SELECT data from multiple tables using max? - sql

Question

I have Project and Score tables like this
How do I query to get this result, to show all ProjectID, ProjectName, and its newest Score (latest Date) with the Date:
I tried:
SELECT R.ProjectID, Name, Score, Date
FROM PWINProject, PWINRecord R
WHERE Date = (
SELECT max(Date)
FROM PWINRecord
WHERE ProjectID = R.ProjectID
)
AND PWINProject.ProjectID = R.ProjectID
But it only shows me projects with a score, when a project doesn't have a score yet (e.g. #3 - Amazon) it won't show.

Answer 1

You need a left join instead on an inner join (and use a proper join not the non-standard old style join you are using). However it also simplifies the query to use a window function to determine what row to return e.g.
declare #PWINProject table (ProjectId int, [Name] varchar(256))
insert into #PWINProject(ProjectId, [Name])
select 1, 'Database'
union all select 2, 'Microsoft'
union all select 3, 'Amazon'
union all select 4, 'IBM'
declare #PWINRecord table (ScoreId int, ProjectId int, Score int, [Date] datetime)
insert into #PWINRecord (ScoreId, ProjectId, Score, [Date])
select 1, 1, 100, '2019-01-15 19:40:46.723'
union all select 2, 1, 52, '2019-01-15 20:40:46.723'
union all select 3, 2, 60, '2019-01-15 21:40:46.723'
union all select 4, 2, 55, '2019-01-15 22:40:46.723'
union all select 5, 2, 72, '2019-01-15 23:41:46.723'
union all select 6, 4, 111, '2019-01-16 10:40:46.723'
union all select 7, 4, 90, '2019-01-17 12:40:46.723'
select ProjectId, [Name], Score, [Date]
from (
SELECT P.ProjectID, [Name], Score, [Date]
, row_number() over (partition by R.ProjectID order by [Date] desc) Row#
FROM #PWINProject P
left join #PWINRecord R on R.ProjectID = P.ProjectID
) X
where X.Row# = 1
order by ProjectId
Returns:
ProjectID Name Score Date
1 Database 52 2019-01-15 20:40:46.723
2 Microsoft 72 2019-01-15 23:41:46.723
3 Amazon NULL NULL
4 IBM 90 2019-01-17 12:40:46.723
PS: This is the recommended style for posting an SQL question, where you setup the data into temp tables or table variables yourself - saves people answering a lot of time. Data in images is a no-no.

Answer 2

One approach would be to use OUTER APPLY:
DECLARE #Project TABLE (ProjectId INT, ProjectName VARCHAR(100))
INSERT INTO #Project
VALUES (1, 'Database'), (2, 'Microsoft'), (3, 'Amazon'), (4, 'IBM')
DECLARE #Score TABLE(ScoreId INT, ProjectId INT, Score INT, RefDate DATE)
INSERT INTO #Score
VALUES (1, 1, 100, '2019-01-01'), (2, 2, 200, '2019-02-02'), (4, 4, 400, '2019-04-04')
SELECT
P.ProjectId,
P.ProjectName,
S.Score,
S.RefDate
FROM #Project P
OUTER APPLY (
SELECT TOP 1 S.*
FROM #Score S
WHERE S.ProjectId = P.ProjectId ORDER BY S.RefDate DESC
) S
You need to be careful outer apply is not very efficient but it's clean and easy to understand. Other techniques may work involving ROW_NUMBER, you should study a bit the execution plan to see what fits best.

Answer 3

Try this:
select P.ProjectID, P.ProjectName, R.Score, R.Date
from PWINProject P
left outer join PWINRecord R on R.ProjectID = P.ProjectID
and R.Date = (
select max(R2.Date)
from PWINRecord R2
where R2.ProjectID = R.ProjectID
)

Answer 4

A simple solution is the following:
select p.ProjectID, p.ProjectName, s.Score as LatestScore, s.[date]
from Project as p
left outer join Scores as s ON p.ProjectID = s.ProjectID
where (
s.[date] = (
select top (1) s2.[date]
from Scores as s2
where s2.ProjectID = s.ProjectID
order by [date] desc
)
or s.[date] is null
)

Answer 5

CREATE TABLE [dbo].[PWINProject](
[ProjectID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NULL,
CONSTRAINT [PK_PWINProject] PRIMARY KEY CLUSTERED
(
[ProjectID] ASC
) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
CREATE TABLE [dbo].[PWINRecord](
[ScoreId] [int] NOT NULL,
[ProjectID] [int] NULL,
[Score] [int] NULL,
[Date] [datetime] NULL,
CONSTRAINT [PK_PWINRecord] PRIMARY KEY CLUSTERED
(
[ScoreId] ASC
) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
SET IDENTITY_INSERT [dbo].[PWINProject] ON
INSERT [dbo].[PWINProject] ([ProjectID], [Name]) VALUES (1, N'Database')
INSERT [dbo].[PWINProject] ([ProjectID], [Name]) VALUES (2, N'Microsoft')
INSERT [dbo].[PWINProject] ([ProjectID], [Name]) VALUES (3, N'Amazone')
INSERT [dbo].[PWINProject] ([ProjectID], [Name]) VALUES (4, N'IBM')
SET IDENTITY_INSERT [dbo].[PWINProject] OFF
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (1, 1, 100, CAST(N'2019-01-15 00:00:00.000' AS DateTime))
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (2, 1, 52, CAST(N'2019-01-15 00:00:00.000' AS DateTime))
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (3, 2, 60, CAST(N'2019-01-15 00:00:00.000' AS DateTime))
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (4, 2, 55, CAST(N'2019-01-15 00:00:00.000' AS DateTime))
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (5, 2, 72, CAST(N'2019-01-15 00:00:00.000' AS DateTime))
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (6, 4, 111, CAST(N'2019-01-16 00:00:00.000' AS DateTime))
INSERT [dbo].[PWINRecord] ([ScoreId], [ProjectID], [Score], [Date]) VALUES (7, 4, 90, CAST(N'2019-01-17 00:00:00.000' AS DateTime))
ALTER TABLE [dbo].[PWINRecord] WITH CHECK ADD CONSTRAINT [FK_PWINRecord_PWINProject] FOREIGN KEY([ProjectID])
REFERENCES [dbo].[PWINProject] ([ProjectID])
ALTER TABLE [dbo].[PWINRecord] CHECK CONSTRAINT [FK_PWINRecord_PWINProject]
-- To select your desired output run the below code
;WITH CTE
AS
(
SELECT p.ProjectID, p.Name, r.Score, r.[Date], ROW_NUMBER()OVER (PARTITION BY R.ProjectID ORDER BY r.[Date] DESC) RN
FROM PWINProject p
full join PWINRecord R on p.ProjectID =r.ProjectID
)
SELECT ProjectID, Name, Score, [Date]
FROM CTE
WHERE RN = 1