MDEV-9641 MDEV-9644 NULLIF assertions

* only copy args[0] to args[2] after fix_fields (when all item
  substitutions have already happened)

* change QT_ITEM_FUNC_NULLIF_TO_CASE (that allows to print NULLIF
  as CASE) to QT_ITEM_ORIGINAL_FUNC_NULLIF (that prohibits it).
  So that NULLIF-to-CASE is allowed by default and only disabled
  explicitly for SHOW VIEW|FUNCTION|PROCEDURE and mysql_make_view.
  By default it is allowed (in particular in error messages and
  debug output, that can happen anytime before or after optimizer).

mysql-test/r/null.result

@@ -1542,6 +1542,22 @@ nullif(count(col1),0)
 3
 drop view v1;
 drop table t1;
+select nullif((select 1), (select 2));
+nullif((select 1), (select 2))
+1
+create table t1 (f int);
+insert into t1 values (1),(2);
+select nullif( not f, 1 ) from t1;
+nullif( not f, 1 )
+0
+0
+drop table t1;
+set names utf8;
+create table t1 (f1 varchar(10));
+insert into t1 values ('2015-12-31');
+select power( timestamp( nullif( '2002-09-08', f1 ) ), 24 ) from t1;
+ERROR 22003: DOUBLE value is out of range in 'pow(cast((case when '2002-09-08' = '2015-12-31' then NULL else '2002-09-08' end) as datetime(6)),24)'
+drop table t1;
 #
 # End of 10.1 tests
 #

mysql-test/t/null.test

@@ -969,6 +969,25 @@ select nullif(count(col1),0) from t1;
 drop view v1;
 drop table t1;
 
+#
+# MDEV-9644 Assertion `args[0] == args[2] || thd->stmt_arena->is_stmt_execute()' failed in Item_func_nullif::fix_length_and_dec()
+#
+select nullif((select 1), (select 2));
+create table t1 (f int);
+insert into t1 values (1),(2);
+select nullif( not f, 1 ) from t1;
+drop table t1;
+
+#
+# MDEV-9641 Assertion `args[0] == args[2] || _current_thd()->lex->context_analysis_only' failed in Item_func_nullif::print(String*, enum_query_type)
+#
+set names utf8;
+create table t1 (f1 varchar(10));
+insert into t1 values ('2015-12-31');
+--error ER_DATA_OUT_OF_RANGE
+select power( timestamp( nullif( '2002-09-08', f1 ) ), 24 ) from t1;
+drop table t1;
+
 --echo #
 --echo # End of 10.1 tests
 --echo #

sql/item_cmpfunc.cc

@@ -2566,8 +2566,15 @@ void Item_func_nullif::update_used_tables()
 void
 Item_func_nullif::fix_length_and_dec()
 {
-  if (!args[2])					// Only false if EOM
-    return;
+  /*
+    If this is the first invocation of fix_length_and_dec(), create the
+    third argument as a copy of the first. This cannot be done before
+    fix_fields(), because fix_fields() might replace items,
+    for exampe NOT x --> x==0, or (SELECT 1) --> 1.
+    See also class Item_func_nullif declaration.
+  */
+  if (arg_count == 2)
+    args[arg_count++]= args[0];
 
   THD *thd= current_thd;
   /*
@@ -2706,7 +2713,7 @@ Item_func_nullif::fix_length_and_dec()
     m_cache= args[0]->cmp_type() == STRING_RESULT ?
              new (thd->mem_root) Item_cache_str_for_nullif(thd, args[0]) :
              Item_cache::get_cache(thd, args[0]);
-    m_cache->setup(current_thd, args[0]);
+    m_cache->setup(thd, args[0]);
     m_cache->store(args[0]);
     m_cache->set_used_tables(args[0]->used_tables());
     thd->change_item_tree(&args[0], m_cache);
@@ -2718,7 +2725,7 @@ Item_func_nullif::fix_length_and_dec()
   unsigned_flag= args[2]->unsigned_flag;
   fix_char_length(args[2]->max_char_length());
   maybe_null=1;
-  setup_args_and_comparator(current_thd, &cmp);
+  setup_args_and_comparator(thd, &cmp);
 }
 
 
@@ -2737,26 +2744,23 @@ void Item_func_nullif::print(String *str, enum_query_type query_type)
     Therefore, after equal field propagation args[0] and args[2] can point
     to different items.
   */
-  if (!(query_type & QT_ITEM_FUNC_NULLIF_TO_CASE) || args[0] == args[2])
+  if ((query_type & QT_ITEM_ORIGINAL_FUNC_NULLIF) || args[0] == args[2])
   {
     /*
-      If no QT_ITEM_FUNC_NULLIF_TO_CASE is requested,
+      If QT_ITEM_ORIGINAL_FUNC_NULLIF is requested,
       that means we want the original NULLIF() representation,
       e.g. when we are in:
         SHOW CREATE {VIEW|FUNCTION|PROCEDURE}
 
       The original representation is possible only if
       args[0] and args[2] still point to the same Item.
 
