Fix crash with multiIf and constant condition and nullable arguments

src/Interpreters/InterpreterSelectQuery.cpp

@@ -440,7 +440,6 @@ InterpreterSelectQuery::InterpreterSelectQuery(
     if (has_input || !joined_tables.resolveTables())
         joined_tables.makeFakeTable(storage, metadata_snapshot, source_header);
 
-
     if (context->getCurrentTransaction() && context->getSettingsRef().throw_on_unsupported_query_inside_transaction)
     {
         if (storage)

src/Interpreters/TreeOptimizer.cpp

@@ -703,8 +703,11 @@ void optimizeOrLikeChain(ASTPtr & query)
 
 }
 
-void TreeOptimizer::optimizeIf(ASTPtr & query, Aliases & aliases, bool if_chain_to_multiif)
+void TreeOptimizer::optimizeIf(ASTPtr & query, Aliases & aliases, bool if_chain_to_multiif, bool multiif_to_if)
 {
+    if (multiif_to_if)
+        optimizeMultiIfToIf(query);
+
     /// Optimize if with constant condition after constants was substituted instead of scalar subqueries.
     OptimizeIfWithConstantConditionVisitor(aliases).visit(query);
 
@@ -791,9 +794,6 @@ void TreeOptimizer::apply(ASTPtr & query, TreeRewriterResult & result,
     if (settings.optimize_normalize_count_variants)
         optimizeCountConstantAndSumOne(query, context);
 
-    if (settings.optimize_multiif_to_if)
-        optimizeMultiIfToIf(query);
-
     if (settings.optimize_rewrite_sum_if_to_count_if)
         optimizeSumIfFunctions(query);
 

src/Interpreters/TreeOptimizer.h

@@ -23,7 +23,7 @@ class TreeOptimizer
         const std::vector<TableWithColumnNamesAndTypes> & tables_with_columns,
         ContextPtr context);
 
-    static void optimizeIf(ASTPtr & query, Aliases & aliases, bool if_chain_to_multiif);
+    static void optimizeIf(ASTPtr & query, Aliases & aliases, bool if_chain_to_multiif, bool multiif_to_if);
     static void optimizeCountConstantAndSumOne(ASTPtr & query, ContextPtr context);
     static void optimizeGroupByFunctionKeys(ASTSelectQuery * select_query);
 };

src/Interpreters/TreeRewriter.cpp

@@ -1230,11 +1230,14 @@ TreeRewriterResultPtr TreeRewriter::analyzeSelect(
     /// Push the predicate expression down to subqueries. The optimization should be applied to both initial and secondary queries.
     result.rewrite_subqueries = PredicateExpressionsOptimizer(getContext(), tables_with_columns, settings).optimize(*select_query);
 
-    TreeOptimizer::optimizeIf(query, result.aliases, settings.optimize_if_chain_to_multiif);
+     /// Only apply AST optimization for initial queries.
+    const bool ast_optimizations_allowed =
+        getContext()->getClientInfo().query_kind != ClientInfo::QueryKind::SECONDARY_QUERY
+        && !select_options.ignore_ast_optimizations;
+
+    bool optimize_multiif_to_if = ast_optimizations_allowed && settings.optimize_multiif_to_if;
+    TreeOptimizer::optimizeIf(query, result.aliases, settings.optimize_if_chain_to_multiif, optimize_multiif_to_if);
 
-    /// Only apply AST optimization for initial queries.
-    const bool ast_optimizations_allowed
-        = getContext()->getClientInfo().query_kind != ClientInfo::QueryKind::SECONDARY_QUERY && !select_options.ignore_ast_optimizations;
     if (ast_optimizations_allowed)
         TreeOptimizer::apply(query, result, tables_with_columns, getContext());
 
@@ -1341,7 +1344,7 @@ TreeRewriterResultPtr TreeRewriter::analyze(
     if (settings.legacy_column_name_of_tuple_literal)
         markTupleLiteralsAsLegacy(query);
 
-    TreeOptimizer::optimizeIf(query, result.aliases, settings.optimize_if_chain_to_multiif);
+    TreeOptimizer::optimizeIf(query, result.aliases, settings.optimize_if_chain_to_multiif, false);
 
     if (allow_aggregations)
     {

tests/queries/0_stateless/02751_multiif_to_if_crash.reference

@@ -0,0 +1 @@
+1

tests/queries/0_stateless/02751_multiif_to_if_crash.sql

@@ -0,0 +1 @@
+SELECT sum(A) FROM (SELECT multiIf(1, 1, NULL) as A);