TableScanIterator Class Reference

Scan a table from beginning to end. More...

#include <basic_row_iterators.h>

Inheritance diagram for TableScanIterator:

Public Member Functions
	TableScanIterator (THD *thd, TABLE *table, double expected_rows, ha_rows *examined_rows)
	~TableScanIterator () override
bool	Init () override
	Initialize or reinitialize the iterator. More...
int	Read () override
	Read a single row. More...
Public Member Functions inherited from TableRowIterator
	TableRowIterator (THD *thd, TABLE *table)
void	UnlockRow () override
	The default implementation of unlock-row method of RowIterator, used in all access methods except EQRefIterator. More...
void	SetNullRowFlag (bool is_null_row) override
	Mark the current row buffer as containing a NULL row or not, so that if you read from it and the flag is true, you'll get only NULLs no matter what is actually in the buffer (typically some old leftover row). More...
void	StartPSIBatchMode () override
	Start performance schema batch mode, if supported (otherwise ignored). More...
void	EndPSIBatchModeIfStarted () override
	Ends performance schema batch mode, if started. More...
Public Member Functions inherited from RowIterator
	RowIterator (THD *thd)
virtual	~RowIterator ()=default
	RowIterator (const RowIterator &)=delete
	RowIterator (RowIterator &&)=default
virtual const IteratorProfiler *	GetProfiler () const
	Get profiling data for this iterator (for 'EXPLAIN ANALYZE'). More...
virtual void	SetOverrideProfiler ([[maybe_unused]] const IteratorProfiler *profiler)
virtual RowIterator *	real_iterator ()
	If this iterator is wrapping a different iterator (e.g. More...
virtual const RowIterator *	real_iterator () const

Private Attributes
uchar *const	m_record
const double	m_expected_rows
ha_rows *const	m_examined_rows
ulonglong	m_remaining_dups {0}
	Used to keep track of how many more duplicates of the last read row that remains to be written to the next stage: used for EXCEPT and INTERSECT computation: we only ever materialize one row even if there are duplicates of it, but with a counter, cf TABLE::m_set_counter. More...
const ha_rows	m_limit_rows
	Used for EXCEPT and INTERSECT only: we cannot enforce limit during materialization as for UNION and single table, so we have to do it during the scan. More...
ha_rows	m_stored_rows {0}
	Used for EXCEPT and INTERSECT only: rows scanned so far, see also m_limit_rows. More...

Additional Inherited Members
Protected Member Functions inherited from TableRowIterator
int	HandleError (int error)
void	PrintError (int error)
TABLE *	table () const
Protected Member Functions inherited from RowIterator
THD *	thd () const

Detailed Description

Scan a table from beginning to end.

This is the most basic access method of a table using rnd_init, ha_rnd_next and rnd_end. No indexes are used.

Constructor & Destructor Documentation

TableScanIterator()

TableScanIterator::TableScanIterator	(	THD *	thd,
		TABLE *	table,
		double	expected_rows,
		ha_rows *	examined_rows
	)

Parameters

thd	session context
table	table to be scanned. Notice that table may be a temporary table that represents a set operation (UNION, INTERSECT or EXCEPT). For the latter two, the counter field must be interpreted by TableScanIterator::Read in order to give the correct result set, but this is invisible to the consumer.
expected_rows	is used for scaling the record buffer. If zero or less, no record buffer will be set up.
examined_rows	if not nullptr, is incremented for each successful Read().

~TableScanIterator()

TableScanIterator::~TableScanIterator ( )

override

Member Function Documentation

Init()

bool TableScanIterator::Init ( )

overridevirtual

Initialize or reinitialize the iterator.

You must always call Init() before trying a Read() (but Init() does not imply Read()).

You can call Init() multiple times; subsequent calls will rewind the iterator (or reposition it, depending on whether the iterator takes in e.g. a Index_lookup) and allow you to read the records anew.

Implements RowIterator.

Read()

int TableScanIterator::Read ( )

overridevirtual

Read a single row.

The row data is not actually returned from the function; it is put in the table's (or tables', in case of a join) record buffer, ie., table->records[0].

Return values

0	OK
-1	End of records
1	Error

Implements RowIterator.

Member Data Documentation

m_examined_rows

ha_rows* const TableScanIterator::m_examined_rows

private

m_expected_rows

const double TableScanIterator::m_expected_rows

private

m_limit_rows

const ha_rows TableScanIterator::m_limit_rows

private

Used for EXCEPT and INTERSECT only: we cannot enforce limit during materialization as for UNION and single table, so we have to do it during the scan.

m_record

uchar* const TableScanIterator::m_record

private

m_remaining_dups

ulonglong TableScanIterator::m_remaining_dups {0}

private

Used to keep track of how many more duplicates of the last read row that remains to be written to the next stage: used for EXCEPT and INTERSECT computation: we only ever materialize one row even if there are duplicates of it, but with a counter, cf TABLE::m_set_counter.

When we start scanning we must produce as many duplicates as ALL semantics mandate, so we initialize m_examined_rows based on TABLE::m_set_counter and decrement for each row we emit, so as to produce the correct number of duplicates for the next stage.

m_stored_rows

ha_rows TableScanIterator::m_stored_rows {0}

private

Used for EXCEPT and INTERSECT only: rows scanned so far, see also m_limit_rows.

---

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

• sql/iterators/basic_row_iterators.h
• sql/iterators/basic_row_iterators.cc