Explain Class Reference

Inheritance diagram for Explain:

List of all members.

Classes
class	Lazy_condition
Public Member Functions
bool	send ()
Protected Member Functions
	Explain (Explain_context_enum context_type_arg, THD *thd_arg, JOIN *join_arg=NULL)
virtual bool	shallow_explain ()
bool	explain_subqueries (select_result *result)
bool	mark_subqueries (Item *item, qep_row *destination, Explain_context_enum type)
bool	mark_order_subqueries (const JOIN::ORDER_with_src &order)
bool	prepare_columns ()
bool	describe (uint8 mask) const
SELECT_LEX *	select_lex () const
bool	prepare (select_result *result)
bool	push_extra (Extra_tag tag)
bool	push_extra (Extra_tag tag, const String &arg)
bool	push_extra (Extra_tag tag, const char *arg)
virtual bool	explain_id ()
virtual bool	explain_select_type ()
virtual bool	explain_table_name ()
virtual bool	explain_partitions ()
virtual bool	explain_join_type ()
virtual bool	explain_possible_keys ()
virtual bool	explain_key_and_len ()
virtual bool	explain_ref ()
virtual bool	explain_rows_and_filtered ()
virtual bool	explain_extra ()
virtual bool	explain_modify_flags ()
Protected Attributes
THD *const	thd
	cached THD pointer
const CHARSET_INFO *const	cs
	cached pointer to system_charset_info
JOIN *const	join
	top-level JOIN (if any) provided by caller
select_result *const	external_result
	stream (if any) provided by caller
Explain_format *const	fmt
	shortcut for thd->lex->explain_format
Explain_context_enum	context_type
	associated value for struct. explain
JOIN::ORDER_with_src	order_list
JOIN::ORDER_with_src	group_list

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Detailed Description

A base for all Explain_* classes

Explain_* classes collect and output EXPLAIN data.

This class hierarchy is a successor of the old select_describe() function of 5.5.

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Member Function Documentation

virtual bool Explain::explain_key_and_len

(

)

[inline, protected, virtual]

fill col_key and and col_key_len fields together

Reimplemented in Explain_join.

virtual bool Explain::explain_rows_and_filtered

(

)

[inline, protected, virtual]

fill col_rows and col_filtered fields together

Reimplemented in Explain_join, and Explain_no_table.

bool Explain::explain_subqueries

(

select_result *

result

)

[protected]

Explain the rest of things after the shallow_explain() call

Traverses SQL clauses of this query specification to identify children subqueries, marks each of them with the clause they belong to. Then goes though all children subqueries and produces their EXPLAIN output, attached to the proper clause's context.

Parameters:

result

result stream

Return values:

false	Ok
true	Error (OOM)

bool Explain::mark_subqueries	(	Item *	item,
		qep_row *	destination,
		Explain_context_enum	type
	)		[protected]

Qualify subqueries with WHERE/HAVING/ORDER BY/GROUP BY clause type marker

Parameters:

item	Item tree to find subqueries
destination	For WHERE clauses
type	Clause type

Note:

WHERE clause belongs to TABLE or JOIN_TAB. The destination parameter provides a pointer to QEP data for such a table to associate a future subquery EXPLAIN output with table QEP provided.

Return values:

false	OK
true	Error

bool Explain::prepare

(

select_result *

result

)

[inline, protected]

Prepare the self-allocated result object

For queries with top-level JOIN the caller provides pre-allocated select_send object. Then that JOIN object prepares the select_send object calling result->prepare() in JOIN::prepare(), result->initalize_tables() in JOIN::optimize() and result->prepare2() in JOIN::exec(). However without the presence of the top-level JOIN we have to prepare/initialize select_send object manually.

bool Explain::prepare_columns

(

)

[protected]

Pre-calculate table property values for further EXPLAIN output

bool Explain::push_extra

(

Extra_tag

tag

)

[inline, protected]

Push a part of the "extra" column into formatter

Traditional formatter outputs traditional_extra_tags[tag] as is. Hierarchical formatter outputs a property with the json_extra_tags[tag] name and a boolean value of true.

Parameters:

tag	type of the "extra" part

Return values:

false	Ok
true	Error (OOM)

bool Explain::push_extra	(	Extra_tag	tag,
		const String &	arg
	)		[inline, protected]

Push a part of the "extra" column into formatter

Parameters:

tag	type of the "extra" part
arg	for traditional formatter: rest of the part text, for hierarchical format: string value of the property

Return values:

false	Ok
true	Error (OOM)

bool Explain::push_extra	(	Extra_tag	tag,
		const char *	arg
	)		[inline, protected]

Push a part of the "extra" column into formatter

Parameters:

tag	type of the "extra" part
arg	for traditional formatter: rest of the part text, for hierarchical format: string value of the property

NOTE: arg must be a long-living string constant.

Return values:

false	Ok
true	Error (OOM)

bool Explain::send

(

)

Explain class main function

This function: a) allocates a select_send object (if no one pre-allocated available), b) calculates and sends whole EXPLAIN data.

Returns:

false if success, true if error

bool Explain::shallow_explain

(

)

[protected, virtual]

Explain everything but subqueries

Reimplemented in Explain_join, and Explain_no_table.

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

• opt_explain.cc