MySQL  8.0.27
Source Code Documentation
TableValueConstructorIterator Class Referencefinal

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:
RowIterator

Public Member Functions

 TableValueConstructorIterator (THD *thd, ha_rows *examined_rows, const mem_root_deque< mem_root_deque< Item * > * > &row_value_list, mem_root_deque< Item * > *join_fields)
 
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
 
virtual std::string TimingString () const
 
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 RowIteratorreal_iterator ()
 If this iterator is wrapping a different iterator (e.g. More...
 
virtual const RowIteratorreal_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_deque< Item * > *const m_output_refs
 References to the row we currently want to output. More...
 

Additional Inherited Members

- Protected Member Functions inherited from RowIterator
THDthd () 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_deque< Item * > *  join_fields 
)

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 TABLE_REF) 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
0OK
-1End of records
1Error

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_deque<Item *>* const 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.

◆ 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: