Select from a loop to a list of table that has similar name but with increment numbers added - sql

Question

I would like to use a query to loop through tables that are similar in names but added a number after that (ie. tableJan01, tableJan02, tableJan03, etc..., tableJan30)
Is there a way in SQL Server to use the same query statement while varying the table name within it. (similar to using parameter values) (need this to add different input to each different month's table)
declare #x nvarchar(50) ='abc'
declare #z int =1
while (#z<30)
BEGIN
SET #z = #z + 1;
select * from (#x)
END;
this shows error
Must declare the scalar variable "#CharVariable".
this script shows too syntax error
declare #x nvarchar(50) ='abc'
declare #z int =1
while (#z<30)
BEGIN
SET #z = #z + 1;
select * from (#x+#z)
END;
also, simple code like this doesn't work too
declare #x nvarchar(50) ='abc'
select * from #x

Answer 1

I agree with John Cappelletti that this requirement feels like a design flaw, however, to get your list of table names you can do something like this:
declare #x nvarchar(50) ='abc'
declare #z int =1
declare #ListOfTableNames TABLE (TableName nvarchar(50));
while (#z<30)
BEGIN
SET #z = #z + 1;
INSERT INTO #ListOfTableNames (TableName) VALUES (#x + CONVERT(NVARCHAR(20), #z))
END
SELECT * FROM #ListOfTableNames
To do dynamic SQL on these tables you could build a query string and then pass that string to the sp_executesql proc. You could put that logic in place of the line where we populate the table variable with the numbered table names. Like this:
declare #x nvarchar(50) ='abc'
declare #z int =1
declare #sql NVARCHAR(100)
while (#z<30)
BEGIN
SET #z = #z + 1;
SET #sql ='SELECT * FROM '+ (#x + CONVERT(NVARCHAR(20), #z))
EXEC sp_executesql #sql
END

Answer 2

I would completely avoid a WHILE loop just use some pattern matching:
DECLARE #Prefix sysname = N'abc';
DECLARE #SQL nvarchar(MAX),
#CRLF nchar(2) = NCHAR(13) + NCHAR(10);
SET #SQL = STUFF((SELECT #CRLF +
N'SELECT *' + #CRLF +
--N' ,N' + QUOTENAME(t.[name],'''') + N' AS TableName' + #CRLF + --Uncomment if wanted
N'FROM ' + QUOTENAME(s.[name]) + N'.' + QUOTENAME(t.[name]) + N';'
FROM sys.schemas s
JOIN sys.tables t ON s.schema_id = t.schema_id
WHERE t.[name] LIKE #Prefix + '%'
AND t.[name] NOT LIKE #Prefix + N'%[^0-9]'
ORDER BY t.[name]
FOR XML PATH(N''),TYPE).value('.','nvarchar(MAX)'),1,2,N'');
--PRINT #SQL;
EXEC sp_executesql #SQL;
DB<>Fiddle
But John is right, you certainly have a design flaw here.

Answer 3

Using dynamic SQL, it would look something like this:
declare
#Base_table_name nvarchar(50) = 'my_table'
,#Step int = 1
,#SQL nvarchar(max);
while(#Step < 30)
begin
set #SQL = 'select * from ' + #Base_table_name + right('00' + cast(#Step as nvarchar(50)),2);
print(#SQL); --this displays the SQL that would be run
--exec(#SQL) --uncomment this to run the dynamic SQL
set #Step+=1;
end;
Alternatively, you can be more precise by using the sys.schemas and sys.tables tables like so:
declare
#Base_table_name sysname = 'my_table'
,#schema_name sysname = 'my_schema'
,#Step int = 1
,#StepCount int = 0
,#SQL nvarchar(max);
/* This will create a table variable and populate it with all the tables you'll want to query */
declare #tables_to_query table (Step int identity, SchemaName sysname, TableName sysname);
insert into #tables_to_query(SchemaName, TableName)
select
s.name
,t.name
from
sys.schemas s
inner join
sys.tables t on s.schema_id = t.schema_id
where
s.name = #schema_name --this will limit the tables to this schema
and t.name like #Base_table_name + '%' --this will look for any table that starts with the base table name
/* this loops through all the tables in the table variable */
while(#Step <= #StepCount)
begin
select
#SQL = 'select * from ' + quotename(SchemaName) + '.' + quotename(TableName)
from
#tables_to_query
where
Step = #Step
print(#SQL); --this displays the SQL that would be run
--exec(#SQL) --uncomment this to run the dynamic SQL
set #Step+=1;
end;

Answer 4

The dynamic SQL approaches laid out in other answers will certainly get the job done for you, but if you find you're querying all of these tables frequently, it might server you well to build out a VIEW and query that as needed.
In keeping with Larnu's suggestion of putting the source table name into the result set, I'd probably do something like this:
CREATE VIEW dbo.vwJan
AS
SELECT
'tableJan01' AS SourceTable,
<Column List>
FROM dbo.tableJan01
UNION ALL
...<28 other iterations>
SELECT
'tableJan30' AS SourceTable,
<Column List>
FROM dbo.tableJan30;
From there, you can go ahead and query them all to your heart's content with a single statement.
SELECT
SourceTable,
<Any other columns you're interested in>
FROM
vwJan;