MySQL  8.0.19
Source Code Documentation
AlternativeIterator Class Referencefinal

An iterator that switches between another iterator (typically a RefIterator or similar) and a TableScanIterator. More...

#include <ref_row_iterators.h>

Inheritance diagram for AlternativeIterator:
RowIterator

Public Member Functions

 AlternativeIterator (THD *thd, TABLE *table, QEP_TAB *qep_tab, ha_rows *examined_rows, unique_ptr_destroy_only< RowIterator > source, TABLE_REF *ref)
 
bool Init () override
 Initialize or reinitialize the iterator. More...
 
int Read () override
 Read a single row. 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 UnlockRow () override
 
std::vector< Childchildren () const override
 List of zero or more iterators which are direct children of this one. More...
 
std::vector< std::string > DebugString () const override
 Returns a short string (used for EXPLAIN FORMAT=tree) with user-readable information for this iterator. More...
 
- Public Member Functions inherited from RowIterator
 RowIterator (THD *thd)
 
virtual ~RowIterator ()
 
virtual std::string TimingString () const
 
JOINjoin_for_explain () const
 
void set_join_for_explain (JOIN *join)
 
virtual void StartPSIBatchMode ()
 Start performance schema batch mode, if supported (otherwise ignored). More...
 
virtual void EndPSIBatchModeIfStarted ()
 Ends performance schema batch mode, if started. More...
 
void set_estimated_cost (double estimated_cost)
 
double estimated_cost () const
 
void set_expected_rows (double expected_rows)
 
double expected_rows () const
 
virtual RowIteratorreal_iterator ()
 If this iterator is wrapping a different iterator (e.g. More...
 
virtual const RowIteratorreal_iterator () const
 

Private Attributes

TABLE_REFm_ref
 
std::vector< bool * > m_applicable_cond_guards
 
RowIteratorm_iterator = nullptr
 
RowIteratorm_last_iterator_inited = nullptr
 
unique_ptr_destroy_only< RowIteratorm_source_iterator
 
unique_ptr_destroy_only< RowIteratorm_table_scan_iterator
 
TABLE *const m_table
 

Additional Inherited Members

- Protected Member Functions inherited from RowIterator
THDthd () const
 

Detailed Description

An iterator that switches between another iterator (typically a RefIterator or similar) and a TableScanIterator.

This is used when predicates have been pushed down into an IN subquery and then created ref accesses, but said predicates should not be checked for a NULL value (so we need to revert to table scans). See QEP_TAB::pick_table_access_method() for a more thorough explanation.

Member Function Documentation

◆ children()

std::vector<Child> AlternativeIterator::children ( ) const
inlineoverridevirtual

List of zero or more iterators which are direct children of this one.

By convention, if there are multiple ones (ie., we're doing a join), the outer iterator is listed first. So for a LEFT JOIN b, we'd list a before b.

Reimplemented from RowIterator.

◆ Read()

int AlternativeIterator::Read ( )
inlineoverridevirtual

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
0OK
-1End of records
1Error

Implements RowIterator.

◆ SetNullRowFlag()

void AlternativeIterator::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 AlternativeIterator::UnlockRow ( )
inlineoverridevirtual

Implements RowIterator.

Member Data Documentation

◆ m_applicable_cond_guards

std::vector<bool *> AlternativeIterator::m_applicable_cond_guards
private

◆ m_iterator

RowIterator* AlternativeIterator::m_iterator = nullptr
private

◆ m_last_iterator_inited

RowIterator* AlternativeIterator::m_last_iterator_inited = nullptr
private

◆ m_ref

TABLE_REF* AlternativeIterator::m_ref
private

◆ m_source_iterator

unique_ptr_destroy_only<RowIterator> AlternativeIterator::m_source_iterator
private

◆ m_table

TABLE* const AlternativeIterator::m_table
private

◆ m_table_scan_iterator

unique_ptr_destroy_only<RowIterator> AlternativeIterator::m_table_scan_iterator
private

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