TSQL -- quick way to get a count across all tables - tsql

Question

If database d1 has tables T1,T2,T3,T4 all with the field "Date1".
What is the best way to get a count of all records across all tables with a date older than 3 days ago?
I know one could do unions, I assume there is no nifty syntax that would omit all tables [like a 'parent' object in C++].
Here best may mean more efficient, or just a pleasing syntax in T-SQL.
This is for SSMS 17.7. Microsoft SQL Server 2014 (SP2)

Answer 1

If you know the table names in advance, a simple query on union all will probably be the simplest way:
SELECT COUNT(*)
FROM
(
SELECT Date1
FROM T1
UNION ALL
SELECT Date1
FROM T2
SELECT Date1
FROM T3
SELECT Date1
FROM T4
) As t
WHERE Date1 <= DATEADD(DAY, -3, GETDATE())
If you don't know the table names in advance, you can use information_schema.columns to build the union query dynamically.

Answer 2

Well, you're interested in a parent object, that would be a view, then. You can reuse it for a variety of queries. Alternatively, add more columns if you need them:
CREATE VIEW parent AS
SELECT Date1 FROM t1 UNION ALL
SELECT Date1 FROM t2 UNION ALL
SELECT Date1 FROM t3 UNION ALL
SELECT Date1 FROM t4;
And now, that can be queried in the way you want
SELECT COUNT(*) FROM parent WHERE Date1 <= DATEADD(DAY, -3, GETDATE())

Answer 3

Without UNION?
Since a COUNT without a GROUP BY returns 1 value, why not use CROSS JOIN for once?
SELECT
t1.Cnt AS [T1],
t2.Cnt AS [T2],
t3.Cnt AS [T3],
t4.Cnt AS [T4],
(t1.Cnt + t2.Cnt + t3.Cnt + t4.Cnt) AS [T1234]
FROM
(SELECT COUNT(*) AS Cnt FROM T1 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t1
CROSS JOIN
(SELECT COUNT(*) AS Cnt FROM T2 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t2
CROSS JOIN
(SELECT COUNT(*) AS Cnt FROM T3 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t3
CROSS JOIN
(SELECT COUNT(*) AS Cnt FROM T4 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t4
Or a CROSS APPLY
SELECT
t1.Cnt AS [T1],
t2.Cnt AS [T2],
t3.Cnt AS [T3],
t4.Cnt AS [T4],
(t1.Cnt + t2.Cnt + t3.Cnt + t4.Cnt) AS [T1234]
FROM (SELECT CAST(GetDate()-3 AS DATE) as Dt) d
CROSS APPLY (SELECT COUNT(*) AS Cnt FROM T1 WHERE [Date1] < d.Dt) AS t1
CROSS APPLY (SELECT COUNT(*) AS Cnt FROM T2 WHERE [Date1] < d.Dt) AS t2
CROSS APPLY (SELECT COUNT(*) AS Cnt FROM T3 WHERE [Date1] < d.Dt) AS t3
CROSS APPLY (SELECT COUNT(*) AS Cnt FROM T4 WHERE [Date1] < d.Dt) AS t4
Example snippet for Sql Server:
declare #T1 table (id int primary key identity(1,1), [Date1] date);
declare #T2 table (id int primary key identity(1,1), [Date1] date);
declare #T3 table (id int primary key identity(1,1), [Date1] date);
declare #T4 table (id int primary key identity(1,1), [Date1] date);
insert into #T1 ([Date1]) values (getdate()-6),(getdate()-5),(getdate()-4),(getdate()-3),(getdate()-2),(getdate()-1),(getdate()-0);
insert into #T2 ([Date1]) select top 6 [Date1] from #T1 order by [Date1] desc;
insert into #T3 ([Date1]) select top 5 [Date1] from #T1 order by [Date1] desc;
insert into #T4 ([Date1]) select top 4 [Date1] from #T1 order by [Date1] desc;
SELECT
t1.Cnt AS [T1],
t2.Cnt AS [T2],
t3.Cnt AS [T3],
t4.Cnt AS [T4],
(t1.Cnt + t2.Cnt + t3.Cnt + t4.Cnt) AS [T1234]
FROM
(SELECT COUNT(*) AS Cnt FROM #T1 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t1
CROSS JOIN
(SELECT COUNT(*) AS Cnt FROM #T2 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t2
CROSS JOIN
(SELECT COUNT(*) AS Cnt FROM #T3 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t3
CROSS JOIN
(SELECT COUNT(*) AS Cnt FROM #T4 WHERE [Date1] < CAST(GetDate()-3 AS DATE)) AS t4
Returns:
T1 T2 T3 T4 T1234
3 2 1 0 6

Answer 4

Instead create a view, you can use a CTE (Common Table Expression). It works like a view, but not persists on database. Please try it:
WITH CteDate( Date1 )
AS ( SELECT Date1 FROM t1 UNION ALL
SELECT Date1 FROM t2 UNION ALL
SELECT Date1 FROM t3 UNION ALL
SELECT Date1 FROM t4
)
SELECT COUNT(*) FROM CteDate WHERE Date1 <= DATEADD(DAY, -3, GETDATE())
It works for all SQL Server greater or equal then 2005.