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resolve_unions.go
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/
resolve_unions.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 (
"reflect"
"gopkg.in/src-d/go-errors.v1"
"github.com/Rock-liyi/p2pdb-store/sql"
"github.com/Rock-liyi/p2pdb-store/sql/expression"
"github.com/Rock-liyi/p2pdb-store/sql/plan"
)
// resolveUnions resolves the left and right side of a union node in isolation.
func resolveUnions(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope) (sql.Node, error) {
if n.Resolved() {
return n, nil
}
// Procedures explicitly handle unions
if _, ok := n.(*plan.CreateProcedure); ok {
return n, nil
}
return plan.TransformUp(n, func(n sql.Node) (sql.Node, error) {
switch n := n.(type) {
case *plan.Union:
subqueryCtx, cancelFunc := ctx.NewSubContext()
defer cancelFunc()
left, err := a.analyzeThroughBatch(subqueryCtx, n.Left(), scope, "default-rules")
if err != nil {
return nil, err
}
right, err := a.analyzeThroughBatch(subqueryCtx, n.Right(), scope, "default-rules")
if err != nil {
return nil, err
}
return n.WithChildren(StripQueryProcess(left), StripQueryProcess(right))
default:
return n, nil
}
})
}
func finalizeUnions(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope) (sql.Node, error) {
// Procedures explicitly handle unions
if _, ok := n.(*plan.CreateProcedure); ok {
return n, nil
}
return plan.TransformUp(n, func(n sql.Node) (sql.Node, error) {
switch n := n.(type) {
case *plan.Union:
subqueryCtx, cancelFunc := ctx.NewSubContext()
defer cancelFunc()
left, err := a.analyzeStartingAtBatch(subqueryCtx, n.Left(), scope, "default-rules")
if err != nil {
return nil, err
}
right, err := a.analyzeStartingAtBatch(subqueryCtx, n.Right(), scope, "default-rules")
if err != nil {
return nil, err
}
return n.WithChildren(StripQueryProcess(left), StripQueryProcess(right))
default:
return n, nil
}
})
}
var (
// ErrUnionSchemasDifferentLength is returned when the two sides of a
// UNION do not have the same number of columns in their schemas.
ErrUnionSchemasDifferentLength = errors.NewKind(
"cannot union two queries whose schemas are different lengths; left has %d column(s) right has %d column(s).",
)
)
// mergeUnionSchemas determines the narrowest possible shared schema types between the two sides of a union, and
// applies projections the two sides to convert column types as necessary.
func mergeUnionSchemas(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope) (sql.Node, error) {
if !n.Resolved() {
return n, nil
}
return plan.TransformUp(n, func(n sql.Node) (sql.Node, error) {
if u, ok := n.(*plan.Union); ok {
ls, rs := u.Left().Schema(), u.Right().Schema()
if len(ls) != len(rs) {
return nil, ErrUnionSchemasDifferentLength.New(len(ls), len(rs))
}
les, res := make([]sql.Expression, len(ls)), make([]sql.Expression, len(rs))
hasdiff := false
for i := range ls {
les[i] = expression.NewGetFieldWithTable(i, ls[i].Type, ls[i].Source, ls[i].Name, ls[i].Nullable)
res[i] = expression.NewGetFieldWithTable(i, rs[i].Type, rs[i].Source, rs[i].Name, rs[i].Nullable)
if reflect.DeepEqual(ls[i].Type, rs[i].Type) {
continue
}
hasdiff = true
// TODO: Principled type coercion...
les[i] = expression.NewConvert(les[i], expression.ConvertToChar)
res[i] = expression.NewConvert(res[i], expression.ConvertToChar)
// Preserve schema names across the conversion.
les[i] = expression.NewAlias(ls[i].Name, les[i])
res[i] = expression.NewAlias(rs[i].Name, res[i])
}
if hasdiff {
return u.WithChildren(
plan.NewProject(les, u.Left()),
plan.NewProject(res, u.Right()),
)
} else {
return u, nil
}
}
return n, nil
})
}