Inheritance diagram for Item_ref:

Public Types
enum	Ref_Type { REF, DIRECT_REF, VIEW_REF, OUTER_REF, AGGREGATE_REF }
Public Member Functions
	Item_ref (Name_resolution_context context_arg, const char db_arg, const char table_name_arg, const char field_name_arg)
	Item_ref (Name_resolution_context context_arg, Item item, const char table_name_arg, const char *field_name_arg, bool alias_name_used_arg=FALSE)
	Item_ref (THD thd, Item_ref item)
enum Type	type () const
bool	eq (const Item *item, bool binary_cmp) const
double	val_real ()
longlong	val_int ()
longlong	val_time_temporal ()
longlong	val_date_temporal ()
my_decimal *	val_decimal (my_decimal *)
bool	val_bool ()
String *	val_str (String *tmp)
bool	is_null ()
bool	get_date (MYSQL_TIME *ltime, uint fuzzydate)
double	val_result ()
longlong	val_int_result ()
String *	str_result (String *tmp)
my_decimal *	val_decimal_result (my_decimal *)
bool	val_bool_result ()
bool	is_null_result ()
bool	send (Protocol prot, String tmp)
void	make_field (Send_field *field)
bool	fix_fields (THD , Item *)
void	fix_after_pullout (st_select_lex parent_select, st_select_lex removed_select)
type_conversion_status	save_in_field (Field *field, bool no_conversions)
void	save_org_in_field (Field *field)
enum Item_result	result_type () const
enum_field_types	field_type () const
Field *	get_tmp_table_field ()
Item *	get_tmp_table_item (THD *thd)
bool	const_item () const
table_map	used_tables () const
void	update_used_tables ()
virtual table_map	resolved_used_tables () const
table_map	not_null_tables () const
void	set_result_field (Field *field)
bool	is_result_field ()
void	save_in_result_field (bool no_conversions)
Item *	real_item ()
bool	walk (Item_processor processor, bool walk_subquery, uchar *arg)
virtual Item *	transform (Item_transformer, uchar *arg)
virtual Item *	compile (Item_analyzer analyzer, uchar *arg_p, Item_transformer transformer, uchar arg_t)
virtual bool	explain_subquery_checker (uchar **arg)
virtual void	print (String *str, enum_query_type query_type)
void	cleanup ()
Item_field *	field_for_view_update ()
virtual Ref_Type	ref_type ()
uint	cols ()
Item *	element_index (uint i)
Item **	addr (uint i)
bool	check_cols (uint c)
bool	null_inside ()
void	bring_value ()
bool	get_time (MYSQL_TIME *ltime)
virtual bool	basic_const_item () const
bool	is_outer_field () const
virtual bool	has_subquery () const
virtual bool	has_stored_program () const
virtual bool	created_by_in2exists () const
	Whether this Item was created by the IN->EXISTS subquery transformation.
Public Attributes
Field *	result_field
Item **	ref
Protected Member Functions
void	set_properties ()

Member Function Documentation

Item * Item_ref::compile	(	Item_analyzer	analyzer,
		uchar **	arg_p,
		Item_transformer	transformer,
		uchar *	arg_t
	)		`[virtual]`

Compile an Item_ref object with a processor and a transformer callback function.

First the function applies the analyzer to the Item_ref object. Second it applies the compile function to the object the Item_ref object is referencing. If this replaces the item with a new one, this object is returned as the result of the compile. Otherwise we apply the transformer to the Item_ref object itself.

Parameters:

	analyzer	the analyzer callback function to be applied to the nodes of the tree of the object
[in,out]	arg_p	parameter to be passed to the processor
	transformer	the transformer callback function to be applied to the nodes of the tree of the object
	arg_t	parameter to be passed to the transformer

Returns:: Item returned as the result of transformation of the Item_ref object, or NULL if error.

Reimplemented from Item.

bool Item_ref::eq	(	const Item *	item,
		bool	binary_cmp
	)		const `[inline, virtual]`

This function is called when:

Comparing items in the WHERE clause (when doing where optimization)
When trying to find an ORDER BY/GROUP BY item in the SELECT part
When matching fields in multiple equality objects (Item_equal)

Reimplemented from Item.

Reimplemented in Item_direct_view_ref.

void Item_ref::fix_after_pullout	(	st_select_lex *	parent_select,
		st_select_lex *	removed_select
	)		`[virtual]`

Fix after tables have been moved from one select_lex level to the parent level, e.g by semijoin conversion. Basically re-calculate all attributes dependent on the tables.

