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

     1  // Copyright 2023 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  	"github.com/dolthub/go-mysql-server/sql/encodings"
    22  )
    23  
    24  // ConvertUsing represents a CONVERT(X USING T) operation that casts the expression X to the character set T.
    25  type ConvertUsing struct {
    26  	UnaryExpression
    27  	TargetCharSet sql.CharacterSetID
    28  }
    29  
    30  var _ sql.Expression = (*ConvertUsing)(nil)
    31  var _ sql.CollationCoercible = (*ConvertUsing)(nil)
    32  
    33  func NewConvertUsing(expr sql.Expression, targetCharSet sql.CharacterSetID) *ConvertUsing {
    34  	return &ConvertUsing{
    35  		UnaryExpression: UnaryExpression{Child: expr},
    36  		TargetCharSet:   targetCharSet,
    37  	}
    38  }
    39  
    40  // String implements the interface sql.Expression.
    41  func (c *ConvertUsing) String() string {
    42  	return fmt.Sprintf("CONVERT(%s USING %s)", c.Child.String(), c.TargetCharSet.Name())
    43  }
    44  
    45  // Type implements the interface sql.Expression.
    46  func (c *ConvertUsing) Type() sql.Type {
    47  	typ := c.Child.Type()
    48  	if collatedType, ok := typ.(sql.TypeWithCollation); ok {
    49  		newTyp, _ := collatedType.WithNewCollation(c.TargetCharSet.DefaultCollation())
    50  		return newTyp
    51  	}
    52  	return typ
    53  }
    54  
    55  // Eval implements the interface sql.Expression.
    56  func (c *ConvertUsing) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    57  	val, err := c.Child.Eval(ctx, row)
    58  	if err != nil {
    59  		return nil, err
    60  	}
    61  	if val == nil {
    62  		return nil, nil
    63  	}
    64  
    65  	var valBytes []byte
    66  	if v, ok := val.([]byte); ok {
    67  		valBytes = v
    68  	} else if v, ok := val.(string); ok {
    69  		valBytes = encodings.StringToBytes(v)
    70  	}
    71  	newString := c.TargetCharSet.Encoder().EncodeReplaceUnknown(valBytes)
    72  	return encodings.BytesToString(newString), nil
    73  }
    74  
    75  // WithChildren implements the interface sql.Expression.
    76  func (c *ConvertUsing) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    77  	if len(children) != 1 {
    78  		return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 1)
    79  	}
    80  	return NewConvertUsing(children[0], c.TargetCharSet), nil
    81  }
    82  
    83  // CollationCoercibility implements the interface sql.CollationCoercible.
    84  func (c *ConvertUsing) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    85  	return c.TargetCharSet.DefaultCollation(), 2
    86  }