github.com/dolthub/go-mysql-server@v0.18.0/sql/expression/star.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 expression
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"github.com/dolthub/go-mysql-server/sql"
    21  )
    22  
    23  // Star represents the selection of all available fields.
    24  // This is just a placeholder node, it will not actually be evaluated
    25  // but converted to a series of GetFields when the query is analyzed.
    26  type Star struct {
    27  	Table string
    28  }
    29  
    30  var _ sql.Expression = (*Star)(nil)
    31  var _ sql.CollationCoercible = (*Star)(nil)
    32  
    33  // NewStar returns a new Star expression.
    34  func NewStar() *Star {
    35  	return new(Star)
    36  }
    37  
    38  // NewQualifiedStar returns a new star expression only for a specific table.
    39  func NewQualifiedStar(table string) *Star {
    40  	return &Star{table}
    41  }
    42  
    43  // Resolved implements the Expression interface.
    44  func (*Star) Resolved() bool {
    45  	return false
    46  }
    47  
    48  // Children implements the Expression interface.
    49  func (*Star) Children() []sql.Expression {
    50  	return nil
    51  }
    52  
    53  // IsNullable implements the Expression interface.
    54  func (*Star) IsNullable() bool {
    55  	return false
    56  }
    57  
    58  // Type implements the Expression interface.
    59  func (*Star) Type() sql.Type {
    60  	panic("star is just a placeholder node, but Type was called")
    61  }
    62  
    63  // CollationCoercibility implements the interface sql.CollationCoercible.
    64  func (*Star) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    65  	return sql.Collation_binary, 7
    66  }
    67  
    68  func (s *Star) String() string {
    69  	if s.Table != "" {
    70  		return fmt.Sprintf("%s.*", s.Table)
    71  	}
    72  	return "*"
    73  }
    74  
    75  // Eval implements the Expression interface.
    76  func (*Star) Eval(ctx *sql.Context, r sql.Row) (interface{}, error) {
    77  	panic("star is just a placeholder node, but Eval was called")
    78  }
    79  
    80  // WithChildren implements the Expression interface.
    81  func (s *Star) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    82  	if len(children) != 0 {
    83  		return nil, sql.ErrInvalidChildrenNumber.New(s, len(children), 0)
    84  	}
    85  	return s, nil
    86  }