Passing data into nested cursors in TSQL - sql

Question

I have a cursor that gets data and fetches it into #data_table. Then in the while loop I want to pass that #data_table into another cursor (as the table name) to run some more processing. I keep getting a declare #data_table error. How do I fix this?
DECLARE #var_name varchar(50)
DECLARE #data_table varchar(50)
DECLARE #data_value varchar(50)
DECLARE curDiscreteVars CURSOR LOCAL
FOR SELECT DISTINCT v.var_name, v.data_table
FROM dbo.vars v
GROUP BY v.var_name, v.data_table
-- Loop through cursor, translating variable values as needed, and generate counts for each val_code for a variable
OPEN curDiscreteVars
FETCH NEXT FROM curDiscreteVars
INTO #var_name, #data_table
WHILE ##FETCH_STATUS = 0
BEGIN
--loop through all possible data values
DECLARE curValues CURSOR LOCAL
FOR SELECT DISTINCT #var_name
FROM #data_table
OPEN curValues
FETCH NEXT FROM curValues
INTO #data_value
WHILE ##FETCH_STATUS = 0
BEGIN
print #var_name
FETCH NEXT FROM curValues
INTO #data_value
END
CLOSE curValues
DEALLOCATE curValues
FETCH NEXT FROM curDiscreteVars
INTO #var_name, #data_table
END
CLOSE curDiscreteVars
DEALLOCATE curDiscreteVars

Answer 1

For my part, i don't like cursors! For me cursors are evil. The give you locks and such that you don't want.
What i always do is create a temp table with the values (like you normally insert into the cursor) and loop through it with a while loop
like this :
declare #currow int
, #totrow int
create table #tmp_values (id int identity(1, 1), val int)
insert
into #tmp_values
select val
from tableX
set #totrow = ##rowcount
set #currow = 1
while #totrow > 0 and #currow <= #totrow
begin
select #val = val
from #tmp_values
where id = #currow
set #currow = #currow + 1
end
That way you have more control of things and you can re-use the tmp table

Answer 2

I'm not sure I understand what you're talking about doing, but variables cannot be used as table names. Or, really anything that's not a field name. You'll need to use dynamic SQL. That is, assign your SQL string to a variable, an then run EXEC() command.
For example:
DECLARE #sqlcmd varchar(max)
DECLARE #table_name sysname
DECLARE cur_tables FOR
SELECT name FROM sys.tables
OPEN cur_tables
FETCH NEXT FROM cur_tables INTO #table_name
WHILE ##FETCH_STATUS = 0 BEGIN
SET #sqlcmd = 'SELECT TOP 10 * FROM ' + QUOTENAME(#table_name)
EXEC ( #sqlcmd )
FETCH NEXT from cur_tables INTO #table_name
END
CLOSE cur_tables
DEALLOCATE cur_tables
Alternately, if what you mean is that you need a location to store the data that is like a table, then create a temporary tabled for it.