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star.go
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star.go
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// Copyright 2020-2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package expression
import (
"fmt"
"github.com/Rock-liyi/p2pdb-store/sql"
)
// Star represents the selection of all available fields.
// This is just a placeholder node, it will not actually be evaluated
// but converted to a series of GetFields when the query is analyzed.
type Star struct {
Table string
}
// NewStar returns a new Star expression.
func NewStar() *Star {
return new(Star)
}
// NewQualifiedStar returns a new star expression only for a specific table.
func NewQualifiedStar(table string) *Star {
return &Star{table}
}
// Resolved implements the Expression interface.
func (*Star) Resolved() bool {
return false
}
// Children implements the Expression interface.
func (*Star) Children() []sql.Expression {
return nil
}
// IsNullable implements the Expression interface.
func (*Star) IsNullable() bool {
panic("star is just a placeholder node, but IsNullable was called")
}
// Type implements the Expression interface.
func (*Star) Type() sql.Type {
panic("star is just a placeholder node, but Type was called")
}
func (s *Star) String() string {
if s.Table != "" {
return fmt.Sprintf("%s.*", s.Table)
}
return "*"
}
// Eval implements the Expression interface.
func (*Star) Eval(ctx *sql.Context, r sql.Row) (interface{}, error) {
panic("star is just a placeholder node, but Eval was called")
}
// WithChildren implements the Expression interface.
func (s *Star) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 0 {
return nil, sql.ErrInvalidChildrenNumber.New(s, len(children), 0)
}
return s, nil
}