// EvalSubquery evaluates a subquery.
func EvalSubquery(ctx context.Context, v *ast.SubqueryExpr) error {
if v.SubqueryExec != nil {
rowCount := 2
if v.MultiRows {
rowCount = -1
} else if v.Exists {
rowCount = 1
}
rows, err := v.SubqueryExec.EvalRows(ctx, rowCount)
if err != nil {
return errors.Trace(err)
}
if v.MultiRows || v.Exists {
v.GetDatum().SetRow(rows)
v.Evaluated = true
return nil
}
switch len(rows) {
case 0:
v.SetNull()
case 1:
v.SetDatum(rows[0])
default:
return errors.New("Subquery returns more than 1 row")
}
}
v.Evaluated = true
return nil
}
// Evaluate SubqueryExpr.
// Get the value from v.SubQuery and set it to v.
func (e *Evaluator) subqueryExpr(v *ast.SubqueryExpr) bool {
if v.SubqueryExec != nil {
v.SetValue(v.SubqueryExec.GetValue())
}
v.Evaluated = true
return true
}