Added actions setting for Explain query.

src/Interpreters/AggregateDescription.cpp

@@ -0,0 +1,80 @@
+#include <Interpreters/AggregateDescription.h>
+#include <Common/FieldVisitors.h>
+
+namespace DB
+{
+
+Strings AggregateDescription::explain() const
+{
+    Strings res;
+    String arguments_pos_str;
+    for (auto arg : arguments)
+    {
+        if (!arguments_pos_str.empty())
+            arguments_pos_str += ", ";
+
+        arguments_pos_str += std::to_string(arg);
+    }
+
+    if (arguments_pos_str.empty())
+        arguments_pos_str = "none";
+
+    res.emplace_back("argument positions: " + arguments_pos_str);
+
+    String arguments_names_str;
+    for (const auto & arg : argument_names)
+    {
+        if (!arguments_names_str.empty())
+            arguments_names_str += ", ";
+
+        arguments_names_str += arg;
+    }
+
+    if (arguments_names_str.empty())
+        arguments_names_str = "none";
+
+    res.emplace_back("arguments: " + arguments_names_str);
+    res.emplace_back("column_name: " + column_name);
+
+    auto get_params_string = [](const Array & arr)
+    {
+        String params_str;
+        for (const auto & param : arr)
+        {
+            if (!params_str.empty())
+                params_str += ", ";
+
+            params_str += applyVisitor(FieldVisitorToString(), param);
+        }
+
+        return params_str;
+    };
+
+    if (function)
+    {
+        String types_str;
+        for (const auto & type : function->getArgumentTypes())
+        {
+            if (!types_str.empty())
+                types_str += ", ";
+
+            types_str += type->getName();
+        }
+
+        auto params_str = get_params_string(function->getParameters());
+        if (!params_str.empty())
+            params_str = "(" + params_str + ")";
+
+        res.emplace_back("function: " + function->getName() + params_str + '(' + types_str + ") -> " +
+                         function->getReturnType()->getName());
+    }
+    else
+        res.emplace_back("function: nullptr");
+
+    if (!parameters.empty())
+        res.emplace_back("parameters: " + get_params_string(parameters));
+
+    return res;
+}
+
+}

src/Interpreters/AggregateDescription.h

@@ -15,6 +15,8 @@ struct AggregateDescription
     ColumnNumbers arguments;
     Names argument_names;    /// used if no `arguments` are specified.
     String column_name;      /// What name to use for a column with aggregate function values
+
+    Strings explain() const; /// Get description for EXPLAIN query.
 };
 
 using AggregateDescriptions = std::vector<AggregateDescription>;

src/Interpreters/Aggregator.cpp

@@ -150,6 +150,33 @@ Block Aggregator::Params::getHeader(
     return materializeBlock(res);
 }
 
+Strings Aggregator::Params::explain() const
+{
+    Strings res;
+    const auto & header = src_header ? src_header
+                                     : intermediate_header;
+    String keys_str;
+    for (auto key : keys)
+    {
+        if (keys_str.empty())
+            keys_str += ", ";
+
+        if (key >= header.columns())
+            keys_str += "unknown position " + std::to_string(key);
+        else
+            keys_str += src_header.getByPosition(key).name;
+    }
+
+    res.emplace_back("keys: " + std::move(keys_str));
+
+    for (const auto & aggregate : aggregates)
+    {
+        auto aggregate_strings = aggregate.explain();
+        res.insert(res.end(), aggregate_strings.begin(), aggregate_strings.end());
+    }
+
+    return res;
+}
 
 Aggregator::Aggregator(const Params & params_)
     : params(params_),

src/Interpreters/Aggregator.h

@@ -923,6 +923,9 @@ public:
         {
             return getHeader(src_header, intermediate_header, keys, aggregates, final);
         }
+
+        /// Returns keys and aggregated for EXPLAIN query
+        Strings explain() const;
     };
 
     Aggregator(const Params & params_);

src/Interpreters/InterpreterExplainQuery.cpp

@@ -120,6 +120,7 @@ struct ExplainSettings
     {
             {"header", query_plan_options.header},
             {"description", query_plan_options.description},
+            {"actions", query_plan_options.actions}
     };
 
     bool has(const std::string & name) const

src/Interpreters/ya.make

@@ -18,6 +18,7 @@ SRCS(
     ActionsVisitor.cpp
     addMissingDefaults.cpp
     addTypeConversionToAST.cpp
+    AggregateDescription.cpp
     Aggregator.cpp
     AnyInputOptimize.cpp
     ArithmeticOperationsInAgrFuncOptimize.cpp

src/Processors/QueryPlan/AggregatingStep.cpp

@@ -139,4 +139,9 @@ void AggregatingStep::transformPipeline(QueryPipeline & pipeline)
     pipeline.enableQuotaForCurrentStreams();
 }
 
+Strings AggregatingStep::describeActions() const
+{
+    return params.explain();
+}
+
 }

src/Processors/QueryPlan/AggregatingStep.h

@@ -28,6 +28,8 @@ public:
 
     void transformPipeline(QueryPipeline & pipeline) override;
 
+    Strings describeActions() const override;
+
 private:
     Aggregator::Params params;
     bool final;

src/Processors/QueryPlan/IQueryPlanStep.h

@@ -51,6 +51,9 @@ public:
     const std::string & getStepDescription() const { return step_description; }
     void setStepDescription(std::string description) { step_description = std::move(description); }
 
+    /// Get detailed description of step actions. This is shown in EXPLAIN query with options `actions = 1`.
+    virtual Strings describeActions() const { return {}; }
+
 protected:
     DataStreams input_streams;
     std::optional<DataStream> output_stream;

src/Processors/QueryPlan/QueryPlan.cpp

@@ -216,6 +216,25 @@ static void explainStep(
 
         buffer.write('\n');
     }
+
+    if (options.actions)
+    {
+        auto actions = step.describeActions();
+        if (!actions.empty())
+        {
+            buffer << "Actions: ";
+            bool first = true;
+
+            for (auto & action : actions)
+            {
+                if (!first)
+                    buffer << ",\n" << prefix << "         ";
+
+                first = false;
+                buffer << action;
+            }
+        }
+    }
 }
 
 void QueryPlan::explain(WriteBuffer & buffer, const ExplainOptions & options)

src/Processors/QueryPlan/QueryPlan.h

@@ -37,6 +37,7 @@ public:
     {
         bool header = false;
         bool description = true;
+        bool actions = false;
     };
 
     void explain(WriteBuffer & buffer, const ExplainOptions & options);