TableValueConstructorIterator Class Reference

TableValueConstructor is the iterator for the table value constructor case of a query_primary (i.e. More...

#include <basic_row_iterators.h>

Inheritance diagram for TableValueConstructorIterator:

Public Member Functions
	TableValueConstructorIterator (THD *thd, ha_rows *examined_rows, const mem_root_deque< mem_root_deque< Item * > * > &row_value_list, Mem_root_array< Item_values_column * > *output_refs)
bool	Init () override
	Initialize or reinitialize the iterator. More...
int	Read () override
	Read a single row. More...
void	SetNullRowFlag (bool) 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	UnlockRow () override
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 void	StartPSIBatchMode ()
	Start performance schema batch mode, if supported (otherwise ignored). More...
virtual void	EndPSIBatchModeIfStarted ()
	Ends performance schema batch mode, if started. More...
virtual RowIterator *	real_iterator ()
	If this iterator is wrapping a different iterator (e.g. More...
virtual const RowIterator *	real_iterator () const

Private Attributes
ha_rows *const	m_examined_rows {nullptr}
const mem_root_deque< mem_root_deque< Item * > * > &	m_row_value_list
	Contains the row values that are part of a VALUES clause. More...
mem_root_deque< mem_root_deque< Item * > * >::const_iterator	m_row_it
Mem_root_array< Item_values_column * > *	m_output_refs
	References to the row we currently want to output. More...

Additional Inherited Members
Protected Member Functions inherited from RowIterator
THD *	thd () const

Detailed Description

TableValueConstructor is the iterator for the table value constructor case of a query_primary (i.e.

queries of the form VALUES row_list; e.g. VALUES ROW(1, 10), ROW(2, 20)).

The iterator is passed the field list of its parent JOIN object, which may contain Item_values_column objects that are created during Query_block::prepare_values(). This is required so that Read() can replace the currently selected row by simply changing the references of Item_values_column objects to the next row.

The iterator must output multiple rows without being materialized, and does not scan any tables. The indirection of Item_values_column is required, as the executor outputs what is contained in join->fields (either directly, or indirectly through ConvertItemsToCopy), and is thus responsible for ensuring that join->fields contains the correct next row.

Constructor & Destructor Documentation

TableValueConstructorIterator()

TableValueConstructorIterator::TableValueConstructorIterator	(	THD *	thd,
		ha_rows *	examined_rows,
		const mem_root_deque< mem_root_deque< Item * > * > &	row_value_list,
		Mem_root_array< Item_values_column * > *	output_refs
	)

Member Function Documentation

Init()

bool TableValueConstructorIterator::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 TableValueConstructorIterator::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.

SetNullRowFlag()

void TableValueConstructorIterator::SetNullRowFlag ( bool  is_null_row )

inlineoverridevirtual

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).

This is used for outer joins, when an iterator hasn't produced any rows and we need to produce a NULL-complemented row. Init() or Read() won't necessarily reset this flag, so if you ever set is to true, make sure to also set it to false when needed.

Note that this can be called without Init() having been called first. For example, NestedLoopIterator can hit EOF immediately on the outer iterator, which means the inner iterator doesn't get an Init() call, but will still forward SetNullRowFlag to both inner and outer iterators.

TODO: We shouldn't need this. See the comments on AggregateIterator for a bit more discussion on abstracting out a row interface.

Implements RowIterator.

UnlockRow()

void TableValueConstructorIterator::UnlockRow ( )

inlineoverridevirtual

Implements RowIterator.

Member Data Documentation

m_examined_rows

ha_rows* const TableValueConstructorIterator::m_examined_rows {nullptr}

private

m_output_refs

Mem_root_array<Item_values_column *>* TableValueConstructorIterator::m_output_refs

private

References to the row we currently want to output.

When multiple rows must be output, this contains Item_values_column objects. In this case, each call to Read() will replace its current reference with the next row. It is nullptr if there is only one row.

m_row_it

mem_root_deque<mem_root_deque<Item*>*>::const_iterator TableValueConstructorIterator::m_row_it

private

m_row_value_list

const mem_root_deque<mem_root_deque<Item *> *>& TableValueConstructorIterator::m_row_value_list

private

Contains the row values that are part of a VALUES clause.

Read() will modify contained Item objects during execution by calls to is_null() and the required val function to extract its value.

---

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

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