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

     1  // Copyright 2024 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 function
    16  
    17  import (
    18  	"fmt"
    19  	"strings"
    20  
    21  	"github.com/dolthub/go-mysql-server/sql"
    22  	"github.com/dolthub/go-mysql-server/sql/types"
    23  )
    24  
    25  // Elt joins several strings together.
    26  type Elt struct {
    27  	args []sql.Expression
    28  }
    29  
    30  var _ sql.FunctionExpression = (*Elt)(nil)
    31  var _ sql.CollationCoercible = (*Elt)(nil)
    32  
    33  // NewElt creates a new Elt UDF.
    34  func NewElt(args ...sql.Expression) (sql.Expression, error) {
    35  	if len(args) < 2 {
    36  		return nil, sql.ErrInvalidArgumentNumber.New("ELT", "2 or more", len(args))
    37  	}
    38  
    39  	return &Elt{args}, nil
    40  }
    41  
    42  // FunctionName implements sql.FunctionExpression
    43  func (e *Elt) FunctionName() string {
    44  	return "elt"
    45  }
    46  
    47  // Description implements sql.FunctionExpression
    48  func (e *Elt) Description() string {
    49  	return "returns the string at index number."
    50  }
    51  
    52  // Type implements the Expression interface.
    53  func (e *Elt) Type() sql.Type {
    54  	return types.LongText
    55  }
    56  
    57  // CollationCoercibility implements the interface sql.CollationCoercible.
    58  func (e *Elt) CollationCoercibility(ctx *sql.Context) (sql.CollationID, byte) {
    59  	if len(e.args) == 0 {
    60  		return sql.Collation_binary, 6
    61  	}
    62  	collation, coercibility := sql.GetCoercibility(ctx, e.args[0])
    63  	for i := 1; i < len(e.args); i++ {
    64  		nextCollation, nextCoercibility := sql.GetCoercibility(ctx, e.args[i])
    65  		collation, coercibility = sql.ResolveCoercibility(collation, coercibility, nextCollation, nextCoercibility)
    66  	}
    67  	return collation, coercibility
    68  }
    69  
    70  // IsNullable implements the Expression interface.
    71  func (e *Elt) IsNullable() bool {
    72  	return true
    73  }
    74  
    75  // String implements the Stringer interface.
    76  func (e *Elt) String() string {
    77  	var args = make([]string, len(e.args))
    78  	for i, arg := range e.args {
    79  		args[i] = arg.String()
    80  	}
    81  	return fmt.Sprintf("%s(%s)", e.FunctionName(), strings.Join(args, ","))
    82  }
    83  
    84  // WithChildren implements the Expression interface.
    85  func (*Elt) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    86  	return NewElt(children...)
    87  }
    88  
    89  // Resolved implements the Expression interface.
    90  func (e *Elt) Resolved() bool {
    91  	for _, arg := range e.args {
    92  		if !arg.Resolved() {
    93  			return false
    94  		}
    95  	}
    96  	return true
    97  }
    98  
    99  // Children implements the Expression interface.
   100  func (e *Elt) Children() []sql.Expression {
   101  	return e.args
   102  }
   103  
   104  // Eval implements the Expression interface.
   105  func (e *Elt) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
   106  	if e.args[0] == nil {
   107  		return nil, nil
   108  	}
   109  
   110  	index, err := e.args[0].Eval(ctx, row)
   111  	if err != nil {
   112  		return nil, err
   113  	}
   114  
   115  	if index == nil {
   116  		return nil, nil
   117  	}
   118  
   119  	indexInt, _, err := types.Int64.Convert(index)
   120  	if err != nil {
   121  		// TODO: truncate
   122  		ctx.Warn(1292, "Truncated incorrect INTEGER value: '%v'", index)
   123  		indexInt = int64(0)
   124  	}
   125  
   126  	idx := int(indexInt.(int64))
   127  	if idx <= 0 || idx >= len(e.args) {
   128  		return nil, nil
   129  	}
   130  
   131  	str, err := e.args[idx].Eval(ctx, row)
   132  	if err != nil {
   133  		return nil, err
   134  	}
   135  
   136  	res, _, err := types.Text.Convert(str)
   137  	if err != nil {
   138  		return nil, err
   139  	}
   140  
   141  	return res, nil
   142  }