// Select selects rows from a single table. Select is the workhorse of the SQL
// statements. In the slowest and most general case, select must perform full
// table scans across multiple tables and sort and join the resulting rows on
// arbitrary columns. Full table scans can be avoided when indexes can be used
// to satisfy the where-clause.
//
// Privileges: SELECT on table
// Notes: postgres requires SELECT. Also requires UPDATE on "FOR UPDATE".
// mysql requires SELECT.
func (p *planner) Select(n *parser.Select) (planNode, error) {
scan := &scanNode{txn: p.txn}
if err := scan.initFrom(p, n.From); err != nil {
return nil, err
}
if err := scan.initWhere(n.Where); err != nil {
return nil, err
}
if err := scan.initTargets(n.Exprs); err != nil {
return nil, err
}
group, err := p.groupBy(n, scan)
if err != nil {
return nil, err
}
if group != nil && n.OrderBy != nil {
// TODO(pmattis): orderBy currently uses deep knowledge of the
// scanNode. Need to lift that out or make orderBy compatible with
// groupNode as well.
return nil, fmt.Errorf("TODO(pmattis): unimplemented ORDER BY with GROUP BY/aggregation")
}
sort, err := p.orderBy(n, scan)
if err != nil {
return nil, err
}
// TODO(pmattis): Consider aggregation functions during index
// selection. Specifically, MIN(k) and MAX(k) where k is the first column in
// an index can be satisfied with a single read.
plan, err := p.selectIndex(scan, sort.Ordering())
if err != nil {
return nil, err
}
return sort.wrap(group.wrap(plan)), nil
}
func (p *planner) initSelect(s *selectNode, parsed *parser.Select) (planNode, *roachpb.Error) {
if pErr := s.initFrom(p, parsed); pErr != nil {
return nil, pErr
}
// TODO(radu): for now we assume from is always a scanNode
scan := s.from.(*scanNode)
// NB: both orderBy and groupBy are passed and can modify `scan` but orderBy must do so first.
sort, pErr := p.orderBy(parsed, scan)
if pErr != nil {
return nil, pErr
}
group, pErr := p.groupBy(parsed, scan)
if pErr != nil {
return nil, pErr
}
if scan.filter != nil && group != nil {
// Allow the group-by to add an implicit "IS NOT NULL" filter.
scan.filter = group.isNotNullFilter(scan.filter)
}
// Get the ordering for index selection (if any).
var ordering []int
var grouping bool
if group != nil {
ordering = group.desiredOrdering
grouping = true
} else if sort != nil {
ordering, _ = sort.Ordering()
}
plan, pErr := p.selectIndex(scan, ordering, grouping)
if pErr != nil {
return nil, pErr
}
// Update s.from with the new plan.
s.from = plan
// Wrap this node as necessary.
limit, pErr := p.limit(parsed, p.distinct(parsed, sort.wrap(group.wrap(s))))
if pErr != nil {
return nil, pErr
}
return limit, nil
}
// Select selects rows from a single table. Select is the workhorse of the SQL
// statements. In the slowest and most general case, select must perform full
// table scans across multiple tables and sort and join the resulting rows on
// arbitrary columns. Full table scans can be avoided when indexes can be used
// to satisfy the where-clause.
//
// Privileges: SELECT on table
// Notes: postgres requires SELECT. Also requires UPDATE on "FOR UPDATE".
// mysql requires SELECT.
func (p *planner) Select(n *parser.Select) (planNode, error) {
scan := &scanNode{planner: p, txn: p.txn}
if err := scan.initFrom(p, n.From); err != nil {
return nil, err
}
if err := scan.initWhere(n.Where); err != nil {
return nil, err
}
if err := scan.initTargets(n.Exprs); err != nil {
return nil, err
}
group, err := p.groupBy(n, scan)
if err != nil {
return nil, err
}
if group != nil && n.OrderBy != nil {
// TODO(pmattis): orderBy currently uses deep knowledge of the
// scanNode. Need to lift that out or make orderBy compatible with
// groupNode as well.
return nil, util.Errorf("TODO(pmattis): unimplemented ORDER BY with GROUP BY/aggregation")
}
sort, err := p.orderBy(n, scan)
if err != nil {
return nil, err
}
var ordering []int
if group != nil {
ordering = group.desiredOrdering
} else if sort != nil {
ordering, _ = sort.Ordering()
}
plan, err := p.selectIndex(scan, ordering)
if err != nil {
return nil, err
}
limit, err := p.limit(n, p.distinct(n, sort.wrap(group.wrap(plan))))
if err != nil {
return nil, err
}
return limit, nil
}
// Select selects rows from a single table. Select is the workhorse of the SQL
// statements. In the slowest and most general case, select must perform full
// table scans across multiple tables and sort and join the resulting rows on
// arbitrary columns. Full table scans can be avoided when indexes can be used
// to satisfy the where-clause.
//
// Privileges: SELECT on table
// Notes: postgres requires SELECT. Also requires UPDATE on "FOR UPDATE".
// mysql requires SELECT.
func (p *planner) Select(n *parser.Select) (planNode, error) {
scan := &scanNode{txn: p.txn}
if err := scan.initFrom(p, n.From); err != nil {
return nil, err
}
if err := scan.initWhere(n.Where); err != nil {
return nil, err
}
if err := scan.initTargets(n.Exprs); err != nil {
return nil, err
}
sort, err := p.orderBy(n, scan)
if err != nil {
return nil, err
}
plan, err := p.selectIndex(scan, sort.Ordering())
if err != nil {
return nil, err
}
return sort.wrap(plan), nil
}