MDEV-33971 NAME_CONST in WHERE clause replaced by inner item

Improve performance of queries like
  SELECT * FROM t1 WHERE field = NAME_CONST('a', 4);
by, in this example, replacing the WHERE clause with field = 4
in the case of ref access.

The rewrite is done during fix_fields and we disambiguate this
case from other cases of NAME_CONST by inspecting where we are
in parsing.  We rely on THD::where to accomplish this.  To
improve performance there, we change the type of THD::where to
be an enumeration, so we can avoid string comparisons during
Item_name_const::fix_fields.  Consequently, this patch also
changes all usages of THD::where to conform likewise.

mysql-test/main/fulltext_order_by.result

@@ -126,7 +126,7 @@ group by
 a.text, b.id, b.betreff
 order by 
 match(b.betreff) against ('+abc' in boolean mode) desc;
-ERROR 42000: Table 'b' from one of the SELECTs cannot be used in ORDER clause
+ERROR 42000: Table 'b' from one of the SELECTs cannot be used in order clause
 select a.text, b.id, b.betreff
 from 
 t2 a inner join t3 b on a.id = b.forum inner join
@@ -142,7 +142,7 @@ where
 match(c.beitrag) against ('+abc' in boolean mode)
 order by 
 match(b.betreff) against ('+abc' in boolean mode) desc;
-ERROR 42000: Table 'b' from one of the SELECTs cannot be used in ORDER clause
+ERROR 42000: Table 'b' from one of the SELECTs cannot be used in order clause
 select a.text, b.id, b.betreff
 from 
 t2 a inner join t3 b on a.id = b.forum inner join

mysql-test/main/union.result

@@ -80,7 +80,7 @@ a b
 2 b
 1 a
 (select a,b from t1 limit 2) union all (select a,b from t2 order by a limit 1) order by t1.b;
-ERROR 42000: Table 't1' from one of the SELECTs cannot be used in ORDER clause
+ERROR 42000: Table 't1' from one of the SELECTs cannot be used in order clause
 explain extended (select a,b from t1 limit 2) union all (select a,b from t2 order by a limit 1) order by b desc;
 id select_type table type possible_keys key key_len ref rows filtered Extra
 1 PRIMARY t1 ALL NULL NULL NULL NULL 4 100.00 
@@ -493,7 +493,7 @@ drop temporary table t1;
 create table t1 select a from t1 union select a from t2;
 ERROR 42S01: Table 't1' already exists
 select a from t1 union select a from t2 order by t2.a;
-ERROR 42000: Table 't2' from one of the SELECTs cannot be used in ORDER clause
+ERROR 42000: Table 't2' from one of the SELECTs cannot be used in order clause
 drop table t1,t2;
 select length(version()) > 1 as `*` UNION select 2;
 *

mysql-test/suite/innodb_fts/r/fulltext_order_by.result

@@ -129,7 +129,7 @@ group by
 a.text, b.id, b.betreff
 order by 
 match(b.betreff) against ('+abc' in boolean mode) desc;
-ERROR 42000: Table 'b' from one of the SELECTs cannot be used in ORDER clause
+ERROR 42000: Table 'b' from one of the SELECTs cannot be used in order clause
 select a.text, b.id, b.betreff
 from 
 t2 a inner join t3 b on a.id = b.forum inner join
@@ -145,7 +145,7 @@ where
 match(c.beitrag) against ('+abc' in boolean mode)
 order by 
 match(b.betreff) against ('+abc' in boolean mode) desc;
-ERROR 42000: Table 'b' from one of the SELECTs cannot be used in ORDER clause
+ERROR 42000: Table 'b' from one of the SELECTs cannot be used in order clause
 select a.text, b.id, b.betreff
 from 
 t2 a inner join t3 b on a.id = b.forum inner join

sql/item.cc

@@ -2176,6 +2176,11 @@ Item::Type Item_name_const::type() const
 
 bool Item_name_const::fix_fields(THD *thd, Item **ref)
 {
+ if (thd->where == THD_WHERE::WHERE_CLAUSE) {
+ value_item->fix_fields_if_needed(thd, &value_item);
+ thd->change_item_tree(ref, value_item);
+ return FALSE;
+ }
  if (value_item->fix_fields_if_needed(thd, &value_item) ||
  name_item->fix_fields_if_needed(thd, &name_item) ||
  !value_item->const_item() ||
@@ -5528,7 +5533,7 @@ static Item** find_field_in_group_list(Item *find_item, ORDER *group_list)
  is ambiguous.
  */
  my_error(ER_NON_UNIQ_ERROR, MYF(0),
- find_item->full_name(), current_thd->where);
+ find_item->full_name(), thd_where(current_thd));
  return NULL;
  }
  }
@@ -5613,7 +5618,7 @@ resolve_ref_in_select_and_group(THD *thd, Item_ident *ref, SELECT_LEX *select)
  push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
  ER_NON_UNIQ_ERROR,
  ER_THD(thd,ER_NON_UNIQ_ERROR), ref->full_name(),
- thd->where);
+ thd_where(thd));
 