Parameters:

parent_select	select_lex that tables are moved to.
removed_select	select_lex that tables are moved away from, child of parent_select.

Reimplemented from Item_ident.

Reimplemented in Item_outer_ref.

bool Item_ref::fix_fields	(	THD *	thd,
		Item **	reference
	)		`[virtual]`

Resolve the name of a reference to a column reference.

The method resolves the column reference represented by 'this' as a column present in one of: GROUP BY clause, SELECT clause, outer queries. It is used typically for columns in the HAVING clause which are not under aggregate functions.

POSTCONDITION
Item_ref::ref is 0 or points to a valid item.

Note:: The name resolution algorithm used is (where [T_j] is an optional table name that qualifies the column name):

        resolve_extended([T_j].col_ref_i)
        {
          Search for a column or derived column named col_ref_i [in table T_j]
          in the SELECT and GROUP clauses of Q.

          if such a column is NOT found AND    // Lookup in outer queries.
             there are outer queries
          {
            for each outer query Q_k beginning from the inner-most one
           {
              Search for a column or derived column named col_ref_i
              [in table T_j] in the SELECT and GROUP clauses of Q_k.

              if such a column is not found AND
                 - Q_k is not a group query AND
                 - Q_k is not inside an aggregate function
                 OR
                 - Q_(k-1) is not in a HAVING or SELECT clause of Q_k
              {
                search for a column or derived column named col_ref_i
                [in table T_j] in the FROM clause of Q_k;
              }
            }
          }
        }

This procedure treats GROUP BY and SELECT clauses as one namespace for column references in HAVING. Notice that compared to Item_field::fix_fields, here we first search the SELECT and GROUP BY clauses, and then we search the FROM clause.

Parameters:

[in]	thd	current thread
[in,out]	reference	view column if this item was resolved to a view column

Todo:: Here we could first find the field anyway, and then test this condition, so that we can give a better error message - ER_WRONG_FIELD_WITH_GROUP, instead of the less informative ER_BAD_FIELD_ERROR which we produce now.

Return values:

TRUE	if error
FALSE	on success

Reimplemented from Item.

Reimplemented in Item_outer_ref, and Item_direct_view_ref.

virtual bool Item_ref::has_stored_program ( ) const [inline, virtual]

Checks if the item tree that ref points to contains a stored program.

Reimplemented from Item.

virtual bool Item_ref::has_subquery ( ) const [inline, virtual]

Checks if the item tree that ref points to contains a subquery.

Reimplemented from Item.

void Item_ref::print	(	String *	str,
		enum_query_type	query_type
	)		`[virtual]`

This method is used for to:

to generate a view definition query (SELECT-statement);
to generate a SQL-query for EXPLAIN EXTENDED;
to generate a SQL-query to be shown in INFORMATION_SCHEMA;
debug.

For more information about view definition query, INFORMATION_SCHEMA query and why they should be generated from the Item-tree,

See also:: mysql_register_view().

Reimplemented from Item_ident.

Reimplemented in Item_ref_null_helper, and Item_aggregate_ref.

virtual table_map Item_ref::resolved_used_tables ( ) const [inline, virtual]

Return used table information for the level this item is resolved on.

For fields, this returns the table the item is resolved from.
For all other items, this behaves like used_tables().

Note:: : Use this function with caution. External calls to this function should only be made for class objects derived from Item_ident. Item::resolved_used_tables is for internal use only, in order to process fields underlying a view column reference.

Reimplemented from Item.

type_conversion_status Item_ref::save_in_field	(	Field *	field,
		bool	no_conversions
	)		`[virtual]`

Save a temporal value in packed longlong format into a Field. Used in optimizer.

Parameters:

OUT	field The field to set the value to.

Return values:

0	On success.
>0	In error.

Reimplemented from Item.

bool Item_ref::send	(	Protocol *	protocol,
		String *	buffer
	)		`[virtual]`

This is only called from items that is not of type item_field.

Reimplemented from Item.

Item * Item_ref::transform	(	Item_transformer	transformer,
		uchar *	arg
	)		`[virtual]`

Transform an Item_ref object with a transformer callback function.

The function first applies the transform function to the item referenced by this Item_ref object. If this replaces the item with a new one, this item object is returned as the result of the transform. Otherwise the transform function is applied to the Item_ref object itself.

Parameters: