func hasSubquery(node sqlparser.SQLNode) bool {
has := false
_ = sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
if _, ok := node.(*sqlparser.Subquery); ok {
has = true
return false, errors.New("dummy")
}
return true, nil
}, node)
return has
}
// findRoute identifies the right-most route for expr. In situations where
// the expression addresses multiple routes, the expectation is that the
// executor will use the results of the previous routes to feed the necessary
// values for the external references.
// If the expression contains a subquery, the right-most route identification
// also follows the same rules of a normal expression. This is achieved by
// looking at the Externs field of its symbol table that contains the list of
// external references.
// Once the target route is identified, we have to verify that the subquery's
// route can be merged with it. If it cannot, we fail the query. This is because
// we don't have the ability to wire up subqueries through expression evaluation
// primitives. Consequently, if the plan for a subquery comes out as a Join,
// we can immediately error out.
// Since findRoute can itself be called from within a subquery, it has to assume
// that some of the external references may actually be pointing to an outer
// query. The isLocal response from the symtab is used to make sure that we
// only analyze symbols that point to the current symtab.
// If an expression has no references to the current query, then the left-most
// route is chosen as the default.
func findRoute(expr sqlparser.Expr, bldr builder) (rb *route, err error) {
highestRoute := bldr.Leftmost()
var subroutes []*route
err = sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
switch node := node.(type) {
case *sqlparser.ColName:
newRoute, isLocal, err := bldr.Symtab().Find(node, true)
if err != nil {
return false, err
}
if isLocal && newRoute.Order() > highestRoute.Order() {
highestRoute = newRoute
}
case *sqlparser.Subquery:
sel, ok := node.Select.(*sqlparser.Select)
if !ok {
return false, errors.New("unsupported: union operator in subqueries")
}
subplan, err := processSelect(sel, bldr.Symtab().VSchema, bldr)
if err != nil {
return false, err
}
subroute, ok := subplan.(*route)
if !ok {
return false, errors.New("unsupported: complex join in subqueries")
}
for _, extern := range subroute.Symtab().Externs {
// No error expected. These are resolved externs.
newRoute, isLocal, _ := bldr.Symtab().Find(extern, false)
if isLocal && newRoute.Order() > highestRoute.Order() {
highestRoute = newRoute
}
}
subroutes = append(subroutes, subroute)
return false, nil
}
return true, nil
}, expr)
if err != nil {
return nil, err
}
for _, subroute := range subroutes {
err = subqueryCanMerge(highestRoute, subroute)
if err != nil {
return nil, err
}
// This should be moved out if we become capable of processing
// subqueries without push-down.
subroute.Redirect = highestRoute
}
return highestRoute, nil
}
// getBindvars returns a map of the bind vars referenced in the statement.
func getBindvars(node sqlparser.SQLNode) map[string]struct{} {
bindvars := make(map[string]struct{})
_ = sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
switch node := node.(type) {
case sqlparser.ValArg:
bindvars[string(node[1:])] = struct{}{}
case sqlparser.ListArg:
bindvars[string(node[2:])] = struct{}{}
}
return true, nil
}, node)
return bindvars
}
// pushGroupBy processes the group by clause. It resolves all symbols,
// and ensures that there are no subqueries. It also verifies that the
// references don't addres an outer query. We only support group by
// for unsharded or single shard routes.
func pushGroupBy(groupBy sqlparser.GroupBy, bldr builder) error {
if groupBy == nil {
return nil
}
rb, ok := bldr.(*route)
if !ok {
return errors.New("unsupported: complex join and group by")
}
err := sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
switch node := node.(type) {
case *sqlparser.ColName:
_, isLocal, err := bldr.Symtab().Find(node, true)
if err != nil {
return false, err
}
if !isLocal {
return false, errors.New("unsupported: subquery references outer query in group by")
}
case *sqlparser.Subquery:
// TODO(sougou): better error.
return false, errors.New("unsupported: subqueries in group by expression")
}
return true, nil
}, groupBy)
if err != nil {
return err
}
if rb.IsSingle() {
rb.SetGroupBy(groupBy)
return nil
}
// It's a scatter route. We can allow group by if it references a
// column with a unique vindex.
for _, expr := range groupBy {
vindex := bldr.Symtab().Vindex(expr, rb, true)
if vindex != nil && vindexes.IsUnique(vindex) {
rb.SetGroupBy(groupBy)
return nil
}
}
return errors.New("unsupported: scatter and group by")
}
// checkAggregates returns an error if the select statement
// has aggregates that cannot be pushed down due to a complex
// plan.
func checkAggregates(sel *sqlparser.Select, bldr builder) error {
hasAggregates := false
if sel.Distinct != "" {
hasAggregates = true
} else {
_ = sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
switch node := node.(type) {
case *sqlparser.FuncExpr:
if node.IsAggregate() {
hasAggregates = true
return false, errors.New("dummy")
}
}
return true, nil
}, sel.SelectExprs)
}
if !hasAggregates {
return nil
}
// Check if we can allow aggregates.
rb, ok := bldr.(*route)
if !ok {
return errors.New("unsupported: complex join with aggregates")
}
if rb.IsSingle() {
return nil
}
// It's a scatter rb. We can allow aggregates if there is a unique
// vindex in the select list.
for _, selectExpr := range sel.SelectExprs {
switch selectExpr := selectExpr.(type) {
case *sqlparser.NonStarExpr:
vindex := bldr.Symtab().Vindex(selectExpr.Expr, rb, true)
if vindex != nil && vindexes.IsUnique(vindex) {
return nil
}
}
}
return errors.New("unsupported: scatter with aggregates")
}
// Wireup performs the wire-up tasks.
func (rb *route) Wireup(bldr builder, jt *jointab) error {
// Resolve values stored in the builder.
var err error
switch vals := rb.ERoute.Values.(type) {
case *sqlparser.ComparisonExpr:
// A comparison expression is stored only if it was an IN clause.
// We have to convert it to use a list argutment and resolve values.
rb.ERoute.Values, err = rb.procureValues(bldr, jt, vals.Right)
if err != nil {
return err
}
vals.Right = sqlparser.ListArg("::" + engine.ListVarName)
default:
rb.ERoute.Values, err = rb.procureValues(bldr, jt, vals)
if err != nil {
return err
}
}
// Fix up the AST.
_ = sqlparser.Walk(func(node sqlparser.SQLNode) (bool, error) {
switch node := node.(type) {
case *sqlparser.Select:
if len(node.SelectExprs) == 0 {
node.SelectExprs = sqlparser.SelectExprs([]sqlparser.SelectExpr{
&sqlparser.NonStarExpr{
Expr: sqlparser.NumVal([]byte{'1'}),
},
})
}
case *sqlparser.ComparisonExpr:
if node.Operator == sqlparser.EqualStr {
if exprIsValue(node.Left, rb) && !exprIsValue(node.Right, rb) {
node.Left, node.Right = node.Right, node.Left
}
}
}
return true, nil
}, &rb.Select)
// Generate query while simultaneously resolving values.
varFormatter := func(buf *sqlparser.TrackedBuffer, node sqlparser.SQLNode) {
switch node := node.(type) {
case *sqlparser.ColName:
if !rb.isLocal(node) {
joinVar := jt.Procure(bldr, node, rb.Order())
rb.ERoute.JoinVars[joinVar] = struct{}{}
buf.Myprintf("%a", ":"+joinVar)
return
}
case *sqlparser.TableName:
node.Name.Format(buf)
return
}
node.Format(buf)
}
buf := sqlparser.NewTrackedBuffer(varFormatter)
varFormatter(buf, &rb.Select)
rb.ERoute.Query = buf.ParsedQuery().Query
rb.ERoute.FieldQuery = rb.generateFieldQuery(&rb.Select, jt)
return nil
}