  }
  }
@@ -5947,7 +5952,7 @@ Item_field::fix_outer_field(THD *thd, Field **from_field, Item **reference)
  if (upward_lookup)
  {
  // We can't say exactly what absent table or field
- my_error(ER_BAD_FIELD_ERROR, MYF(0), full_name(), thd->where);
+ my_error(ER_BAD_FIELD_ERROR, MYF(0), full_name(), thd_where(thd));
  }
  else
  {
@@ -6174,7 +6179,7 @@ bool Item_field::fix_fields(THD *thd, Item **reference)
  {
  /* The column to which we link isn't valid. */
  my_error(ER_BAD_FIELD_ERROR, MYF(0), (*res)->name.str,
- thd->where);
+ thd_where(thd));
  return(1);
  }
 
@@ -6219,7 +6224,7 @@ bool Item_field::fix_fields(THD *thd, Item **reference)
 
  if (unlikely(!select))
  {
- my_error(ER_BAD_FIELD_ERROR, MYF(0), full_name(), thd->where);
+ my_error(ER_BAD_FIELD_ERROR, MYF(0), full_name(), thd_where(thd));
  goto error;
  }
  if ((ret= fix_outer_field(thd, &from_field, reference)) < 0)
@@ -8163,7 +8168,7 @@ bool Item_ref::fix_fields(THD *thd, Item **reference)
  if (unlikely(!outer_context))
  {
  /* The current reference cannot be resolved in this query. */
- my_error(ER_BAD_FIELD_ERROR,MYF(0), full_name(), thd->where);
+ my_error(ER_BAD_FIELD_ERROR,MYF(0), full_name(), thd_where(thd));
  goto error;
  }
 
@@ -8314,7 +8319,7 @@ bool Item_ref::fix_fields(THD *thd, Item **reference)
  {
  /* The item was not a table field and not a reference */
  my_error(ER_BAD_FIELD_ERROR, MYF(0),
- this->full_name(), thd->where);
+ this->full_name(), thd_where(thd));
  goto error;
  }
  /* Should be checked in resolve_ref_in_select_and_group(). */

sql/item_subselect.cc

@@ -241,7 +241,7 @@ Item_subselect::select_transformer(JOIN *join)
 
 bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
 {
- char const *save_where= thd_param->where;
+ THD_WHERE save_where= thd_param->where;
  uint8 uncacheable;
  bool res;
 
@@ -320,7 +320,7 @@ bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
  if (have_to_be_excluded)
  engine->exclude();
  substitution= 0;
- thd->where= "checking transformed subquery";
+ thd->where= THD_WHERE::CHECKING_TRANSFORMED_SUBQUERY;
  res= (*ref)->fix_fields_if_needed(thd, ref);
  goto end;
 
@@ -3403,13 +3403,13 @@ Item_in_subselect::select_in_like_transformer(JOIN *join)
 {
  Query_arena *arena= 0, backup;
  SELECT_LEX *current= thd->lex->current_select;
- const char *save_where= thd->where;
+ THD_WHERE save_where= thd->where;
  bool trans_res= true;
  bool result;
 
  DBUG_ENTER("Item_in_subselect::select_in_like_transformer");
  DBUG_ASSERT(thd == join->thd);
- thd->where= "IN/ALL/ANY subquery";
+ thd->where= THD_WHERE::IN_ALL_ANY_SUBQUERY;
 
  /*
  In some optimisation cases we will not need this Item_in_optimizer
@@ -3496,7 +3496,7 @@ bool Item_in_subselect::fix_fields(THD *thd_arg, Item **ref)
 {
  uint outer_cols_num;
  List<Item> *inner_cols;
- char const *save_where= thd_arg->where;
+ THD_WHERE save_where= thd_arg->where;
  DBUG_ENTER("Item_in_subselect::fix_fields");
 
  thd= thd_arg;
@@ -3505,7 +3505,7 @@ bool Item_in_subselect::fix_fields(THD *thd_arg, Item **ref)
  if (test_strategy(SUBS_SEMI_JOIN))
  DBUG_RETURN( !( (*ref)= new (thd->mem_root) Item_int(thd, 1)) );
 
