我有两个以下查询:SQL子查询或INNER-JOIN?
declare @UserId as int
set @UserId = 1
-- Query #1: Sub-query
SELECT
u.[Id] ,
u.[Name] ,
u.[OrgId] AS Organization,
(SELECT o.[Name] FROM Org o WHERE o.Id = u.OrgId) As OrganizationName,
[UserRoleId] AS UserRole,
[UserCode] AS UserCode,
[EmailAddress] As EmailAddress,
(SELECT SearchExpression FROM SearchCriteria WHERE UserId = @UserId AND IsDefault=1) AS SearchCriteria,
(SELECT PageSize FROM UserPreferences WHERE UserId = @UserId) AS UserPreferencePageSize,
(SELECT DrilldownPageSize FROM UserPreferences WHERE UserId = @UserId) AS UserPreferenceDrilldownPageSize
FROM [User] as u
WHERE u.Id = @UserId
-- Query #2: LEFT OUTER JOIN-query
SELECT
u.[Id] ,
u.[Name] ,
u.[OrgId] AS Organization,
(SELECT o.[Name] FROM Org o WHERE o.Id = u.OrgId) As OrganizationName,
[UserRoleId] AS UserRole,
[UserCode] AS UserCode,
[EmailAddress] As EmailAddress,
sc.SearchExpression As SearchExpression,
up.PageSize As PageSize,
up.DrilldownPageSize As DrilldownPageSize
FROM [User] as u
LEFT OUTER JOIN [UserPreferences] as up ON u.id = up.UserId
LEFT OUTER JOIN [SearchCriteria] as sc ON u.id = sc.UserId
WHERE ISNULL(sc.IsDefault,1)=1 AND u.Id = @UserId
查询执行计划的统计:(相对于批次查询成本)
- 查询#1(子查询):56%
- 查询#2(加入):44%
我打算子查询将是最优的,因为子查询将在执行后应用WHERE过滤器。统计数据表明查询#2 - JOIN方法更好。
请建议。作为一个适度的SQL服务器用户,我怎样才能得出哪个查询更好(除了执行计划之外的任何其他执行计划,如果它更有帮助)
谢谢。
- 查询#3:完全LEFT OUTER JOIN查询 选择 \t U [ID], \t U [名], \t U [ORGID] AS。组织, \t u.OrgId作为ORGID, O操作。[名]作为单位名称, \tü。[UserRoleId] AS的UserRole, \tü。[USERCODE] AS USERCODE, \tü。[EmailAddress的作为EmailAddress的,\t \t sc.SearchExpression As SearchExpression, \t up.PageSize由于PageSize, \t up。DrilldownPageSize作为DrilldownPageSize \t FROM [用户]为u LEFT OUTER JOIN [使用UserPreferences]至多ON u.id = up.UserId 左外连接[SearchCriteria如SC ON u.id = sc.UserId LEFT OUTER JOIN [ Org] as o ON o.Id = u.OrgId \t WHERE ISNULL(sc.IsDefault,1)= 1 AND u.Id = @UserId – 2009-11-24 08:59:02