1) Fix bug with LEFT JOIN ViewX and where clause with ViewX.FieldX IS NULL

2) When FIRST / SKIP is used in a sub-query it may not be affected by conjunctions in higher contexts.
  Example (should return 1 row instead of 5):
SELECT * FROM
  (SELECT FIRST 5 SKIP 2 cs.* FROM RDB$CHARACTER_SETS cs)
WHERE
  RDB$CHARACTER_SET_NAME starting with 'D'

src/jrd/opt.cpp

@@ -104,6 +104,7 @@ static USHORT distribute_equalities(LLS *, Csb*, USHORT);
 static bool dump_index(const jrd_nod*, SCHAR**, SSHORT*);
 static bool dump_rsb(const jrd_req*, const Rsb*, SCHAR**, SSHORT*);
 static bool estimate_cost(thread_db*, OPT, USHORT, double *, double *);
+static bool expression_contains(const jrd_nod*, NOD_T, bool, bool);
 #ifdef EXPRESSION_INDICES
 static bool expression_equal(thread_db*, jrd_nod*, jrd_nod*);
 #endif
@@ -180,7 +181,8 @@ static SSHORT sort_indices_by_priority(Csb::csb_repeat*, IDX **, UINT64 *);
 #define DEBUG_NONE		0
 
 IB_FILE *opt_debug_file = 0;
-static int opt_debug_flag = DEBUG_NONE;
+static int opt_debug_flag = DEBUG_RELATIONSHIPS;
+//static int opt_debug_flag = DEBUG_NONE;
 #endif
 
 inline void SET_DEP_BIT(ULONG* array, const SLONG bit)
@@ -364,7 +366,6 @@ Rsb* OPT_compile(thread_db* tdbb,
 	// put any additional booleans on the conjunct stack, and see if we 
 	// can generate additional booleans by associativity--this will help 
 	// to utilize indices that we might not have noticed
-
 	if (rse->rse_boolean) {
 		conjunct_count =
 			decompose(tdbb, rse->rse_boolean, &conjunct_stack, csb);
@@ -378,6 +379,13 @@ Rsb* OPT_compile(thread_db* tdbb,
 		stack_end = &(*stack_end)->lls_next;
 	}
 
+	// AB: If we have limit our retrieval with FIRST / SKIP syntax then
+	// we may not deliver above conditions (from higher rse's) to this 
+	// rse, because the results should be consistent.
+    if (rse->rse_skip || rse->rse_first) {
+		parent_stack = NULL;
+	}
+
 	// clear the csb_active flag of all streams in the rse
 	set_rse_inactive(csb, rse);
 
@@ -461,9 +469,40 @@ Rsb* OPT_compile(thread_db* tdbb,
 						csb->csb_rpt[outer_streams[i]].csb_flags |= csb_active;
 					}
 				}
+
+				lls** stackSavepoint = &conjunct_stack;
+				if (rse->rse_jointype != blr_inner) {
+					// Make list of nodes that can be delivered to a outer-stream.
+					// In fact this are all nodes except IS NULL (nod_missing).
+					// Note! That for OR nodes this meant the whole node must be ignored.
+					lls** stackItem = &parent_stack;
+					for (; *stackItem; stackItem = &(*stackItem)->lls_next) {
+						jrd_nod* deliverNode = (jrd_nod*) (*stackItem)->lls_object;
+						if (!expression_contains(deliverNode, nod_missing, true, true)) {
+							LLS_PUSH(deliverNode, &conjunct_stack);
+						}
+					}
+				}
+				else {
 					*stack_end = parent_stack;
+				}
+
 				rsb = OPT_compile(tdbb, csb, (RSE) node, conjunct_stack);
+
+				if (rse->rse_jointype != blr_inner) {
+					if (parent_stack) {
+						// Remove previously added parent conjuctions from the stack.
+						lls** stackItem = &conjunct_stack;
+						for (; stackSavepoint != stackItem; stackItem = &(*stackItem)->lls_next) {
+							LLS_POP(&conjunct_stack);
+						}
+					}
+				}
+				else {
 					*stack_end = NULL;
+				}
+
+
 				if (rse->rse_jointype == blr_left) {
 					for (SSHORT i = 1; i <= outer_streams[0]; i++) {
 						csb->csb_rpt[outer_streams[i]].csb_flags &= ~csb_active;
@@ -572,6 +611,7 @@ Rsb* OPT_compile(thread_db* tdbb,
 	for (stack_end = &conjunct_stack; *stack_end;
 		 stack_end = &(*stack_end)->lls_next);
 	const SLONG saved_conjunct_count = conjunct_count;
+
 	*stack_end = parent_stack;		
 	conjunct_count += distribute_equalities(&conjunct_stack, csb, conjunct_count);
 	if (parent_stack) {
@@ -2675,6 +2715,46 @@ static bool estimate_cost(thread_db* tdbb,
 }
 
 
+static bool expression_contains(const jrd_nod* node, NOD_T node_type, bool go_into_or, bool go_into_and)
+{
+/**************************************
+ *
+ *      e x p r e s s i o n _ c o n t a i n s
+ *
+ **************************************
+ *
+ * Functional description
+ *  Search if somewhere in the expression the give 
+ *  node_type is burried.
+ *
+ **************************************/
+	DEV_BLKCHK(node, type_nod);
+
+	if (!node) {
+		return false;
+	}
+
+	if (node->nod_type == node_type) {
+		return true;
+	}
+	else {
+
+		if (go_into_or && (node->nod_type == nod_or)) {
+			return expression_contains(node->nod_arg[0], node_type, go_into_or, go_into_and) ||
+				expression_contains(node->nod_arg[1], node_type, go_into_or, go_into_and);
+		}
+
+		if (go_into_and && (node->nod_type == nod_and)) {
+			return expression_contains(node->nod_arg[0], node_type, go_into_or, go_into_and) ||
+				expression_contains(node->nod_arg[1], node_type, go_into_or, go_into_and);
+		}
+
+		return false;
+	}
+
+}
+
+
 #ifdef EXPRESSION_INDICES
 static bool expression_equal(thread_db* tdbb, jrd_nod* node1, jrd_nod* node2)
 {