-      The caller must pass call print() with QT_ITEM_FUNC_NULLIF_TO_CASE
+      The caller must never pass call print() with QT_ITEM_ORIGINAL_FUNC_NULLIF
       if an expression has undergone some optimization
       (e.g. equal field propagation done in optimize_cond()) already and
       NULLIF() potentially has two different representations of "a":
       - one "a" for comparison
       - another "a" for the returned value!
-
-      Note, the EXPLAIN EXTENDED and EXPLAIN FORMAT=JSON routines
-      do pass QT_ITEM_FUNC_NULLIF_TO_CASE to print().
     */
     DBUG_ASSERT(args[0] == args[2] || current_thd->lex->context_analysis_only);
     str->append(func_name());
@@ -5789,7 +5793,7 @@ bool Item_func_not::fix_fields(THD *thd, Item **ref)
   args[0]->under_not(this);
   if (args[0]->type() == FIELD_ITEM)
   {
-    /* replace  "NOT <field>" with "<filed> == 0" */
+    /* replace  "NOT <field>" with "<field> == 0" */
     Query_arena backup, *arena;
     Item *new_item;
     bool rc= TRUE;

sql/item_cmpfunc.h

@@ -998,11 +998,18 @@ class Item_func_nullif :public Item_func_hybrid_field_type
   Item_cache *m_cache;
   int compare();
 public:
-  // Put "a" to args[0] for comparison and to args[2] for the returned value.
+  /*
+    Here we pass three arguments to the parent constructor, as NULLIF
+    is a three-argument function, it needs two copies of the first argument
+    (see above). But fix_fields() will be confused if we try to prepare the
+    same Item twice (if args[0]==args[2]), so we hide the third argument
+    (decrementing arg_count) and copy args[2]=args[0] again after fix_fields().
+    See also Item_func_nullif::fix_length_and_dec().
+  */
   Item_func_nullif(THD *thd, Item *a, Item *b):
     Item_func_hybrid_field_type(thd, a, b, a),
     m_cache(NULL)
-  {}
+  { arg_count--; }
   bool date_op(MYSQL_TIME *ltime, uint fuzzydate);
   double real_op();
   longlong int_op();

sql/mysqld.h

@@ -665,15 +665,16 @@ enum enum_query_type
   /// If NULLIF(a,b) should print itself as
   /// CASE WHEN a_for_comparison=b THEN NULL ELSE a_for_return_value END
   /// when "a" was replaced to two different items
-  /// (e.g. by equal fields propagation in optimize_cond()).
-  /// The default behaviour is to print as NULLIF(a_for_return, b)
-  /// which should be Ok for SHOW CREATE {VIEW|PROCEDURE|FUNCTION}
-  /// as they are not affected by WHERE optimization.
-  QT_ITEM_FUNC_NULLIF_TO_CASE= (1 <<6),
+  /// (e.g. by equal fields propagation in optimize_cond())
+  /// or always as NULLIF(a, b).
+  /// The default behaviour is to use CASE syntax when
+  /// a_for_return_value is not the same as a_for_comparison.
+  /// SHOW CREATE {VIEW|PROCEDURE|FUNCTION} and other cases where the
+  /// original representation is required, should set this flag.
+  QT_ITEM_ORIGINAL_FUNC_NULLIF= (1 <<6),
 
   /// This value means focus on readability, not on ability to parse back, etc.
   QT_EXPLAIN=           QT_TO_SYSTEM_CHARSET |
-                        QT_ITEM_FUNC_NULLIF_TO_CASE |
                         QT_ITEM_IDENT_SKIP_CURRENT_DATABASE |
                         QT_ITEM_CACHE_WRAPPER_SKIP_DETAILS |
                         QT_ITEM_SUBSELECT_ID_ONLY,
@@ -682,7 +683,7 @@ enum enum_query_type
   /// Be more detailed than QT_EXPLAIN.
   /// Perhaps we should eventually include QT_ITEM_IDENT_SKIP_CURRENT_DATABASE
   /// here, as it would give better readable results
-  QT_EXPLAIN_EXTENDED=  QT_TO_SYSTEM_CHARSET | QT_ITEM_FUNC_NULLIF_TO_CASE
+  QT_EXPLAIN_EXTENDED=  QT_TO_SYSTEM_CHARSET
 };
 
