github.com/dolthub/go-mysql-server@v0.18.0/sql/plan/limit.go (about)

     1  // Copyright 2020-2021 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package plan
    16  
    17  import (
    18  	"github.com/dolthub/go-mysql-server/sql"
    19  )
    20  
    21  // Limit is a node that only allows up to N rows to be retrieved.
    22  type Limit struct {
    23  	UnaryNode
    24  	Limit         sql.Expression
    25  	CalcFoundRows bool
    26  }
    27  
    28  var _ sql.Node = (*Limit)(nil)
    29  var _ sql.CollationCoercible = (*Limit)(nil)
    30  
    31  // NewLimit creates a new Limit node with the given size.
    32  func NewLimit(size sql.Expression, child sql.Node) *Limit {
    33  	return &Limit{
    34  		UnaryNode: UnaryNode{Child: child},
    35  		Limit:     size,
    36  	}
    37  }
    38  
    39  // Expressions implements sql.Expressioner
    40  func (l *Limit) Expressions() []sql.Expression {
    41  	return []sql.Expression{l.Limit}
    42  }
    43  
    44  // WithExpressions implements sql.Expressioner
    45  func (l Limit) WithExpressions(exprs ...sql.Expression) (sql.Node, error) {
    46  	if len(exprs) != 1 {
    47  		return nil, sql.ErrInvalidChildrenNumber.New(l, len(exprs), 1)
    48  	}
    49  	nl := &l
    50  	nl.Limit = exprs[0]
    51  	return nl, nil
    52  }
    53  
    54  // Resolved implements the Resolvable interface.
    55  func (l *Limit) Resolved() bool {
    56  	return l.UnaryNode.Child.Resolved() && l.Limit.Resolved()
    57  }
    58  
    59  func (l Limit) WithCalcFoundRows(v bool) *Limit {
    60  	l.CalcFoundRows = v
    61  	return &l
    62  }
    63  
    64  func (l Limit) IsReadOnly() bool {
    65  	return l.Child.IsReadOnly()
    66  }
    67  
    68  // WithChildren implements the Node interface.
    69  func (l *Limit) WithChildren(children ...sql.Node) (sql.Node, error) {
    70  	if len(children) != 1 {
    71  		return nil, sql.ErrInvalidChildrenNumber.New(l, len(children), 1)
    72  	}
    73  
    74  	nl := *l
    75  	nl.Child = children[0]
    76  	return &nl, nil
    77  }
    78  
    79  // CheckPrivileges implements the interface sql.Node.
    80  func (l *Limit) CheckPrivileges(ctx *sql.Context, opChecker sql.PrivilegedOperationChecker) bool {
    81  	return l.Child.CheckPrivileges(ctx, opChecker)
    82  }
    83  
    84  // CollationCoercibility implements the interface sql.CollationCoercible.
    85  func (l *Limit) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    86  	return sql.GetCoercibility(ctx, l.Child)
    87  }
    88  
    89  func (l Limit) String() string {
    90  	pr := sql.NewTreePrinter()
    91  	_ = pr.WriteNode("Limit(%s)", l.Limit)
    92  	_ = pr.WriteChildren(l.Child.String())
    93  	return pr.String()
    94  }
    95  
    96  func (l Limit) DebugString() string {
    97  	pr := sql.NewTreePrinter()
    98  	_ = pr.WriteNode("Limit(%s)", l.Limit)
    99  	_ = pr.WriteChildren(sql.DebugString(l.Child))
   100  	return pr.String()
   101  }