github.com/dolthub/go-mysql-server@v0.18.0/sql/expression/function/if.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/types"
    22  )
    23  
    24  // If function returns the second value if the first is true, the third value otherwise.
    25  type If struct {
    26  	expr    sql.Expression
    27  	ifTrue  sql.Expression
    28  	ifFalse sql.Expression
    29  }
    30  
    31  var _ sql.FunctionExpression = (*If)(nil)
    32  var _ sql.CollationCoercible = (*If)(nil)
    33  
    34  // FunctionName implements sql.FunctionExpression
    35  func (f *If) FunctionName() string {
    36  	return "if"
    37  }
    38  
    39  // Description implements sql.FunctionExpression
    40  func (f *If) Description() string {
    41  	return "if expr evaluates to true, returns ifTrue. Otherwise returns ifFalse."
    42  }
    43  
    44  func (f *If) Resolved() bool {
    45  	return f.expr.Resolved() && f.ifTrue.Resolved() && f.ifFalse.Resolved()
    46  }
    47  
    48  func (f *If) Children() []sql.Expression {
    49  	return []sql.Expression{
    50  		f.expr, f.ifTrue, f.ifFalse,
    51  	}
    52  }
    53  
    54  // NewIf returns a new IF UDF
    55  func NewIf(expr, ifTrue, ifFalse sql.Expression) sql.Expression {
    56  	return &If{
    57  		expr:    expr,
    58  		ifTrue:  ifTrue,
    59  		ifFalse: ifFalse,
    60  	}
    61  }
    62  
    63  // Eval implements the Expression interface.
    64  func (f *If) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    65  	e, err := f.expr.Eval(ctx, row)
    66  	if err != nil {
    67  		return nil, err
    68  	}
    69  
    70  	var asBool bool
    71  	if e == nil {
    72  		asBool = false
    73  	} else {
    74  		asBool, err = sql.ConvertToBool(ctx, e)
    75  		if err != nil {
    76  			return nil, err
    77  		}
    78  	}
    79  
    80  	if asBool {
    81  		return f.ifTrue.Eval(ctx, row)
    82  	} else {
    83  		return f.ifFalse.Eval(ctx, row)
    84  	}
    85  }
    86  
    87  // Type implements the Expression interface.
    88  func (f *If) Type() sql.Type {
    89  	// if either type is string type, this should be a string type, regardless need to promote
    90  	typ1 := f.ifTrue.Type()
    91  	typ2 := f.ifFalse.Type()
    92  	if types.IsText(typ1) || types.IsText(typ2) {
    93  		return types.Text
    94  	}
    95  
    96  	if typ1 == types.Null {
    97  		return typ2.Promote()
    98  	}
    99  	return typ1.Promote()
   100  }
   101  
   102  // CollationCoercibility implements the interface sql.CollationCoercible.
   103  func (f *If) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
   104  	// We would need to evaluate the condition to return the correct result here, so we'll copy
   105  	// Type and just return the true result
   106  	return sql.GetCoercibility(ctx, f.ifTrue)
   107  }
   108  
   109  // IsNullable implements the Expression interface.
   110  func (f *If) IsNullable() bool {
   111  	return f.ifTrue.IsNullable()
   112  }
   113  
   114  func (f *If) String() string {
   115  	return fmt.Sprintf("%s(%s,%s,%s)", f.FunctionName(), f.expr, f.ifTrue, f.ifFalse)
   116  }
   117  
   118  // WithChildren implements the Expression interface.
   119  func (f *If) WithChildren(children ...sql.Expression) (sql.Expression, error) {
   120  	if len(children) != 3 {
   121  		return nil, sql.ErrInvalidChildrenNumber.New(f, len(children), 3)
   122  	}
   123  	return NewIf(children[0], children[1], children[2]), nil
   124  }