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values.go
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values.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 function
import (
"fmt"
"github.com/Rock-liyi/p2pdb-store/sql"
"github.com/Rock-liyi/p2pdb-store/sql/expression"
)
// Values is used in an ON DUPLICATE KEY UPDATE statement to return the value stated in the to-be-inserted column.
// For example, given the following statement:
// INSERT INTO table (pk, v1, v2) VALUES (1, 3, 5), (2, 4, 6) ON DUPLICATE KEY UPDATE v2 = values(v1) * 10;
// the values inserted into v2 would be 30 and 40.
type Values struct {
expression.UnaryExpression
Value interface{}
}
var _ sql.FunctionExpression = (*Values)(nil)
// NewValues creates a new Values function.
func NewValues(col sql.Expression) sql.Expression {
return &Values{
UnaryExpression: expression.UnaryExpression{Child: col},
Value: nil,
}
}
// Eval implements sql.FunctionExpression.
func (v *Values) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
// If Value is never assigned to then it has the nil value. It will only be assigned to in the ON DUPLICATE KEY UPDATE
// statement, therefore when used in every other context it will return nil, which is the correct and intended behavior.
return v.Value, nil
}
// FunctionName implements sql.FunctionExpression.
func (v *Values) FunctionName() string {
return "values"
}
// Description implements sql.FunctionExpression.
func (v *Values) Description() string {
return "defines the values to be used during an INSERT."
}
// String implements sql.FunctionExpression.
func (v *Values) String() string {
return fmt.Sprintf("VALUES(%s)", v.Child.String())
}
// Type implements sql.FunctionExpression.
func (v *Values) Type() sql.Type {
return v.Child.Type()
}
// WithChildren implements sql.FunctionExpression.
func (v *Values) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(v, len(children), 1)
}
return NewValues(children[0]), nil
}