- thd->where= "IN/ALL/ANY subquery";
+ thd->where= THD_WHERE::IN_ALL_ANY_SUBQUERY;
  /*
  Check if the outer and inner IN operands match in those cases when we
  will not perform IN=>EXISTS transformation. Currently this is when we
@@ -4016,7 +4016,7 @@ int join_read_next_same_or_null(READ_RECORD *info);
 
 int subselect_single_select_engine::exec()
 {
- char const *save_where= thd->where;
+ THD_WHERE save_where= thd->where;
  SELECT_LEX *save_select= thd->lex->current_select;
  thd->lex->current_select= select_lex;
  DBUG_ENTER("subselect_single_select_engine::exec");
@@ -4137,7 +4137,7 @@ int subselect_single_select_engine::exec()
 
 int subselect_union_engine::exec()
 {
- char const *save_where= thd->where;
+ THD_WHERE save_where= thd->where;
  int res= unit->exec();
  thd->where= save_where;
  return res;

sql/json_table.cc

@@ -1146,7 +1146,7 @@ bool push_table_function_arg_context(LEX *lex, MEM_ROOT *alloc)
 bool Table_function_json_table::setup(THD *thd, TABLE_LIST *sql_table,
  SELECT_LEX *s_lex)
 {
- thd->where= "JSON_TABLE argument";
+ thd->where= THD_WHERE::JSON_TABLE_ARGUMENT;
 
  if (!m_context_setup_done)
  {

sql/opt_subselect.cc

@@ -638,8 +638,8 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
  {
  SELECT_LEX *current= thd->lex->current_select;
  thd->lex->current_select= current->return_after_parsing();
- char const *save_where= thd->where;
- thd->where= "IN/ALL/ANY subquery";
+ THD_WHERE save_where= thd->where;
+ thd->where= THD_WHERE::IN_ALL_ANY_SUBQUERY;
 
  Item **left= in_subs->left_exp_ptr();
  bool failure= (*left)->fix_fields_if_needed(thd, left);

sql/partition_info.cc

@@ -1824,7 +1824,7 @@ bool partition_info::add_column_list_value(THD *thd, Item *item)
  part_column_list_val *col_val;
  Name_resolution_context *context= &thd->lex->current_select->context;
  TABLE_LIST *save_list= context->table_list;
- const char *save_where= thd->where;
+ THD_WHERE save_where= thd->where;
  DBUG_ENTER("partition_info::add_column_list_value");
 
  if (part_type == LIST_PARTITION &&
@@ -1838,9 +1838,9 @@ bool partition_info::add_column_list_value(THD *thd, Item *item)
 
  context->table_list= 0;
  if (column_list)
- thd->where= "field list";
+ thd->where= THD_WHERE::FIELD_LIST;
  else
- thd->where= "partition function";
+ thd->where= THD_WHERE::PARTITION_FUNCTION;
 
  if (item->walk(&Item::check_partition_func_processor, 0, NULL))
  {

sql/sql_base.cc

@@ -5955,7 +5955,7 @@ find_field_in_natural_join(THD *thd, TABLE_LIST *table_ref, const char *name, si
  {
  if (nj_col)
  {
- my_error(ER_NON_UNIQ_ERROR, MYF(0), name, thd->where);
+ my_error(ER_NON_UNIQ_ERROR, MYF(0), name, thd_where(thd));
  DBUG_RETURN(NULL);
  }
  nj_col= curr_nj_col;
@@ -6602,7 +6602,7 @@ find_field_in_tables(THD *thd, Item_ident *item,
  item->cached_field_index= NO_CACHED_FIELD_INDEX;
  }
 
