Looping through different tables of different dates - sql

Question

We have a legacy application which created multiple tables with the following naming convention: table_20140618, table_20140623, etc where the date is when the program run. I am trying to clean up the database now, and drop some of these tables.
In each table there are two fields: DateStarted and DateFinished. I want to select the tables (and then drop them) where DateStarted has value and DateFinished is NOT null.
At the moment I am using the following query to select all the tables that start with 'table_'
such as:
Select (TABLE_NAME) FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_TYPE = 'BASE TABLE'
AND TABLE_NAME LIKE 'table_%';
I am not sure how to get all the tables together by searching within their fields. I could do it through the code, but that should mean multiple hits on the database. Any ideas?

Answer 1

Made this after my first comment above, but you should be able to alter the code to fit your specs. Basically, this will use dynamic SQL to generate the commands based on your filters and conditions. So you can use whatever conditions you want in the SELECT #SQL = ... part, to check for the dates, and then add the table name when the conditions are met.
The script returns a list with tablenames and the drop command, so you can check what you're doing before you do it. But from there you can just copy the drop command list and execute it if you want.
IF OBJECT_ID('tempdb..#TABLES') IS NOT NULL
DROP TABLE #TABLES
CREATE TABLE #TABLES (ROWNMBER INT IDENTITY(1,1), TABLENAME VARCHAR(256) COLLATE DATABASE_DEFAULT)
/*
-- Old code to fetch ALL tables with specified name
INSERT INTO #TABLES
SELECT name
FROM sys.tables
WHERE name LIKE 'table[_]%'
*/
-- Updated code to fetch only those tables which contain the DateStarted and DateFinished columns
INSERT INTO #TABLES
SELECT TAB.name
FROM sys.tables TAB
LEFT JOIN sys.columns C1 on C1.object_id = TAB.object_id
AND C1.name = 'DateStarted'
LEFT JOIN sys.columns C2 on C2.object_id = TAB.object_id
AND C2.name = 'DateFinished'
WHERE TAB.name LIKE 'table[_]%'
AND C1.name IS NOT NULL AND C2.name IS NOT NULL
IF OBJECT_ID('tempdb..#DROPPABLE_TABLES') IS NOT NULL
DROP TABLE #DROPPABLE_TABLES
CREATE TABLE #DROPPABLE_TABLES (TABLENAME VARCHAR(256) COLLATE DATABASE_DEFAULT)
DECLARE #ROW_NOW INT, #ROW_MAX INT, #SQL VARCHAR(MAX), #TABLENAME VARCHAR(256)
SELECT #ROW_NOW = MIN(ROWNMBER), #ROW_MAX = MAX(ROWNMBER) FROM #TABLES
WHILE #ROW_NOW <= #ROW_MAX
BEGIN
SELECT #TABLENAME = TABLENAME FROM #TABLES WHERE ROWNMBER = #ROW_NOW
SELECT #SQL =
'IF (SELECT COUNT(*) FROM '+#TABLENAME+' WHERE DateStarted IS NOT NULL) > 0
AND (SELECT COUNT(*) FROM '+#TABLENAME+' WHERE DateFinished IS NOT NULL) > 0
SELECT '''+#TABLENAME+''''
INSERT INTO #DROPPABLE_TABLES
EXEC(#SQL)
SET #ROW_NOW = #ROW_NOW+1
END
SELECT *, 'DROP TABLE '+TABLENAME DROPCOMMAND FROM #DROPPABLE_TABLES
EDIT:
As per your comment, it seems not all such tables have those columns. You can use the following script to identify said tables and which column is missing, so you can check into them further. And you can use the same idea to filter the results of the first query to only count in tables which have those columns.
SELECT TAB.name TABLENAME
, CASE WHEN C1.name IS NULL THEN 'Missing' ELSE '' END DateStarted_COL
, CASE WHEN C2.name IS NULL THEN 'Missing' ELSE '' END DateFinished_COL
FROM sys.tables TAB
LEFT JOIN sys.columns C1 on C1.object_id = TAB.object_id
AND C1.name = 'DateStarted'
LEFT JOIN sys.columns C2 on C2.object_id = TAB.object_id
AND C2.name = 'DateFinished'
WHERE TAB.name LIKE 'table[_]%'
AND (C1.name IS NULL
OR C2.name IS NULL)