MDEV-6109: EXPLAIN JSON10.1-explain-json

- First code, "EXPLAIN FORMAT=JSON stmt" and "ANALYZE FORMAT=JSON stmt"
  work for basic queries.  Complex constructs (e.g subqueries, etc) not
  yet supported.
- No test infrastructure yet

1 files changed, 32 insertions, 11 deletions

diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index 42a3045cb1d..04892610fcf 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -97,6 +97,8 @@
 #include "log_slow.h"
 #include "sql_bootstrap.h"
 
+#include "my_json_writer.h" 
+
 #define FLAGSTR(V,F) ((V)&(F)?#F" ":"")
 
 #ifdef WITH_ARIA_STORAGE_ENGINE
@@ -5233,20 +5235,39 @@ static bool execute_sqlcom_select(THD *thd, TABLE_LIST *all_tables)
           top-level LIMIT
         */        
         result->reset_offset_limit(); 
-        thd->lex->explain->print_explain(result, thd->lex->describe,
-                                         thd->lex->analyze_stmt);
-        if (lex->describe & DESCRIBE_EXTENDED)
+        if (thd->lex->explain_json)
         {
-          char buff[1024];
-          String str(buff,(uint32) sizeof(buff), system_charset_info);
-          str.length(0);
           /*
-            The warnings system requires input in utf8, @see
-            mysqld_show_warnings().
+          Json_writer writer;
+          writer.start_object();
+          thd->lex->explain->print_explain_json(&writer, thd->lex->analyze_stmt);
+          writer.end_object();
+
+          const CHARSET_INFO *cs= system_charset_info;
+          List<Item> item_list;
+          String *buf= &writer.output;
+          item_list.push_back(new Item_string(buf->ptr(), buf->length(), cs));
+          result->send_data(item_list);
           */
-          thd->lex->unit.print(&str, QT_TO_SYSTEM_CHARSET);
-          push_warning(thd, Sql_condition::WARN_LEVEL_NOTE,
-                       ER_YES, str.c_ptr_safe());
+          thd->lex->explain->print_explain_json(result, thd->lex->analyze_stmt);
+        }
+        else
+        {
+          thd->lex->explain->print_explain(result, thd->lex->describe,
+                                           thd->lex->analyze_stmt);
+          if (lex->describe & DESCRIBE_EXTENDED)
+          {
+            char buff[1024];
+            String str(buff,(uint32) sizeof(buff), system_charset_info);
+            str.length(0);
+            /*
+              The warnings system requires input in utf8, @see
+              mysqld_show_warnings().
+            */
+            thd->lex->unit.print(&str, QT_TO_SYSTEM_CHARSET);
+            push_warning(thd, Sql_condition::WARN_LEVEL_NOTE,
+                         ER_YES, str.c_ptr_safe());
+          }
         }
       }