dbms: More comments. Cleanups. Moved a lot of FunctionsArray code into implementation file. [#METR-19266]

dbms/include/DB/Functions/FunctionsConditional.h

@@ -15,9 +15,6 @@
 #include <DB/Functions/NumberTraits.h>
 #include <DB/Functions/DataTypeTraits.h>
 
-/// The following include is needed for the function multiIf.
-#include <DB/Functions/Conditional/CondException.h>
-
 namespace DB
 {
 
@@ -1458,6 +1455,12 @@ public:
 	}
 };
 
+namespace Conditional
+{
+
+class CondException;
+
+}
 
 /// Function multiIf, which generalizes the function if.
 ///
@@ -1471,6 +1474,9 @@ public:
 ///    - dates with time;
 ///    - strings;
 ///    - arrays of such types.
+///
+/// Additionally the arguments, conditions or branches, support nullable types
+/// and the NULL value.
 class FunctionMultiIf final : public IFunction
 {
 public:

dbms/src/Functions/FunctionsConditional.cpp

@@ -6,6 +6,7 @@
 #include <DB/Functions/Conditional/NumericPerformer.h>
 #include <DB/Functions/Conditional/StringEvaluator.h>
 #include <DB/Functions/Conditional/StringArrayEvaluator.h>
+#include <DB/Functions/Conditional/CondException.h>
 #include <DB/Columns/ColumnNullable.h>
 
 namespace DB

dbms/src/Functions/IFunction.cpp

@@ -11,6 +11,11 @@ namespace DB
 namespace
 {
 
+/// Suppose a function which has no special support for nullable arguments
+/// has been called with arguments, one or more of them being nullable.
+/// Then the method below endows the result, which is nullable, with a null
+/// byte map that is determined by OR-ing the null byte maps of the nullable
+/// arguments.
 void createNullValuesByteMap(Block & block, const ColumnNumbers & args, size_t result)
 {
 	ColumnNullable & res_col = static_cast<ColumnNullable &>(*block.unsafeGetByPosition(result).column);

dbms/src/Interpreters/ExpressionAnalyzer.cpp

@@ -255,7 +255,7 @@ void ExpressionAnalyzer::analyzeAggregation()
 		{
 			NameSet unique_keys;
 			ASTs & group_asts = select_query->group_expression_list->children;
-			for (ssize_t i = 0; i < group_asts.size(); ++i)
+			for (ssize_t i = 0; i < static_cast<ssize_t>(group_asts.size()); ++i)
 			{
 				size_t size = group_asts.size();
 				getRootActions(group_asts[i], true, false, temp_actions);
@@ -274,7 +274,7 @@ void ExpressionAnalyzer::analyzeAggregation()
 					/// But don't remove last key column if no aggregate functions, otherwise aggregation will not work.
 					if (!aggregate_descriptions.empty() || size > 1)
 					{
-						if (i + 1 < size)
+						if (i + 1 < static_cast<ssize_t>(size))
 							group_asts[i] = std::move(group_asts.back());
 
 						group_asts.pop_back();