SQL Server - Include table name programatically - sql

Question

I am in the process of writing a pretty large query that selects from multiple tables and unions them. Because of some really poor database design, a table is created for every user.
What I am doing is something like this:
SELECT *
FROM tbl1
UNION ALL
SELECT *
FROM tbl2
What I am looking for is something generic to add to each line that will enable me to select the table name along with what's inside the table.
I won't accept the below as an answer, because that is not what I've asked for.
SELECT *, 'tbl1'
FROM tbl1
UNION ALL
SELECT *, 'tbl2'
FROM tbl2

Answer 1

To do something like that you either have to make some rather complex and large query into the system views (sys.tables and sys.columns)
But you're properly better off building the query dynamically in what ever code lanuage you use and execute it as a string:
A very rough example could be something like
DECLARE #tableName varchar(255) = 'tbl1';
DECLARE #tableName2 varchar(255) = 'tbl2';
DECLARE #columnList varchar(255) = 'Col1, Col2, Col3';
EXEC(
'SELECT '+ #columnList +' FROM ' +#tableName + '
UNION ALL
SELECT '+ #columnList +' FROM ' +#tableName2
);

Answer 2

Before each select from the table add a SELECT NULL, NULL, 'tableName'; (add as many NULL as table columns so that union all doesn't 'fail'. Or Instead of NULL use '-' or whatever.
I guess the tables looping and obtaining the column names shouldn't be an issue..
Below demo:
create table #t1(C1 int, C2 int)
create table #t2(C1 int, C2 int)
insert #t1 (C1, C2) values (1,2)
insert #t2 (C1, C2) values (3,4)
insert #t2 (C1, C2) values (5,6)
declare #t1 varchar(10) = '#t1';
declare #t2 varchar(10) = '#t2';
declare #cols varchar(100) = 'C1, C2';
declare #sql nvarchar(4000) = ''
set #sql =
' SELECT NULL, NULL, ''' + #t1 + ''' ' + char(10) + char(13) +
' UNION ALL ' + char(10) + char(13) +
' SELECT '+ #cols +', NULL FROM ' + #t1 + char(10) + char(13) +
' UNION ALL ' + char(10) + char(13) +
' SELECT NULL, NULL, ''' + #t2 + ''' ' + char(10) + char(13) +
' UNION ALL ' + char(10) + char(13) +
' SELECT '+ #cols +', NULL FROM ' + #t2
-- select #sql
exec (#sql);

Answer 3

In production code you already need to construct a query that has FROM table_name so you should just add that table name in as a projected column at the same time.
Technically there is a way of doing this in versions that support dm_db_page_info though but this would be very inefficient and require elevated permissions.
CREATE TABLE dbo.T(X INT);
INSERT INTO T VALUES (1),(2),(3);
SELECT OBJECT_NAME(pg_info.object_id) AS table_name, T.*
FROM dbo.T
CROSS APPLY sys.fn_PhysLocCracker(%%physloc%%) pl
CROSS APPLY sys.dm_db_page_info(db_id(), pl.file_id, pl.page_id, 'LIMITED') pg_info
Returns
+------------+---+
| table_name | X |
+------------+---+
| T | 1 |
| T | 2 |
| T | 3 |
+------------+---+