github.com/dolthub/go-mysql-server@v0.18.0/sql/analyzer/resolve_orderby.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 analyzer
    16  
    17  import (
    18  	errors "gopkg.in/src-d/go-errors.v1"
    19  
    20  	"github.com/dolthub/go-mysql-server/sql"
    21  )
    22  
    23  var (
    24  	// ErrOrderByColumnIndex is returned when in an order clause there is a
    25  	// column that is unknown.
    26  	ErrOrderByColumnIndex = errors.NewKind("unknown column %d in order by clause")
    27  )
    28  
    29  // findFirstProjectorNode returns the first sql.Projector node found, starting the search from the specified node.
    30  // If the specified node is a sql.Projector, it will be returned, otherwise its children will be searched for the first
    31  // Projector until one is found. If no Projector is found, nil is returned.
    32  func findFirstProjectorNode(node sql.Node) sql.Projector {
    33  	children := []sql.Node{node}
    34  
    35  	for {
    36  		if len(children) == 0 {
    37  			return nil
    38  		}
    39  
    40  		currentChild := children[0]
    41  		children = children[1:]
    42  
    43  		if projector, ok := currentChild.(sql.Projector); ok {
    44  			return projector
    45  		}
    46  
    47  		children = append(children, currentChild.Children()...)
    48  	}
    49  }