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expand_stars.go
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expand_stars.go
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// Copyright 2020-2021 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 analyzer
import (
"strings"
"github.com/gabereiser/go-mysql-server/sql/expression/function/aggregation"
"github.com/gabereiser/go-mysql-server/sql/transform"
"github.com/gabereiser/go-mysql-server/sql/types"
"github.com/gabereiser/go-mysql-server/sql"
"github.com/gabereiser/go-mysql-server/sql/expression"
"github.com/gabereiser/go-mysql-server/sql/plan"
)
// expandStars replaces star expressions into lists of concrete column expressions
func expandStars(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope, sel RuleSelector) (sql.Node, transform.TreeIdentity, error) {
span, ctx := ctx.Span("expand_stars")
defer span.End()
scopeLen := len(scope.Schema())
return transform.Node(n, func(n sql.Node) (sql.Node, transform.TreeIdentity, error) {
if n.Resolved() {
return n, transform.SameTree, nil
}
switch n := n.(type) {
case *plan.Project:
if !n.Child.Resolved() {
return n, transform.SameTree, nil
}
expanded, same, err := expandStarsForExpressions(a, n.Projections, n.Child, scopeLen)
if err != nil {
return nil, transform.SameTree, err
}
if same {
return n, transform.SameTree, nil
}
return plan.NewProject(expanded, n.Child), transform.NewTree, nil
case *plan.GroupBy:
if !n.Child.Resolved() {
return n, transform.SameTree, nil
}
expanded, same, err := expandStarsForExpressions(a, n.SelectedExprs, n.Child, scopeLen)
if err != nil {
return nil, transform.SameTree, err
}
if same {
return n, transform.SameTree, nil
}
return plan.NewGroupBy(expanded, n.GroupByExprs, n.Child), transform.NewTree, nil
case *plan.Window:
if !n.Child.Resolved() {
return n, transform.SameTree, nil
}
expanded, same, err := expandStarsForExpressions(a, n.SelectExprs, n.Child, scopeLen)
if err != nil {
return nil, transform.SameTree, err
}
if same {
return n, transform.SameTree, nil
}
return plan.NewWindow(expanded, n.Child), transform.NewTree, nil
default:
return n, transform.SameTree, nil
}
})
}
func expandStarsForExpressions(a *Analyzer, exprs []sql.Expression, n sql.Node, scopeLen int) ([]sql.Expression, transform.TreeIdentity, error) {
schema := n.Schema()
var expressions []sql.Expression
same := transform.SameTree
for _, e := range exprs {
if star, ok := e.(*expression.Star); ok {
if dt, ok := n.(*plan.ResolvedTable); ok && plan.IsDualTable(dt.Table) {
return nil, transform.SameTree, sql.ErrNoTablesUsed.New()
}
same = transform.NewTree
var exprs []sql.Expression
for i, col := range schema {
lowerSource := strings.ToLower(col.Source)
lowerTable := strings.ToLower(star.Table)
if star.Table == "" || lowerTable == lowerSource {
exprs = append(exprs, expression.NewGetFieldWithTable(
scopeLen+i, col.Type, col.Source, col.Name, col.Nullable,
))
}
}
if len(exprs) == 0 && star.Table != "" {
return nil, false, sql.ErrTableNotFound.New(star.Table)
}
expressions = append(expressions, exprs...)
} else {
expressions = append(expressions, e)
}
}
a.Log("resolved * to expressions %s", expressions)
return expressions, same, nil
}
// replaceCountStar replaces count(*) expressions with count(1) expressions, which are semantically equivalent and
// lets us prune all the unused columns from the target tables.
func replaceCountStar(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope, sel RuleSelector) (sql.Node, transform.TreeIdentity, error) {
if plan.IsDDLNode(n) {
return n, transform.SameTree, nil
}
return transform.NodeExprs(n, func(e sql.Expression) (sql.Expression, transform.TreeIdentity, error) {
if count, ok := e.(*aggregation.Count); ok {
if _, ok := count.Child.(*expression.Star); ok {
count, err := count.WithChildren(expression.NewLiteral(int64(1), types.Int64))
if err != nil {
return nil, transform.SameTree, err
}
return count, transform.NewTree, nil
}
}
return e, transform.SameTree, nil
})
}