Item_cache Class Reference

Inheritance diagram for Item_cache:

List of all members.

Public Member Functions
	Item_cache (enum_field_types field_type_arg)
void	set_used_tables (table_map map)
virtual table_map	resolved_used_tables () const
virtual bool	allocate (uint i)
virtual bool	setup (Item *item)
enum Type	type () const
enum_field_types	field_type () const
table_map	used_tables () const
virtual void	keep_array ()
virtual void	print (String *str, enum_query_type query_type)
bool	eq_def (Field *field)
bool	eq (const Item *item, bool binary_cmp) const
bool	has_value ()
Field *	field ()
virtual void	store (Item *item)
virtual bool	cache_value ()=0
bool	basic_const_item () const
bool	walk (Item_processor processor, bool walk_subquery, uchar *argument)
virtual void	clear ()
bool	is_null ()
Item_result	result_type () const
Static Public Member Functions
static Item_cache *	get_cache (const Item *item)
static Item_cache *	get_cache (const Item *item, const Item_result type)
Protected Attributes
Item *	example
table_map	used_table_map
Field *	cached_field
enum enum_field_types	cached_field_type
bool	value_cached

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Member Function Documentation

bool Item_cache::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.

Field* Item_cache::field

(

)

[inline]

If this item caches a field value, return pointer to underlying field.

Returns:

Pointer to field, or NULL if this is not a cache for a field value.

Item_cache * Item_cache::get_cache	(	const Item *	item,
		const Item_result	type
	)		[static]

Get a cache item of given type.

Parameters:

item	value to be cached
type	required type of cache

Returns:

cache item

bool Item_cache::has_value

(

)

[inline]

Check if saved item has a non-NULL value. Will cache value of saved item if not already done.

Returns:

TRUE if cached value is non-NULL.

void Item_cache::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.

virtual table_map Item_cache::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.

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Member Data Documentation

Field* Item_cache::cached_field [protected]

Field that this object will get value from. This is used by index-based subquery engines to detect and remove the equality injected by IN->EXISTS transformation.

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The documentation for this class was generated from the following files:

• item.h
• item.cc