do not rewrite count(if()) to countIf

Author: taiyang-li

src/Analyzer/Passes/RewriteAggregateFunctionWithIfPass.cpp

@@ -74,7 +74,13 @@ class RewriteAggregateFunctionWithIfVisitor : public InDepthQueryTreeVisitorWith
 
                 /// We need to preserve the output type from if()
                 if (if_arguments_nodes[1]->getResultType()->getName() != if_node->getResultType()->getName())
+                {
+                    /// For count, adding an extra cast is too heavy for the benefit.
+                    if (lower_name == "count")
+                        return;
+
                     new_arguments[0] = createCastFunction(std::move(if_arguments_nodes[1]), if_node->getResultType(), getContext());
+                }
                 else
                     new_arguments[0] = std::move(if_arguments_nodes[1]);
 
@@ -100,7 +106,13 @@ class RewriteAggregateFunctionWithIfVisitor : public InDepthQueryTreeVisitorWith
                 QueryTreeNodes new_arguments{2};
 
                 if (if_arguments_nodes[2]->getResultType()->getName() != if_node->getResultType()->getName())
+                {
+                    /// For count, adding an extra cast is too heavy for the benefit.
+                    if (lower_name == "count")
+                        return;
+
                     new_arguments[0] = createCastFunction(std::move(if_arguments_nodes[2]), if_node->getResultType(), getContext());
+                }
                 else
                     new_arguments[0] = std::move(if_arguments_nodes[2]);
 

tests/performance/rewrite_aggregate_if.xml

@@ -0,0 +1,4 @@
+<test>
+    <query>select count(if(rand() % 2 = 0, 1, null)) from numbers(100000000) settings optimize_rewrite_aggregate_function_with_if = true</query>
+    <query>select count(if(rand() % 2 = 0, null, 1)) from numbers(100000000) settings optimize_rewrite_aggregate_function_with_if = true</query>
+</test>