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

     1  // Copyright 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 aggregation
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"github.com/dolthub/go-mysql-server/sql/expression"
    21  	"github.com/dolthub/go-mysql-server/sql/transform"
    22  	"github.com/dolthub/go-mysql-server/sql/types"
    23  
    24  	"github.com/dolthub/go-mysql-server/sql"
    25  )
    26  
    27  type CountDistinct struct {
    28  	expression.NaryExpression
    29  	window *sql.WindowDefinition
    30  	typ    sql.Type
    31  	id     sql.ColumnId
    32  }
    33  
    34  var _ sql.FunctionExpression = (*CountDistinct)(nil)
    35  var _ sql.Aggregation = (*CountDistinct)(nil)
    36  var _ sql.WindowAdaptableExpression = (*CountDistinct)(nil)
    37  var _ sql.CollationCoercible = (*CountDistinct)(nil)
    38  
    39  func NewCountDistinct(exprs ...sql.Expression) *CountDistinct {
    40  	return &CountDistinct{
    41  		NaryExpression: expression.NaryExpression{ChildExpressions: exprs},
    42  	}
    43  }
    44  
    45  // Type implements the Expression interface.
    46  func (a *CountDistinct) Type() sql.Type {
    47  	return types.Int64
    48  }
    49  
    50  // CollationCoercibility implements the interface sql.CollationCoercible.
    51  func (*CountDistinct) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    52  	return sql.Collation_binary, 5
    53  }
    54  
    55  // IsNullable implements the Expression interface.
    56  func (a *CountDistinct) IsNullable() bool {
    57  	return false
    58  }
    59  
    60  // Id implements the Aggregation interface
    61  func (a *CountDistinct) Id() sql.ColumnId {
    62  	return a.id
    63  }
    64  
    65  // WithId implements the Aggregation interface
    66  func (a *CountDistinct) WithId(id sql.ColumnId) sql.IdExpression {
    67  	ret := *a
    68  	ret.id = id
    69  	return &ret
    70  }
    71  
    72  // Eval implements the Expression interface.
    73  func (a *CountDistinct) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    74  	return nil, ErrEvalUnsupportedOnAggregation.New("CountDistinct")
    75  }
    76  
    77  // Children implements the Expression interface.
    78  func (a *CountDistinct) Children() []sql.Expression {
    79  	return a.ChildExpressions
    80  }
    81  
    82  // WithChildren implements the Expression interface.
    83  func (a *CountDistinct) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    84  	return NewCountDistinct(children...), nil
    85  }
    86  
    87  // FunctionName implements the FunctionExpression interface.
    88  func (a *CountDistinct) FunctionName() string {
    89  	return "CountDistinct"
    90  }
    91  
    92  // Description implements the FunctionExpression interface.
    93  func (a *CountDistinct) Description() string {
    94  	return "returns the number of distinct values in a result set."
    95  }
    96  
    97  // NewBuffer implements the Aggregation interface.
    98  func (a *CountDistinct) NewBuffer() (sql.AggregationBuffer, error) {
    99  	exprs := make([]sql.Expression, len(a.ChildExpressions))
   100  	for i, expr := range a.ChildExpressions {
   101  		child, err := transform.Clone(expr)
   102  		if err != nil {
   103  			return nil, err
   104  		}
   105  		exprs[i] = child
   106  	}
   107  	return NewCountDistinctBuffer(exprs), nil
   108  }
   109  
   110  // WithWindow implements the Aggregation interface.
   111  func (a *CountDistinct) WithWindow(window *sql.WindowDefinition) sql.WindowAdaptableExpression {
   112  	na := *a
   113  	na.window = window
   114  	return &na
   115  }
   116  
   117  // Window implements the Aggregation interface.
   118  func (a *CountDistinct) Window() *sql.WindowDefinition {
   119  	return a.window
   120  }
   121  
   122  // String implements the ValueStats interface.
   123  func (a *CountDistinct) String() string {
   124  	return fmt.Sprintf("COUNTDISTINCT(%s)", a.ChildExpressions)
   125  }
   126  
   127  // NewWindowFunction implements the WindowAdaptableExpression interface.
   128  func (a *CountDistinct) NewWindowFunction() (sql.WindowFunction, error) {
   129  	child, err := transform.Clone(a.NaryExpression.ChildExpressions[0])
   130  	if err != nil {
   131  		return nil, err
   132  	}
   133  	return NewCountDistinctAgg(child).WithWindow(a.Window())
   134  }