Add special setting to show indexes.

src/Interpreters/InterpreterExplainQuery.cpp

@@ -129,6 +129,7 @@ struct QueryPlanSettings
             {"header", query_plan_options.header},
             {"description", query_plan_options.description},
             {"actions", query_plan_options.actions},
+            {"indexes", query_plan_options.indexes},
             {"optimize", optimize},
     };
 };

src/Processors/QueryPlan/IQueryPlanStep.h

@@ -99,6 +99,9 @@ public:
     /// Get detailed description of step actions. This is shown in EXPLAIN query with options `actions = 1`.
     virtual void describeActions(FormatSettings & /*settings*/) const {}
 
+    /// Get detailed description of read-from-storage step indexes (if any). Shown in with options `indexes = 1`.
+    virtual void describeIndexes(FormatSettings & /*settings*/) const {}
+
     /// Get description of processors added in current step. Should be called after updatePipeline().
     virtual void describePipeline(FormatSettings & /*settings*/) const {}
 

src/Processors/QueryPlan/QueryPlan.cpp

@@ -243,6 +243,9 @@ static void explainStep(
 
     if (options.actions)
         step.describeActions(settings);
+
+    if (options.indexes)
+        step.describeIndexes(settings);
 }
 
 std::string debugExplainStep(const IQueryPlanStep & step)

src/Processors/QueryPlan/QueryPlan.h

@@ -66,6 +66,8 @@ public:
         bool description = true;
         /// Add detailed information about step actions.
         bool actions = false;
+        /// Add information about indexes actions.
+        bool indexes = false;
     };
 
     struct ExplainPipelineOptions

src/Processors/QueryPlan/ReadFromMergeTree.cpp

@@ -191,6 +191,16 @@ void ReadFromMergeTree::describeActions(FormatSettings & format_settings) const
     std::string prefix(format_settings.offset, format_settings.indent_char);
     format_settings.out << prefix << "ReadType: " << readTypeToString(read_type) << '\n';
 
+    if (index_stats && !index_stats->empty())
+    {
+        format_settings.out << prefix << "Parts: " << index_stats->back().num_parts_after << '\n';
+        format_settings.out << prefix << "Granules: " << index_stats->back().num_granules_after << '\n';
+    }
+}
+
+void ReadFromMergeTree::describeIndexes(FormatSettings & format_settings) const
+{
+    std::string prefix(format_settings.offset, format_settings.indent_char);
     if (index_stats && !index_stats->empty())
     {
         std::string indent(format_settings.indent, format_settings.indent_char);
@@ -233,9 +243,6 @@ void ReadFromMergeTree::describeActions(FormatSettings & format_settings) const
                 format_settings.out << '/' << (*index_stats)[i - 1].num_granules_after;
             format_settings.out << '\n';
         }
-
-        format_settings.out << prefix << "Parts: " << index_stats->back().num_parts_after << '\n';
-        format_settings.out << prefix << "Granules: " << index_stats->back().num_granules_after << '\n';
     }
 }
 

src/Processors/QueryPlan/ReadFromMergeTree.h

@@ -85,6 +85,7 @@ public:
     void initializePipeline(QueryPipeline & pipeline, const BuildQueryPipelineSettings &) override;
 
     void describeActions(FormatSettings & format_settings) const override;
+    void describeIndexes(FormatSettings & format_settings) const override;
 
 private:
     const MergeTreeData & storage;

tests/queries/0_stateless/01786_explain_merge_tree.reference

@@ -1,5 +1,4 @@
       ReadFromMergeTree
-      ReadType: Default
       Indexes:
         MinMax
           Keys: 
@@ -31,45 +30,13 @@
           Description: set GRANULARITY 2
           Parts: 1/1
           Granules: 1/2
-      Parts: 1
-      Granules: 1
 -----------------
           ReadFromMergeTree
           ReadType: InOrder
-          Indexes:
-            MinMax
-              Description: true
-              Parts: 5/5
-              Granules: 12/12
-            Partition
-              Description: true
-              Parts: 5/5
-              Granules: 12/12
-            PrimaryKey
-              Keys: 
-                x
-              Description: (x in [16, +inf))
-              Parts: 1/5
-              Granules: 3/12
           Parts: 1
           Granules: 3
 -----------------
           ReadFromMergeTree
           ReadType: InReverseOrder
-          Indexes:
-            MinMax
-              Description: true
-              Parts: 5/5
-              Granules: 12/12
-            Partition
-              Description: true
-              Parts: 5/5
-              Granules: 12/12
-            PrimaryKey
-              Keys: 
-                x
-              Description: (x in [16, +inf))
-              Parts: 1/5
-              Granules: 3/12
           Parts: 1
           Granules: 3

tests/queries/0_stateless/01786_explain_merge_tree.sh

@@ -8,7 +8,7 @@ $CLICKHOUSE_CLIENT -q "create table test_index (x UInt32, y UInt32, z UInt32, t
 $CLICKHOUSE_CLIENT -q "insert into test_index select number, number > 3 ? 3 : number, number = 1 ? 1 : 0, number from numbers(20)"
 
 $CLICKHOUSE_CLIENT -q "
-    explain actions = 1 select *, _part from test_index where t % 19 = 16 and y > 0 and bitAnd(z, 3) != 1 and x > 10 and t % 20 > 14;
+    explain indexes = 1 select *, _part from test_index where t % 19 = 16 and y > 0 and bitAnd(z, 3) != 1 and x > 10 and t % 20 > 14;
     " | grep -A 100 "ReadFromMergeTree" # | grep -v "Description"
 
 echo "-----------------"