github.com/dolthub/go-mysql-server@v0.18.0/sql/expression/function/collation.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 function
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"github.com/dolthub/go-mysql-server/sql/types"
    21  
    22  	"github.com/dolthub/go-mysql-server/sql"
    23  	"github.com/dolthub/go-mysql-server/sql/expression"
    24  )
    25  
    26  // Collation is a function that returns the collation of the inner expression.
    27  type Collation struct {
    28  	expression.UnaryExpression
    29  }
    30  
    31  var _ sql.FunctionExpression = (*Collation)(nil)
    32  var _ sql.CollationCoercible = (*Collation)(nil)
    33  
    34  // NewCollation creates a new Collation expression.
    35  func NewCollation(e sql.Expression) sql.Expression {
    36  	return &Collation{expression.UnaryExpression{Child: e}}
    37  }
    38  
    39  // FunctionName implements sql.FunctionExpression
    40  func (c *Collation) FunctionName() string {
    41  	return "collation"
    42  }
    43  
    44  // Description implements sql.FunctionExpression
    45  func (c *Collation) Description() string {
    46  	return "Returns the collation of the inner expression"
    47  }
    48  
    49  // Eval implements the sql.Expression.
    50  func (c *Collation) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    51  	val, err := c.Child.Eval(ctx, row)
    52  	if err != nil {
    53  		return nil, err
    54  	}
    55  	// If the value is nil, then we return 'binary'
    56  	if val == nil {
    57  		return sql.Collation_binary.Name(), nil
    58  	}
    59  	// Otherwise, we return the collation calculated from the expression
    60  	collation, _ := sql.GetCoercibility(ctx, c.Child)
    61  	return collation.Name(), nil
    62  }
    63  
    64  // String implements the fmt.Stringer interface.
    65  func (c *Collation) String() string {
    66  	return fmt.Sprintf("%s(%s)", c.FunctionName(), c.Child.String())
    67  }
    68  
    69  // WithChildren implements the Expression interface.
    70  func (c *Collation) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    71  	if len(children) != 1 {
    72  		return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 1)
    73  	}
    74  	return NewCollation(children[0]), nil
    75  }
    76  
    77  // Type implements the Expression interface.
    78  func (c *Collation) Type() sql.Type {
    79  	return types.LongText
    80  }
    81  
    82  // CollationCoercibility implements the interface sql.CollationCoercible.
    83  func (*Collation) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    84  	return sql.Collation_utf8mb3_general_ci, 4
    85  }
    86  
    87  // Coercibility is a function that returns the coercibility of the inner expression.
    88  type Coercibility struct {
    89  	expression.UnaryExpression
    90  }
    91  
    92  var _ sql.FunctionExpression = (*Coercibility)(nil)
    93  var _ sql.CollationCoercible = (*Coercibility)(nil)
    94  
    95  // NewCoercibility creates a new Coercibility expression.
    96  func NewCoercibility(e sql.Expression) sql.Expression {
    97  	return &Coercibility{expression.UnaryExpression{Child: e}}
    98  }
    99  
   100  // FunctionName implements sql.FunctionExpression
   101  func (c *Coercibility) FunctionName() string {
   102  	return "coercibility"
   103  }
   104  
   105  // Description implements sql.FunctionExpression
   106  func (c *Coercibility) Description() string {
   107  	return "Returns the coercibility of the inner expression"
   108  }
   109  
   110  // Eval implements the sql.Expression.
   111  func (c *Coercibility) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
   112  	val, err := c.Child.Eval(ctx, row)
   113  	if err != nil {
   114  		return nil, err
   115  	}
   116  	// If the value is nil, then we return 'binary'
   117  	if val == nil {
   118  		return 6, nil
   119  	}
   120  	// Otherwise, we return the collation calculated from the expression
   121  	_, coercibility := sql.GetCoercibility(ctx, c.Child)
   122  	return coercibility, nil
   123  }
   124  
   125  // String implements the fmt.Stringer interface.
   126  func (c *Coercibility) String() string {
   127  	return fmt.Sprintf("%s(%s)", c.FunctionName(), c.Child.String())
   128  }
   129  
   130  // WithChildren implements the Expression interface.
   131  func (c *Coercibility) WithChildren(children ...sql.Expression) (sql.Expression, error) {
   132  	if len(children) != 1 {
   133  		return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 1)
   134  	}
   135  	return NewCoercibility(children[0]), nil
   136  }
   137  
   138  // Type implements the Expression interface.
   139  func (c *Coercibility) Type() sql.Type {
   140  	return types.Int8
   141  }
   142  
   143  // CollationCoercibility implements the interface sql.CollationCoercible.
   144  func (*Coercibility) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
   145  	return sql.Collation_binary, 5
   146  }