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count_distinct.go
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count_distinct.go
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// Copyright 2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package aggregation
import (
"fmt"
"github.com/gabereiser/go-mysql-server/sql/expression"
"github.com/gabereiser/go-mysql-server/sql/transform"
"github.com/gabereiser/go-mysql-server/sql/types"
"github.com/gabereiser/go-mysql-server/sql"
)
type CountDistinct struct {
expression.NaryExpression
window *sql.WindowDefinition
typ sql.Type
}
var _ sql.FunctionExpression = (*CountDistinct)(nil)
var _ sql.Aggregation = (*CountDistinct)(nil)
var _ sql.WindowAdaptableExpression = (*CountDistinct)(nil)
func NewCountDistinct(exprs ...sql.Expression) *CountDistinct {
return &CountDistinct{
NaryExpression: expression.NaryExpression{ChildExpressions: exprs},
}
}
// Type implements the Expression interface.
func (a *CountDistinct) Type() sql.Type {
return types.Int64
}
// IsNullable implements the Expression interface.
func (a *CountDistinct) IsNullable() bool {
return false
}
// Eval implements the Expression interface.
func (a *CountDistinct) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
return nil, ErrEvalUnsupportedOnAggregation.New("CountDistinct")
}
// Children implements the Expression interface.
func (a *CountDistinct) Children() []sql.Expression {
return a.ChildExpressions
}
// WithChildren implements the Expression interface.
func (a *CountDistinct) WithChildren(children ...sql.Expression) (sql.Expression, error) {
return NewCountDistinct(children...), nil
}
// FunctionName implements the FunctionExpression interface.
func (a *CountDistinct) FunctionName() string {
return "CountDistinct"
}
// Description implements the FunctionExpression interface.
func (a *CountDistinct) Description() string {
return "returns the number of distinct values in a result set."
}
// NewBuffer implements the Aggregation interface.
func (a *CountDistinct) NewBuffer() (sql.AggregationBuffer, error) {
exprs := make([]sql.Expression, len(a.ChildExpressions))
for i, expr := range a.ChildExpressions {
child, err := transform.Clone(expr)
if err != nil {
return nil, err
}
exprs[i] = child
}
return NewCountDistinctBuffer(exprs), nil
}
// WithWindow implements the Aggregation interface.
func (a *CountDistinct) WithWindow(window *sql.WindowDefinition) (sql.Aggregation, error) {
na := *a
na.window = window
return &na, nil
}
// Window implements the Aggregation interface.
func (a *CountDistinct) Window() *sql.WindowDefinition {
return a.window
}
// String implements the ValueStats interface.
func (a *CountDistinct) String() string {
return fmt.Sprintf("COUNTDISTINCT(%s)", a.ChildExpressions)
}
// NewWindowFunction implements the WindowAdaptableExpression interface.
func (a *CountDistinct) NewWindowFunction() (sql.WindowFunction, error) {
child, err := transform.Clone(a.NaryExpression.ChildExpressions[0])
if err != nil {
return nil, err
}
return NewCountDistinctAgg(child).WithWindow(a.Window())
}