From 11dec10f9fc079ed74d623211e01f465e45d6a7c Mon Sep 17 00:00:00 2001
From: Dimitry Sibiryakov <sd@ibphoenix.com>
Date: Mon, 22 Jan 2024 15:41:36 +0100
Subject: [PATCH] Fix both parts of #7924 (#7940)

* Fix both parts of #7924

* STL-compatible empty() method used

* Get back to isEmpty()
---
 src/dsql/DdlNodes.epp | 12 ++++++++++++
 src/dsql/ddl.cpp      |  7 ++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/dsql/DdlNodes.epp b/src/dsql/DdlNodes.epp
index 0b3a4a67b3..e508f97ff1 100644
--- a/src/dsql/DdlNodes.epp
+++ b/src/dsql/DdlNodes.epp
@@ -8339,6 +8339,18 @@ void AlterRelationNode::modifyField(thread_db* tdbb, DsqlCompilerScratch* dsqlSc
 								FLD.RDB$SEGMENT_LENGTH.NULL, FLD.RDB$SEGMENT_LENGTH);
 						END_MODIFY
 
+						MODIFY RFR USING
+							if (field->explicitCollation)
+							{
+								RFR.RDB$COLLATION_ID.NULL = FALSE;
+								RFR.RDB$COLLATION_ID = field->collationId;
+							}
+							else
+							{
+								RFR.RDB$COLLATION_ID.NULL = TRUE;	// CORE-2426 and Issue #7924
+							}
+						END_MODIFY
+
 						newDom.dyn_fld_source = origDom.dyn_fld_source;
 					}
 					else	// Case b2: Domain -> internal domain.
diff --git a/src/dsql/ddl.cpp b/src/dsql/ddl.cpp
index d65d639789..761a13913b 100644
--- a/src/dsql/ddl.cpp
+++ b/src/dsql/ddl.cpp
@@ -276,8 +276,9 @@ void DDL_resolve_intl_type(DsqlCompilerScratch* dsqlScratch, dsql_fld* field,
 		return;
 	}
 
-	if (modifying)
+	if (modifying && field->charSet.isEmpty() && field->collate.isEmpty())
 	{
+		// Use charset and collation from already existing field if any
 		const dsql_fld* afield = field->fld_next;
 		USHORT bpc = 0;
 
@@ -310,10 +311,10 @@ void DDL_resolve_intl_type(DsqlCompilerScratch* dsqlScratch, dsql_fld* field,
 		}
 	}
 
-	if (!(field->charSet.hasData() || field->charSetId.has_value() ||	// set if a domain
+	if (!modifying && !(field->charSet.hasData() || field->charSetId.has_value() ||	// set if a domain
 		(field->flags & FLD_national)))
 	{
-		// Attach the database default character set, if not otherwise specified
+		// Attach the database default character set to the new field, if not otherwise specified
 
 		MetaName defaultCharSet;