 

sql/sp_head.cc

@@ -3272,7 +3272,8 @@ sp_instr_set::print(String *str)
   }
   str->qs_append(m_offset);
   str->qs_append(' ');
-  m_value->print(str, QT_ORDINARY);
+  m_value->print(str, enum_query_type(QT_ORDINARY |
+                                      QT_ITEM_ORIGINAL_FUNC_NULLIF));
 }
 
 
@@ -3304,9 +3305,11 @@ void
 sp_instr_set_trigger_field::print(String *str)
 {
   str->append(STRING_WITH_LEN("set_trigger_field "));
-  trigger_field->print(str, QT_ORDINARY);
+  trigger_field->print(str, enum_query_type(QT_ORDINARY |
+                                            QT_ITEM_ORIGINAL_FUNC_NULLIF));
   str->append(STRING_WITH_LEN(":="));
-  value->print(str, QT_ORDINARY);
+  value->print(str, enum_query_type(QT_ORDINARY |
+                                    QT_ITEM_ORIGINAL_FUNC_NULLIF));
 }
 
 /*
@@ -3432,7 +3435,8 @@ sp_instr_jump_if_not::print(String *str)
   str->qs_append('(');
   str->qs_append(m_cont_dest);
   str->qs_append(STRING_WITH_LEN(") "));
-  m_expr->print(str, QT_ORDINARY);
+  m_expr->print(str, enum_query_type(QT_ORDINARY |
+                                     QT_ITEM_ORIGINAL_FUNC_NULLIF));
 }
 
 
@@ -3528,7 +3532,8 @@ sp_instr_freturn::print(String *str)
   str->qs_append(STRING_WITH_LEN("freturn "));
   str->qs_append((uint)m_type);
   str->qs_append(' ');
-  m_value->print(str, QT_ORDINARY);
+  m_value->print(str, enum_query_type(QT_ORDINARY |
+                                      QT_ITEM_ORIGINAL_FUNC_NULLIF));
 }
 
 /*
@@ -4000,7 +4005,8 @@ sp_instr_set_case_expr::print(String *str)
   str->qs_append(STRING_WITH_LEN(") "));
   str->qs_append(m_case_expr_id);
   str->qs_append(' ');
-  m_case_expr->print(str, QT_ORDINARY);
+  m_case_expr->print(str, enum_query_type(QT_ORDINARY |
+                                          QT_ITEM_ORIGINAL_FUNC_NULLIF));
 }
 
 uint

sql/sql_lex.cc

@@ -2689,7 +2689,7 @@ void st_select_lex::print_order(String *str,
   {
     if (order->counter_used)
     {
-      if (query_type != QT_VIEW_INTERNAL)
+      if (!(query_type & QT_VIEW_INTERNAL))
       {
         char buffer[20];
         size_t length= my_snprintf(buffer, 20, "%d", order->counter);

sql/sql_show.cc

@@ -2352,7 +2352,8 @@ static int show_create_view(THD *thd, TABLE_LIST *table, String *buff)
     We can't just use table->query, because our SQL_MODE may trigger
     a different syntax, like when ANSI_QUOTES is defined.
   */
-  table->view->unit.print(buff, QT_ORDINARY);
+  table->view->unit.print(buff, enum_query_type(QT_ORDINARY |
+                                                QT_ITEM_ORIGINAL_FUNC_NULLIF));
 
   if (table->with_check != VIEW_CHECK_NONE)
   {

sql/sql_view.cc

@@ -901,9 +901,11 @@ static int mysql_register_view(THD *thd, TABLE_LIST *view,
     ulong sql_mode= thd->variables.sql_mode & MODE_ANSI_QUOTES;
     thd->variables.sql_mode&= ~MODE_ANSI_QUOTES;
 
-    lex->unit.print(&view_query, QT_VIEW_INTERNAL);
-    lex->unit.print(&is_query,
-                    enum_query_type(QT_TO_SYSTEM_CHARSET | QT_WITHOUT_INTRODUCERS));
+    lex->unit.print(&view_query, enum_query_type(QT_VIEW_INTERNAL |
+                                                 QT_ITEM_ORIGINAL_FUNC_NULLIF));
+    lex->unit.print(&is_query, enum_query_type(QT_TO_SYSTEM_CHARSET |
+                                               QT_WITHOUT_INTRODUCERS |
+                                               QT_ITEM_ORIGINAL_FUNC_NULLIF));
 
     thd->variables.sql_mode|= sql_mode;
   }