- DBUG_ASSERT(thd->where);
+ DBUG_ASSERT(thd->where != THD_WHERE::NOWHERE);
  /*
  If we found a fully qualified field we return it directly as it can't
  have duplicates.
@@ -6615,7 +6615,7 @@ find_field_in_tables(THD *thd, Item_ident *item,
  if (report_error == REPORT_ALL_ERRORS ||
  report_error == IGNORE_EXCEPT_NON_UNIQUE)
  my_error(ER_NON_UNIQ_ERROR, MYF(0),
- table_name ? item->full_name() : name, thd->where);
+ table_name ? item->full_name() : name, thd_where(thd));
  return (Field*) 0;
  }
  found= cur_field;
@@ -6643,13 +6643,13 @@ find_field_in_tables(THD *thd, Item_ident *item,
  strxnmov(buff,sizeof(buff)-1,db,".",table_name,NullS);
  table_name=buff;
  }
- my_error(ER_UNKNOWN_TABLE, MYF(0), table_name, thd->where);
+ my_error(ER_UNKNOWN_TABLE, MYF(0), table_name, thd_where(thd));
  }
  else
  {
  if (report_error == REPORT_ALL_ERRORS ||
  report_error == REPORT_EXCEPT_NON_UNIQUE)
- my_error(ER_BAD_FIELD_ERROR, MYF(0), item->full_name(), thd->where);
+ my_error(ER_BAD_FIELD_ERROR, MYF(0), item->full_name(), thd_where(thd));
  else
  found= not_found_field;
  }
@@ -6782,7 +6782,7 @@ find_item_in_list(Item *find, List<Item> &items, uint *counter,
  */
  if (report_error != IGNORE_ERRORS)
  my_error(ER_NON_UNIQ_ERROR, MYF(0),
- find->full_name(), current_thd->where);
+ find->full_name(), thd_where(current_thd));
  return (Item**) 0;
  }
  found_unaliased= li.ref();
@@ -6813,7 +6813,7 @@ find_item_in_list(Item *find, List<Item> &items, uint *counter,
  continue; // Same field twice
  if (report_error != IGNORE_ERRORS)
  my_error(ER_NON_UNIQ_ERROR, MYF(0),
- find->full_name(), current_thd->where);
+ find->full_name(), thd_where(current_thd));
  return (Item**) 0;
  }
  found= li.ref();
@@ -6868,7 +6868,7 @@ find_item_in_list(Item *find, List<Item> &items, uint *counter,
  {
  if (report_error != IGNORE_ERRORS)
  my_error(ER_NON_UNIQ_ERROR, MYF(0),
- find->full_name(), current_thd->where);
+ find->full_name(), thd_where(current_thd));
  return (Item **) 0;
  }
  if (found_unaliased)
@@ -6885,7 +6885,7 @@ find_item_in_list(Item *find, List<Item> &items, uint *counter,
  {
  if (report_error == REPORT_ALL_ERRORS)
  my_error(ER_BAD_FIELD_ERROR, MYF(0),
- find->full_name(), current_thd->where);
+ find->full_name(), thd_where(current_thd));
  return (Item **) 0;
  }
  else
@@ -7091,7 +7091,7 @@ mark_common_columns(THD *thd, TABLE_LIST *table_ref_1, TABLE_LIST *table_ref_2,
  DBUG_PRINT ("info", ("match c1.is_common=%d", nj_col_1->is_common));
  if (cur_nj_col_2->is_common || found)
  {
- my_error(ER_NON_UNIQ_ERROR, MYF(0), field_name_1->str, thd->where);
+ my_error(ER_NON_UNIQ_ERROR, MYF(0), field_name_1->str, thd_where(thd));
  goto err;
  }
  if ((!using_fields && !field_2_invisible) || is_using_column_1)
@@ -7305,7 +7305,7 @@ store_natural_using_join_columns(THD *thd, TABLE_LIST *natural_using_join,
  if (!(common_field= it++))
  {
  my_error(ER_BAD_FIELD_ERROR, MYF(0), using_field_name_ptr,
- current_thd->where);
+ thd_where(current_thd));
  goto err;
  }
  if (!my_strcasecmp(system_charset_info,
@@ -7559,7 +7559,7 @@ static bool setup_natural_join_row_types(THD *thd,
  Name_resolution_context *context)
 {
  DBUG_ENTER("setup_natural_join_row_types");
- thd->where= "from clause";
+ thd->where= THD_WHERE::FROM_CLAUSE;
  if (from_clause->elements == 0)
  DBUG_RETURN(false); /* We come here in the case of UNIONs. */
 
@@ -7730,7 +7730,7 @@ bool setup_fields(THD *thd, Ref_ptr_array ref_pointer_array,
  thd->lex->current_select->nest_level);
  if (allow_sum_func)
  thd->lex->allow_sum_func.set_bit(thd->lex->current_select->nest_level);
- thd->where= THD::DEFAULT_WHERE;
+ thd->where= THD_WHERE::DEFAULT_WHERE;
  save_is_item_list_lookup= thd->lex->current_select->is_item_list_lookup;
  thd->lex->current_select->is_item_list_lookup= 0;
 
@@ -8489,7 +8489,7 @@ bool setup_on_expr(THD *thd, TABLE_LIST *table, bool is_update)
  embedded= embedding;
  if (embedded->on_expr)
  {
- thd->where="on clause";
+ thd->where= THD_WHERE::ON_CLAUSE;
  embedded->on_expr->mark_as_condition_AND_part(embedded);
  if (embedded->on_expr->fix_fields_if_needed_for_bool(thd,
  &embedded->on_expr))
@@ -8590,7 +8590,7 @@ int setup_conds(THD *thd, TABLE_LIST *tables, List<TABLE_LIST> &leaves,
 
  if (*conds)
  {
- thd->where="where clause";
+ thd->where= THD_WHERE::WHERE_CLAUSE;
  DBUG_EXECUTE("where",
  print_where(*conds,
  "WHERE in setup_conds",