Retrieve Max loaded date across all tables on a DB - sql

Question

Output I'm trying to get to;
(Database name = ATT)
Table Name
Column name
MAX loaded date = MAX(loaded_date) for this column only
loaded_date is a column in around 50 tables in a database with the same name and datatype (Datetime)
select * FROM sys.tables
select * FROM syscolumns
I've been exploring the system tables without much luck, looking at some posts it may be done dynamic SQL which I've never done.

Answer 1

You can write an sql that writes an sql..
SELECT REPLACE(
'select ''{tn}'' as table_name, max(loaded_date) as ld from {tn} union all'
,'{tn}',table_name)
FROM
information_schema.columns
WHERE
column_name = 'loaded_date'
Run that, then copy all but the final UNION ALL out of the results window and into the query window, and run again
If you wanted to get all this into a single string for dynamic exec, i guess it'd look like (untested) a procedure that contained:
DECLARE #x NVARCHAR(MAX);
SELECT #x =
STRING_AGG(
REPLACE(
'select ''{tn}'' as table_name, max(loaded_date) as ld from {tn}'
,'{tn}',table_name)
,' union all ')
FROM
information_schema.columns
WHERE
column_name = 'loaded_date';
EXECUTE sp_executesql #x;
If your SQLS is old and doesnt have string_agg it's a bit more awkward - but there are many examples of "turn rows into CSV" in sql server that look like STUFF..FOR XML PATH - https://duckduckgo.com/?t=ffab&q=rows+to+CSV+SQLS&ia=web

Answer 2

I wrote up a more permanent type of script that does this. It returns a result set of the list of tables in the current database with a column named loaded_date along with the MAX(loaded_date) result from each table. This script individually queries each table by looping through and running the query on each table individually and keeping track of the max value for each table in a table variable. It also has a #Debug variable that allows you to see the text of the queries that would be run instead of actually running them and implements custom error message to troubleshoot any issues.
/*disable row count messages*/
SET NOCOUNT ON;
/*set to 1 to debug (aka just print queries instead of running)*/
DECLARE #Debug bit = 0;
/*get list of tables to query and assign a unique index to row to assist in looping*/
DECLARE #TableList TABLE(
SchemaAndTableName nvarchar(257) NOT NULL
,OrderToQuery bigint NOT NULL
,MaxLoadedDate datetime NULL
,PRIMARY KEY (OrderToQuery)
);
INSERT INTO #TableList (SchemaAndTableName,OrderToQuery)
SELECT
CONCAT(QUOTENAME(s.name),N'.', QUOTENAME(t.name)) AS SchemaAndTableName
,ROW_NUMBER() OVER(ORDER BY s.name, t.name) AS OrderToQuery
FROM
sys.columns AS c
INNER JOIN sys.tables AS t ON c.object_id = t.object_id
INNER JOIN sys.schemas AS s ON t.schema_id = s.schema_id
WHERE
c.name = N'loaded_date';
/*declare and set some variables for loop*/
DECLARE #NumTables int = (SELECT TOP (1) OrderToQuery FROM #TableList ORDER BY OrderToQuery DESC);
DECLARE #I int = 1;
DECLARE #CurMaxDate datetime;
DECLARE #CurTable nvarchar(257);
DECLARE #CurQuery nvarchar(max);
/*start loop*/
WHILE #I <= #NumTables
BEGIN
/*build text of current query*/
SET #CurTable = (SELECT SchemaAndTableName FROM #TableList WHERE OrderToQuery = #I);
SET #CurQuery = CONCAT(N'SELECT #MaxDateOut = MAX(loaded_date) FROM ', #CurTable, N';');
/*check debugging status*/
IF #Debug = 0
BEGIN
BEGIN TRY
EXEC sys.sp_executesql #stmt = #CurQuery
,#params = N'#MaxDateOut datetime OUTPUT'
,#MaxDateOut = #CurMaxDate OUTPUT;
END TRY
BEGIN CATCH
DECLARE #ErrorMessage nvarchar(max) = CONCAT(
N'Error querying table ', #CurTable, N'.', NCHAR(13), NCHAR(10)
,N'Errored query: ', NCHAR(13), NCHAR(10), #CurQuery, NCHAR(13), NCHAR(10)
,N'Error message: ', ERROR_MESSAGE()
);
RAISERROR(#ErrorMessage,16,1) WITH NOWAIT;
/*on error end loop so error can be investigated*/
SET #I = #NumTables + 1;
END CATCH;
END;
ELSE /*currently debugging*/
BEGIN
PRINT(CONCAT(N'Debug output: ', #CurQuery));
END;
/*update value in our table variable*/
UPDATE #TableList
SET MaxLoadedDate = #CurMaxDate
WHERE
OrderToQuery = #I;
/*increment loop*/
SET #I = #I + 1;
END;
SELECT
SchemaAndTableName AS TableName
,MaxLoadedDate AS Max_Loaded_date
FROM
#TableList;
I like this solution better as querying each table one at a time would be much less system impact than attempting one large UNION ALL query. Querying a large set of a tables all at once could cause some serious resource semaphore or locking contention (depending on usage of your db).
It is fairly well commented, but let me know if something is not clear.
Also, just a note, dynamic SQL should be used as a last resort. I provided this script to answer your question, but you should explore better options than something like this.

Answer 3

You can go for undocumented stored procedure sp_MSforeachtable. But, don't use in production code, as this stored procedure might not be available in future versions.
Read more on sp_MSforeachtable
EXEC sp_MSforeachtable 'SELECT ''?'' as tablename, max(loaded_Date) FROM ?'