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variables.go
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variables.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 expression
import (
"fmt"
"github.com/Rock-liyi/p2pdb-store/sql"
)
// SystemVar is an expression that returns the value of a system variable. It's also used as the expression on the left
// hand side of a SET statement for a system variable.
type SystemVar struct {
Name string
Scope sql.SystemVariableScope
}
// NewSystemVar creates a new SystemVar expression.
func NewSystemVar(name string, scope sql.SystemVariableScope) *SystemVar {
return &SystemVar{name, scope}
}
// Children implements the sql.Expression interface.
func (v *SystemVar) Children() []sql.Expression { return nil }
// Eval implements the sql.Expression interface.
func (v *SystemVar) Eval(ctx *sql.Context, _ sql.Row) (interface{}, error) {
switch v.Scope {
case sql.SystemVariableScope_Session:
val, err := ctx.GetSessionVariable(ctx, v.Name)
if err != nil {
return nil, err
}
return val, nil
case sql.SystemVariableScope_Global:
_, val, ok := sql.SystemVariables.GetGlobal(v.Name)
if !ok {
return nil, sql.ErrUnknownSystemVariable.New(v.Name)
}
return val, nil
default: // should never happen
return nil, fmt.Errorf("unknown scope `%v` on system variable `%s`", v.Scope, v.Name)
}
}
// Type implements the sql.Expression interface.
func (v *SystemVar) Type() sql.Type {
if sysVar, _, ok := sql.SystemVariables.GetGlobal(v.Name); ok {
return sysVar.Type
}
return sql.Null
}
// IsNullable implements the sql.Expression interface.
func (v *SystemVar) IsNullable() bool { return false }
// Resolved implements the sql.Expression interface.
func (v *SystemVar) Resolved() bool { return true }
// String implements the sql.Expression interface.
func (v *SystemVar) String() string {
switch v.Scope {
case sql.SystemVariableScope_Session:
return fmt.Sprintf("@@SESSION.%s", v.Name)
case sql.SystemVariableScope_Global:
return fmt.Sprintf("@@GLOBAL.%s", v.Name)
default: // should never happen
return fmt.Sprintf("@@UNKNOWN(%v).%s", v.Scope, v.Name)
}
}
// WithChildren implements the Expression interface.
func (v *SystemVar) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 0 {
return nil, sql.ErrInvalidChildrenNumber.New(v, len(children), 0)
}
return v, nil
}
// UserVar is an expression that returns the value of a user variable. It's also used as the expression on the left hand
// side of a SET statement for a user var.
type UserVar struct {
Name string
}
// NewUserVar creates a new UserVar expression.
func NewUserVar(name string) *UserVar {
return &UserVar{name}
}
// Children implements the sql.Expression interface.
func (v *UserVar) Children() []sql.Expression { return nil }
// Eval implements the sql.Expression interface.
func (v *UserVar) Eval(ctx *sql.Context, _ sql.Row) (interface{}, error) {
_, val, err := ctx.GetUserVariable(ctx, v.Name)
if err != nil {
return nil, err
}
return val, nil
}
// Type implements the sql.Expression interface.
// TODO: type checking based on type of user var
func (v *UserVar) Type() sql.Type { return sql.Boolean }
// IsNullable implements the sql.Expression interface.
func (v *UserVar) IsNullable() bool { return true }
// Resolved implements the sql.Expression interface.
func (v *UserVar) Resolved() bool { return true }
// String implements the sql.Expression interface.
func (v *UserVar) String() string { return "@" + v.Name }
// WithChildren implements the Expression interface.
func (v *UserVar) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 0 {
return nil, sql.ErrInvalidChildrenNumber.New(v, len(children), 0)
}
return v, nil
}