Golang Datum.ToString方法代碼示例

// SetSystemVar sets a system variable.
func (s *SessionVars) SetSystemVar(key string, value types.Datum) error {
	key = strings.ToLower(key)
	if value.IsNull() {
		if key != characterSetResults {
			return errCantSetToNull
		}
		delete(s.systems, key)
		return nil
	}
	sVal, err := value.ToString()
	if err != nil {
		return errors.Trace(err)
	}
	if key == sqlMode {
		sVal = strings.ToUpper(sVal)
		if strings.Contains(sVal, "STRICT_TRANS_TABLES") || strings.Contains(sVal, "STRICT_ALL_TABLES") {
			s.StrictSQLMode = true
		} else {
			s.StrictSQLMode = false
		}
	} else if key == TiDBSnapshot {
		err = s.setSnapshotTS(sVal)
		if err != nil {
			return errors.Trace(err)
		}
	}
	s.systems[key] = sVal
	return nil
}

// SetSystemVar sets system variable and updates SessionVars states.
func SetSystemVar(vars *variable.SessionVars, name string, value types.Datum) error {
	name = strings.ToLower(name)
	if value.IsNull() {
		if name != variable.CharacterSetResults {
			return variable.ErrCantSetToNull
		}
		delete(vars.Systems, name)
		return nil
	}
	sVal, err := value.ToString()
	if err != nil {
		return errors.Trace(err)
	}
	switch name {
	case variable.SQLModeVar:
		sVal = strings.ToUpper(sVal)
		if strings.Contains(sVal, "STRICT_TRANS_TABLES") || strings.Contains(sVal, "STRICT_ALL_TABLES") {
			vars.StrictSQLMode = true
		} else {
			vars.StrictSQLMode = false
		}
	case variable.TiDBSnapshot:
		err = setSnapshotTS(vars, sVal)
		if err != nil {
			return errors.Trace(err)
		}
	case variable.AutocommitVar:
		isAutocommit := strings.EqualFold(sVal, "ON") || sVal == "1"
		vars.SetStatusFlag(mysql.ServerStatusAutocommit, isAutocommit)
	case variable.TiDBSkipConstraintCheck:
		vars.SkipConstraintCheck = (sVal == "1")
	}
	vars.Systems[name] = sVal
	return nil
}

func (er *expressionRewriter) rewriteVariable(v *ast.VariableExpr) bool {
	stkLen := len(er.ctxStack)
	name := strings.ToLower(v.Name)
	sessionVars := variable.GetSessionVars(er.b.ctx)
	globalVars := variable.GetGlobalVarAccessor(er.b.ctx)
	if !v.IsSystem {
		var d types.Datum
		var err error
		if v.Value != nil {
			d, err = er.ctxStack[stkLen-1].Eval(nil, er.b.ctx)
			if err != nil {
				er.err = errors.Trace(err)
				return false
			}
			er.ctxStack = er.ctxStack[:stkLen-1]
		}
		if !d.IsNull() {
			strVal, err := d.ToString()
			if err != nil {
				er.err = errors.Trace(err)
				return false
			}
			sessionVars.Users[name] = strings.ToLower(strVal)
			er.ctxStack = append(er.ctxStack, datumToConstant(d, mysql.TypeString))
		} else if value, ok := sessionVars.Users[name]; ok {
			er.ctxStack = append(er.ctxStack, datumToConstant(types.NewStringDatum(value), mysql.TypeString))
		} else {
			// select null user vars is permitted.
			er.ctxStack = append(er.ctxStack, &expression.Constant{RetType: types.NewFieldType(mysql.TypeNull)})
		}
		return true
	}

	sysVar, ok := variable.SysVars[name]
	if !ok {
		// select null sys vars is not permitted
		er.err = variable.UnknownSystemVar.Gen("Unknown system variable '%s'", name)
		return false
	}
	if sysVar.Scope == variable.ScopeNone {
		er.ctxStack = append(er.ctxStack, datumToConstant(types.NewDatum(sysVar.Value), mysql.TypeString))
		return true
	}

	if v.IsGlobal {
		value, err := globalVars.GetGlobalSysVar(er.b.ctx, name)
		if err != nil {
			er.err = errors.Trace(err)
			return false
		}
		er.ctxStack = append(er.ctxStack, datumToConstant(types.NewDatum(value), mysql.TypeString))
		return true
	}
	d := sessionVars.GetSystemVar(name)
	if d.IsNull() {
		if sysVar.Scope&variable.ScopeGlobal == 0 {
			d.SetString(sysVar.Value)
		} else {
			// Get global system variable and fill it in session.
			globalVal, err := globalVars.GetGlobalSysVar(er.b.ctx, name)
			if err != nil {
				er.err = errors.Trace(err)
				return false
			}
			d.SetString(globalVal)
			err = sessionVars.SetSystemVar(name, d)
			if err != nil {
				er.err = errors.Trace(err)
				return false
			}
		}
	}
	er.ctxStack = append(er.ctxStack, datumToConstant(d, mysql.TypeString))
	return true
}