Cleanup: fake_select_lex->select_number=FAKE_SELECT_LEX_ID, not [U]INT_MAX

SELECT_LEX objects that are "fake_select_lex" (i.e read UNION output)
used both INT_MAX and UINT_MAX as select_number.
- mysql_explain_union() assigned UINT_MAX
- st_select_lex_unit::add_fake_select_lex assigned INT_MAX

This didn't matter initially (before EXPLAIN FORMAT=JSON), because the
code  had no checks for this value.

EXPLAIN FORMAT=JSON and later other features did introduce checks for
select_number values. The check had to check for two constants and
looked really confusing.

This patch joins the two constants into one - FAKE_SELECT_LEX_ID.

sql/my_json_writer.h

@@ -491,7 +491,7 @@ class Json_writer_object : public Json_writer_struct
     if (my_writer)
     {
       add_member("select_id");
-      if (unlikely(select_number >= INT_MAX))
+      if (unlikely(select_number == FAKE_SELECT_LEX_ID))
         context.add_str("fake");
       else
         context.add_ll(static_cast<longlong>(select_number));

sql/sql_explain.h

@@ -74,7 +74,7 @@ class Json_writer;
 *************************************************************************************/
 
 
-const int FAKE_SELECT_LEX_ID= (int)UINT_MAX;
+const uint FAKE_SELECT_LEX_ID= UINT_MAX;
 
 class Explain_query;
 
@@ -108,7 +108,7 @@ class Explain_node : public Sql_alloc
   };
 
   virtual enum explain_node_type get_type()= 0;
-  virtual int get_select_id()= 0;
+  virtual uint get_select_id()= 0;
 
   /**
     expression cache statistics
@@ -166,9 +166,9 @@ class Explain_basic_join : public Explain_node
 
   bool add_table(Explain_table_access *tab, Explain_query *query);
 
-  int get_select_id() { return select_id; }
+  uint get_select_id() { return select_id; }
 
-  int select_id;
+  uint select_id;
 
   int print_explain(Explain_query *query, select_result_sink *output,
                     uint8 explain_flags, bool is_analyze);
@@ -352,7 +352,7 @@ class Explain_union : public Explain_node
   enum explain_node_type get_type() { return EXPLAIN_UNION; }
   unit_common_op operation;
 
-  int get_select_id()
+  uint get_select_id()
   {
     DBUG_ASSERT(union_members.elements() > 0);
     return union_members.at(0);
@@ -879,7 +879,7 @@ class Explain_update : public Explain_node
   {}
 
   virtual enum explain_node_type get_type() { return EXPLAIN_UPDATE; }
-  virtual int get_select_id() { return 1; /* always root */ }
+  virtual uint get_select_id() { return 1; /* always root */ }
 
   const char *select_type;
 
@@ -959,7 +959,7 @@ class Explain_insert : public Explain_node
   StringBuffer<64> table_name;
 
   enum explain_node_type get_type() { return EXPLAIN_INSERT; }
-  int get_select_id() { return 1; /* always root */ }
+  uint get_select_id() { return 1; /* always root */ }
 
   int print_explain(Explain_query *query, select_result_sink *output, 
                     uint8 explain_flags, bool is_analyze);
@@ -986,7 +986,7 @@ class Explain_delete: public Explain_update
   bool deleting_all_rows;
 
   virtual enum explain_node_type get_type() { return EXPLAIN_DELETE; }
-  virtual int get_select_id() { return 1; /* always root */ }
+  virtual uint get_select_id() { return 1; /* always root */ }
 
   virtual int print_explain(Explain_query *query, select_result_sink *output, 
                             uint8 explain_flags, bool is_analyze);

sql/sql_parse.cc

@@ -8954,7 +8954,7 @@ bool st_select_lex_unit::add_fake_select_lex(THD *thd_arg)
       DBUG_RETURN(1);
   fake_select_lex->include_standalone(this, 
                                       (SELECT_LEX_NODE**)&fake_select_lex);
-  fake_select_lex->select_number= INT_MAX;
+  fake_select_lex->select_number= FAKE_SELECT_LEX_ID;
   fake_select_lex->parent_lex= thd_arg->lex; /* Used in init_query. */
   fake_select_lex->make_empty_select();
   fake_select_lex->set_linkage(GLOBAL_OPTIONS_TYPE);

sql/sql_select.cc

@@ -1585,7 +1585,7 @@ bool JOIN::build_explain()
   JOIN_TAB *curr_tab= join_tab + exec_join_tab_cnt();
   for (uint i= 0; i < aggr_tables; i++, curr_tab++)
   {
-    if (select_nr == INT_MAX)
+    if (select_nr == FAKE_SELECT_LEX_ID)
     {
       /* this is a fake_select_lex of a union */
       select_nr= select_lex->master_unit()->first_select()->select_number;
@@ -4208,14 +4208,12 @@ bool JOIN::save_explain_data(Explain_query *output, bool can_overwrite,
     If there is SELECT in this statement with the same number it must be the
     same SELECT
   */
-  DBUG_ASSERT(select_lex->select_number == UINT_MAX ||
-              select_lex->select_number == INT_MAX || !output ||
+  DBUG_ASSERT(select_lex->select_number == FAKE_SELECT_LEX_ID || !output ||
               !output->get_select(select_lex->select_number) ||
               output->get_select(select_lex->select_number)->select_lex ==
                 select_lex);
 
-  if (select_lex->select_number != UINT_MAX && 
-      select_lex->select_number != INT_MAX /* this is not a UNION's "fake select */ && 
+  if (select_lex->select_number != FAKE_SELECT_LEX_ID &&
       have_query_plan != JOIN::QEP_NOT_PRESENT_YET && 
       have_query_plan != JOIN::QEP_DELETED &&  // this happens when there was 
                                                // no QEP ever, but then
@@ -27780,8 +27778,7 @@ void st_select_lex::print(THD *thd, String *str, enum_query_type query_type)
   if ((query_type & QT_SHOW_SELECT_NUMBER) &&
       thd->lex->all_selects_list &&
       thd->lex->all_selects_list->link_next &&
-      select_number != UINT_MAX &&
-      select_number != INT_MAX)
+      select_number != FAKE_SELECT_LEX_ID)
   {
     str->append("/* select#");
     str->append_ulonglong(select_number);

sql/sql_tvc.cc

@@ -397,8 +397,7 @@ bool table_value_constr::optimize(THD *thd)
   create_explain_query_if_not_exists(thd->lex, thd->mem_root);
   have_query_plan= QEP_AVAILABLE;
 
-  if (select_lex->select_number != UINT_MAX &&
-      select_lex->select_number != INT_MAX /* this is not a UNION's "fake select */ &&
+  if (select_lex->select_number != FAKE_SELECT_LEX_ID &&
       have_query_plan != QEP_NOT_PRESENT_YET &&
       thd->lex->explain && // for "SET" command in SPs.
       (!thd->lex->explain->get_select(select_lex->select_number)))