Dynamic sql script to generate list of drop table statement - sql

Question

I've list of tables (around 100++) that need to be dropped from SQL Server. Below is the sample code that I would use
IF OBJECT_ID('dbo.DS_Area_TBL', 'U') IS NOT NULL
drop table dbo.DS_Area_TBL
Print 'dbo.DS_Area_TBL has been dropped'
I need to replace table name 100++ time with other table name. How to write a dynamic sql script that can auto generate list of queries?

Answer 1

DECLARE #SQL NVARCHAR(MAX)
SELECT #SQL = (
SELECT '
IF OBJECT_ID(''' + obj + ''', ''U'') IS NOT NULL BEGIN
DROP TABLE ' + obj + '
PRINT ''' + obj + ' has been dropped''
END
'
FROM (
SELECT obj = QUOTENAME(s.name) + '.' + QUOTENAME(o.name)
FROM sys.objects o
JOIN sys.schemas s ON o.[schema_id] = s.[schema_id]
WHERE o.[type] = 'U'
--AND o.name LIKE 'table%'
--AND s.name IN ('dbo')
) t
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)')
PRINT #SQL
--EXEC sys.sp_executesql #SQL
Output -
IF OBJECT_ID('[dbo].[user_data]', 'U') IS NOT NULL BEGIN
DROP TABLE [dbo].[user_data]
PRINT '[dbo].[user_data] has been dropped'
END
IF OBJECT_ID('[dbo].[formatter_options]', 'U') IS NOT NULL BEGIN
DROP TABLE [dbo].[formatter_options]
PRINT '[dbo].[formatter_options] has been dropped'
END

Answer 2

You could first generate script then execute with dynamic sql:
CREATE TABLE a(a INT);
CREATE TABLE b(a INT);
CREATE TABLE c(a INT);
CREATE TABLE d(a INT);
CREATE TABLE e(a INT);
CREATE TABLE tab(tab_name SYSNAME); -- here are table names stored
INSERT INTO tab VALUES ('a'),('b'),('c'),('d'),('e');
-- main part
DECLARE #sql NVARCHAR(MAX);
SELECT #sql = STUFF((SELECT ' ' + FORMATMESSAGE(
'IF OBJECT_ID(''%s'', ''U'') IS NOT NULL
BEGIN
DROP TABLE %s;
PRINT ''%s has been dropped '';
END
', QUOTENAME(tab_name),QUOTENAME(tab_name),QUOTENAME(tab_name))
FROM tab
FOR XML PATH('')), 1, 1, '');
PRINT #sql; -- for debug
EXEC [dbo].[sp_executesql]
#sql;
If you use version of SQL Server lower than 2012 you need to change FORMATMESSAGE with string concatenation +.
You could easily extend this script with custom schema and so on by modifying template:
'IF OBJECT_ID(''%s'', ''U'') IS NOT NULL
BEGIN
DROP TABLE %s;
PRINT ''%s has been dropped '';
END
'
Output:
IF OBJECT_ID('[a]', 'U') IS NOT NULL
BEGIN
DROP TABLE [a];
PRINT '[a] has been dropped ';
END
IF OBJECT_ID('[b]', 'U') IS NOT NULL
BEGIN
DROP TABLE [b];
PRINT '[b] has been dropped ';
END
IF OBJECT_ID('[c]', 'U') IS NOT NULL
BEGIN
DROP TABLE [c];
PRINT '[c] has been dropped ';
END
IF OBJECT_ID('[d]', 'U') IS NOT NULL
BEGIN
DROP TABLE [d];
PRINT '[d] has been dropped ';
END
IF OBJECT_ID('[e]', 'U') IS NOT NULL
BEGIN
DROP TABLE [e];
PRINT '[e] has been dropped ';
END
EDIT:
How it works:
XML + STUFF for string concatenation is common idiom with SQL Server, works like GROUP_CONCAT in MySQL. You can think about it as a way to combine multiple IF BEGIN END chunks into one string.
FORMATMESSAGE will replace %s with actual table names(quoted to avoid SQL Injection attacks)
PRINT is for debug to check generated query, can be commented
sp_executesql will execute SQL string