github.com/dolthub/go-mysql-server@v0.18.0/sql/analyzer/replace_count_star.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 analyzer
    16  
    17  import (
    18  	"github.com/dolthub/go-mysql-server/sql/expression/function/aggregation"
    19  	"github.com/dolthub/go-mysql-server/sql/transform"
    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  	"github.com/dolthub/go-mysql-server/sql/plan"
    25  )
    26  
    27  // replaceCountStar replaces count(*) expressions with count(1) expressions, which are semantically equivalent and
    28  // lets us prune all the unused columns from the target tables.
    29  func replaceCountStar(ctx *sql.Context, a *Analyzer, n sql.Node, scope *plan.Scope, sel RuleSelector) (sql.Node, transform.TreeIdentity, error) {
    30  	if plan.IsDDLNode(n) {
    31  		return n, transform.SameTree, nil
    32  	}
    33  
    34  	return transform.Node(n, func(n sql.Node) (sql.Node, transform.TreeIdentity, error) {
    35  		if agg, ok := n.(*plan.GroupBy); ok {
    36  			if len(agg.SelectedExprs) == 1 && len(agg.GroupByExprs) == 0 {
    37  				child := agg.SelectedExprs[0]
    38  				var cnt *aggregation.Count
    39  				name := ""
    40  				if alias, ok := child.(*expression.Alias); ok {
    41  					cnt, _ = alias.Child.(*aggregation.Count)
    42  					name = alias.Name()
    43  				} else {
    44  					cnt, _ = child.(*aggregation.Count)
    45  					name = child.String()
    46  				}
    47  				if cnt != nil {
    48  					switch cnt.Child.(type) {
    49  					case *expression.Star, *expression.Literal:
    50  						var rt *plan.ResolvedTable
    51  						switch c := agg.Child.(type) {
    52  						case *plan.ResolvedTable:
    53  							rt = c
    54  						case *plan.TableAlias:
    55  							if t, ok := c.Child.(*plan.ResolvedTable); ok {
    56  								rt = t
    57  							}
    58  						}
    59  						if rt != nil && !sql.IsKeyless(rt.Table.Schema()) {
    60  							if statsTable, ok := rt.Table.(sql.StatisticsTable); ok {
    61  								rowCnt, exact, err := statsTable.RowCount(ctx)
    62  								if err == nil && exact {
    63  									return plan.NewProject(
    64  										[]sql.Expression{
    65  											expression.NewAlias(name, expression.NewGetFieldWithTable(int(cnt.Id()), 0, types.Int64, rt.Database().Name(), statsTable.Name(), name, false)).WithId(cnt.Id()),
    66  										},
    67  										plan.NewTableCount(name, rt.SqlDatabase, statsTable, rowCnt, cnt.Id()),
    68  									), transform.NewTree, nil
    69  								}
    70  							}
    71  						}
    72  					}
    73  				}
    74  			}
    75  		}
    76  
    77  		return transform.NodeExprs(n, func(e sql.Expression) (sql.Expression, transform.TreeIdentity, error) {
    78  			if count, ok := e.(*aggregation.Count); ok {
    79  				if _, ok := count.Child.(*expression.Star); ok {
    80  					count, err := count.WithChildren(expression.NewLiteral(int64(1), types.Int64))
    81  					if err != nil {
    82  						return nil, transform.SameTree, err
    83  					}
    84  					return count, transform.NewTree, nil
    85  				}
    86  			}
    87  
    88  			return e, transform.SameTree, nil
    89  		})
    90  	})
    91  }