
-				if (!found && !constraint->silent)
 				{
 					// msg 130: "CONSTRAINT %s does not exist."
 					status_exception::raise(Arg::PrivateDyn(130) << constraint->name);

src/dsql/DdlNodes.h

@@ -459,7 +459,7 @@ private:
 		return external && external->udfModule.hasData();
 	}
 
-	void executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction);
+	bool executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction);
 	bool executeAlter(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction,
 		bool secondPass, bool runTriggers);
 	bool executeAlterIndividualParameters(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction,
@@ -599,7 +599,7 @@ protected:
 	}
 
 private:
-	void executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction);
+	bool executeCreate(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction);
 	bool executeAlter(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction,
 		bool secondPass, bool runTriggers);
 	bool executeAlterIndividualParameters(thread_db* tdbb, DsqlCompilerScratch* dsqlScratch, jrd_tra* transaction,