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// Copyright 2019 PingCAP, 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package util
import (
"github.com/pingcap/parser/ast"
"github.com/pingcap/parser/model"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/kv"
"github.com/pingcap/tidb/sessionctx"
"github.com/pingcap/tidb/types"
"github.com/pingcap/tidb/util/collate"
"github.com/pingcap/tidb/util/ranger"
)
// AccessPath indicates the way we access a table: by using single index, or by using multiple indexes,
// or just by using table scan.
type AccessPath struct {
Index *model.IndexInfo
FullIdxCols []*expression.Column
FullIdxColLens []int
IdxCols []*expression.Column
IdxColLens []int
Ranges []*ranger.Range
// CountAfterAccess is the row count after we apply range seek and before we use other filter to filter data.
CountAfterAccess float64
// CountAfterIndex is the row count after we apply filters on index and before we apply the table filters.
CountAfterIndex float64
AccessConds []expression.Expression
EqCondCount int
EqOrInCondCount int
IndexFilters []expression.Expression
TableFilters []expression.Expression
// PartialIndexPaths store all index access paths.
// If there are extra filters, store them in TableFilters.
PartialIndexPaths []*AccessPath
StoreType kv.StoreType
IsDNFCond bool
// IsTablePath indicates whether this path is table path.
IsTablePath bool
// IsTiFlashGlobalRead indicates whether this path is a remote read path for tiflash
IsTiFlashGlobalRead bool
// Forced means this path is generated by `use/force index()`.
Forced bool
PkCol *expression.Column
}
// SplitCorColAccessCondFromFilters move the necessary filter in the form of index_col = corrlated_col to access conditions.
func (path *AccessPath) SplitCorColAccessCondFromFilters(ctx sessionctx.Context, eqOrInCount int) (access, remained []expression.Expression) {
access = make([]expression.Expression, len(path.IdxCols)-eqOrInCount)
used := make([]bool, len(path.TableFilters))
for i := eqOrInCount; i < len(path.IdxCols); i++ {
matched := false
for j, filter := range path.TableFilters {
if used[j] || !isColEqCorColOrConstant(ctx, filter, path.IdxCols[i]) {
continue
}
matched = true
access[i-eqOrInCount] = filter
if path.IdxColLens[i] == types.UnspecifiedLength {
used[j] = true
}
break
}
if !matched {
access = access[:i-eqOrInCount]
break
}
}
for i, ok := range used {
if !ok {
remained = append(remained, path.TableFilters[i])
}
}
return access, remained
}
// isColEqCorColOrConstant checks if the expression is a eq function that one side is constant or correlated column
// and another is column.
func isColEqCorColOrConstant(ctx sessionctx.Context, filter expression.Expression, col *expression.Column) bool {
f, ok := filter.(*expression.ScalarFunction)
if !ok || f.FuncName.L != ast.EQ {
return false
}
_, collation := f.CharsetAndCollation(ctx)
if c, ok := f.GetArgs()[0].(*expression.Column); ok {
if c.RetType.EvalType() == types.ETString && !collate.CompatibleCollate(collation, c.RetType.Collate) {
return false
}
if _, ok := f.GetArgs()[1].(*expression.Constant); ok {
if col.Equal(nil, c) {
return true
}
}
if _, ok := f.GetArgs()[1].(*expression.CorrelatedColumn); ok {
if col.Equal(nil, c) {
return true
}
}
}
if c, ok := f.GetArgs()[1].(*expression.Column); ok {
if c.RetType.EvalType() == types.ETString && !collate.CompatibleCollate(collation, c.RetType.Collate) {
return false
}
if _, ok := f.GetArgs()[0].(*expression.Constant); ok {
if col.Equal(nil, c) {
return true
}
}
if _, ok := f.GetArgs()[0].(*expression.CorrelatedColumn); ok {
if col.Equal(nil, c) {
return true
}
}
}
return false
}