96 lines
2.4 KiB
Go
96 lines
2.4 KiB
Go
// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package expression
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import (
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"strings"
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"github.com/juju/errors"
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"github.com/pingcap/tidb/context"
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"github.com/pingcap/tidb/sessionctx/variable"
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)
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var (
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_ Expression = (*Variable)(nil)
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)
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// Variable is the expression for variable.
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type Variable struct {
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// Name is the variable name.
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Name string
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// IsGlobal indicates whether this variable is global.
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IsGlobal bool
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// IsSystem indicates whether this variable is a global variable in current session.
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IsSystem bool
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}
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// Clone implements the Expression Clone interface.
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func (v *Variable) Clone() Expression {
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newVar := *v
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return &newVar
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}
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// IsStatic implements the Expression IsStatic interface, always returns false.
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func (v *Variable) IsStatic() bool {
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return false
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}
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// String implements the Expression String interface.
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func (v *Variable) String() string {
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if !v.IsSystem {
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return "@" + v.Name
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}
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if v.IsGlobal {
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return "@@GLOBAL." + v.Name
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}
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return "@@" + v.Name
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}
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// Eval implements the Expression Eval interface.
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func (v *Variable) Eval(ctx context.Context, args map[interface{}]interface{}) (interface{}, error) {
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name := strings.ToLower(v.Name)
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sessionVars := variable.GetSessionVars(ctx)
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if !v.IsSystem {
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// user vars
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if value, ok := sessionVars.Users[name]; ok {
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return value, nil
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}
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// select null user vars is permitted.
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return nil, nil
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}
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_, ok := variable.SysVars[name]
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if !ok {
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// select null sys vars is not permitted
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return nil, errors.Errorf("Unknown system variable '%s'", name)
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}
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if !v.IsGlobal {
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if value, ok := sessionVars.Systems[name]; ok {
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return value, nil
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}
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}
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value, err := ctx.(variable.GlobalSysVarAccessor).GetGlobalSysVar(ctx, name)
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if err != nil {
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return nil, errors.Trace(err)
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}
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return value, nil
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}
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// Accept implements Expression Accept interface.
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func (v *Variable) Accept(visitor Visitor) (Expression, error) {
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return visitor.VisitVariable(v)
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}
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