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

     1  // Copyright 2020-2021 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"
    21  	"github.com/dolthub/go-mysql-server/sql/expression"
    22  	"github.com/dolthub/go-mysql-server/sql/types"
    23  )
    24  
    25  // IfNull function returns the specified value IF the expression is NULL, otherwise return the expression.
    26  type IfNull struct {
    27  	expression.BinaryExpressionStub
    28  }
    29  
    30  var _ sql.FunctionExpression = (*IfNull)(nil)
    31  var _ sql.CollationCoercible = (*IfNull)(nil)
    32  
    33  // NewIfNull returns a new IFNULL UDF
    34  func NewIfNull(ex, value sql.Expression) sql.Expression {
    35  	return &IfNull{
    36  		expression.BinaryExpressionStub{
    37  			LeftChild:  ex,
    38  			RightChild: value,
    39  		},
    40  	}
    41  }
    42  
    43  // FunctionName implements sql.FunctionExpression
    44  func (f *IfNull) FunctionName() string {
    45  	return "ifnull"
    46  }
    47  
    48  // Description implements sql.FunctionExpression
    49  func (f *IfNull) Description() string {
    50  	return "if expr1 is not NULL, it returns expr1; otherwise it returns expr2."
    51  }
    52  
    53  // Eval implements the Expression interface.
    54  func (f *IfNull) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    55  	left, err := f.LeftChild.Eval(ctx, row)
    56  	if err != nil {
    57  		return nil, err
    58  	}
    59  	if left != nil {
    60  		return left, nil
    61  	}
    62  
    63  	right, err := f.RightChild.Eval(ctx, row)
    64  	if err != nil {
    65  		return nil, err
    66  	}
    67  	return right, nil
    68  }
    69  
    70  // Type implements the Expression interface.
    71  func (f *IfNull) Type() sql.Type {
    72  	if types.IsNull(f.LeftChild) {
    73  		if types.IsNull(f.RightChild) {
    74  			return types.Null
    75  		}
    76  		return f.RightChild.Type()
    77  	}
    78  	return f.LeftChild.Type()
    79  }
    80  
    81  // CollationCoercibility implements the interface sql.CollationCoercible.
    82  func (f *IfNull) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    83  	if types.IsNull(f.LeftChild) {
    84  		if types.IsNull(f.RightChild) {
    85  			return sql.Collation_binary, 6
    86  		}
    87  		return sql.GetCoercibility(ctx, f.RightChild)
    88  	}
    89  	return sql.GetCoercibility(ctx, f.LeftChild)
    90  }
    91  
    92  // IsNullable implements the Expression interface.
    93  func (f *IfNull) IsNullable() bool {
    94  	if types.IsNull(f.LeftChild) {
    95  		if types.IsNull(f.RightChild) {
    96  			return true
    97  		}
    98  		return f.RightChild.IsNullable()
    99  	}
   100  	return f.LeftChild.IsNullable()
   101  }
   102  
   103  func (f *IfNull) String() string {
   104  	return fmt.Sprintf("ifnull(%s, %s)", f.LeftChild, f.RightChild)
   105  }
   106  
   107  // WithChildren implements the Expression interface.
   108  func (f *IfNull) WithChildren(children ...sql.Expression) (sql.Expression, error) {
   109  	if len(children) != 2 {
   110  		return nil, sql.ErrInvalidChildrenNumber.New(f, len(children), 2)
   111  	}
   112  	return NewIfNull(children[0], children[1]), nil
   113  }