func (e *Evaluator) variable(v *ast.VariableExpr) bool {
name := strings.ToLower(v.Name)
sessionVars := variable.GetSessionVars(e.ctx)
globalVars := variable.GetGlobalVarAccessor(e.ctx)
if !v.IsSystem {
// user vars
if value, ok := sessionVars.Users[name]; ok {
v.SetValue(value)
return true
}
// select null user vars is permitted.
v.SetValue(nil)
return true
}
_, ok := variable.SysVars[name]
if !ok {
// select null sys vars is not permitted
e.err = variable.UnknownSystemVar.Gen("Unknown system variable '%s'", name)
return false
}
if !v.IsGlobal {
if value, ok := sessionVars.Systems[name]; ok {
v.SetValue(value)
return true
}
}
value, err := globalVars.GetGlobalSysVar(e.ctx, name)
if err != nil {
e.err = errors.Trace(err)
return false
}
v.SetValue(value)
return true
}
