Drop all the tables, stored procedures, triggers, constraints and all the dependencies in one sql statement

To drop all tables:

exec sp_MSforeachtable 'DROP TABLE ?'

This will, of course, drop all constraints, triggers etc., everything but the stored procedures.

For the stored procedures I'm afraid you will need another stored procedure stored in master.

I'd do it in two statements: DROP DATABASE ???

and then CREATE DATABASE ???

You have to disable all triggers and constraints first.

EXEC sp_MSforeachtable @command1="ALTER TABLE ? NOCHECK CONSTRAINT ALL"

EXEC sp_MSforeachtable @command1="ALTER TABLE ? DISABLE TRIGGER ALL"

After that you can generate the scripts for deleting the objects as

SELECT 'Drop Table '+name FROM sys.tables WHERE type='U';

SELECT 'Drop Procedure '+name FROM  sys.procedures WHERE type='P';

Execute the statements generated.

To remove all objects in oracle :

1) Dynamic

DECLARE
CURSOR IX IS
SELECT * FROM ALL_OBJECTS WHERE OBJECT_TYPE ='TABLE' 
AND OWNER='SCHEMA_NAME';
 CURSOR IY IS
 SELECT * FROM ALL_OBJECTS WHERE OBJECT_TYPE 
IN ('SEQUENCE',
'PROCEDURE',
'PACKAGE',
'FUNCTION',
'VIEW') AND  OWNER='SCHEMA_NAME';
 CURSOR IZ IS
 SELECT * FROM ALL_OBJECTS WHERE OBJECT_TYPE IN ('TYPE') AND  OWNER='SCHEMA_NAME';
BEGIN
 FOR X IN IX LOOP
   EXECUTE IMMEDIATE('DROP '||X.OBJECT_TYPE||' '||X.OBJECT_NAME|| ' CASCADE CONSTRAINT');
 END LOOP;
 FOR Y IN IY LOOP
   EXECUTE IMMEDIATE('DROP '||Y.OBJECT_TYPE||' '||Y.OBJECT_NAME);
 END LOOP;
 FOR Z IN IZ LOOP
   EXECUTE IMMEDIATE('DROP '||Z.OBJECT_TYPE||' '||Z.OBJECT_NAME||' FORCE ');
 END LOOP;
END;
/

2)Static

    SELECT 'DROP TABLE "' || TABLE_NAME || '" CASCADE CONSTRAINTS;' FROM user_tables
        union ALL
        select 'drop '||object_type||' '|| object_name || ';' from user_objects 
        where object_type in ('VIEW','PACKAGE','SEQUENCE', 'PROCEDURE', 'FUNCTION')
        union ALL
        SELECT 'drop '
        ||object_type
        ||' '
        || object_name
        || ' force;'
        FROM user_objects
        WHERE object_type IN ('TYPE');

try this with sql2012 or above,

this will help to delete all objects by selected schema

DECLARE @MySchemaName VARCHAR(50)='dbo', @sql VARCHAR(MAX)='';
DECLARE @SchemaName VARCHAR(255), @ObjectName VARCHAR(255), @ObjectType VARCHAR(255), @ObjectDesc VARCHAR(255), @Category INT;

DECLARE cur CURSOR FOR
    SELECT  (s.name)SchemaName, (o.name)ObjectName, (o.type)ObjectType,(o.type_desc)ObjectDesc,(so.category)Category
    FROM    sys.objects o
    INNER JOIN sys.schemas s ON o.schema_id = s.schema_id
    INNER JOIN sysobjects so ON so.name=o.name
    WHERE s.name = @MySchemaName
    AND so.category=0
    AND o.type IN ('P','PC','U','V','FN','IF','TF','FS','FT','PK','TT')

OPEN cur
FETCH NEXT FROM cur INTO @SchemaName,@ObjectName,@ObjectType,@ObjectDesc,@Category

SET @sql='';
WHILE @@FETCH_STATUS = 0 BEGIN    
    IF @ObjectType IN('FN', 'IF', 'TF', 'FS', 'FT') SET @sql=@sql+'Drop Function '+@MySchemaName+'.'+@ObjectName+CHAR(13)
    IF @ObjectType IN('V') SET @sql=@sql+'Drop View '+@MySchemaName+'.'+@ObjectName+CHAR(13)
    IF @ObjectType IN('P') SET @sql=@sql+'Drop Procedure '+@MySchemaName+'.'+@ObjectName+CHAR(13)
    IF @ObjectType IN('U') SET @sql=@sql+'Drop Table '+@MySchemaName+'.'+@ObjectName+CHAR(13)

    --PRINT @ObjectName + ' | ' + @ObjectType
    FETCH NEXT FROM cur INTO @SchemaName,@ObjectName,@ObjectType,@ObjectDesc,@Category
END
CLOSE cur;    
DEALLOCATE cur;
SET @sql=@sql+CASE WHEN LEN(@sql)>0 THEN 'Drop Schema '+@MySchemaName+CHAR(13) ELSE '' END
PRINT @sql
--EXECUTE (@sql)

Seems like a rather dangerous feature to me. If you'd implement something like this I would make sure to properly secure it in a way you won't be able to run this per accident.

As suggested before you could make some sort of stored procedure yourself. In SQL Server 2005 you could have a look this system table to determine and find the objects you would like to drop.

select * from sys.objects

One more sample

declare @objectId int,  @objectName varchar(500), @schemaName varchar(500), @type nvarchar(30), @parentObjId int, @parentObjName nvarchar(500)
declare cur cursor 
for 

select obj.object_id, s.name as schema_name, obj.name, obj.type, parent_object_id
from sys.schemas s
    inner join sys.sysusers u
        on u.uid = s.principal_id
        JOIN
        sys.objects obj on obj.schema_id = s.schema_id
WHERE s.name = 'schema_name' and (type = 'p' or obj.type = 'v' or obj.type = 'u' or obj.type = 'f' or obj.type = 'fn')

order by obj.type

open cur
fetch next from cur into @objectId, @schemaName, @objectName,  @type, @parentObjId
while @@fetch_status = 0
begin
    if @type = 'p'
    begin
        exec('drop procedure ['+@schemaName +'].[' + @objectName + ']')
    end

    if @type = 'fn'
    begin
        exec('drop FUNCTION ['+@schemaName +'].[' + @objectName + ']')
    end

    if @type = 'f'
    begin
        set @parentObjName = (SELECT name from sys.objects WHERE object_id = @parentObjId)
        exec('ALTER TABLE ['+@schemaName +'].[' + @parentObjName + ']' + 'DROP CONSTRAINT ' +  @objectName)
    end

    if @type = 'u'
    begin
        exec('drop table ['+@schemaName +'].[' + @objectName + ']')
    end

    if @type = 'v'
    begin
        exec('drop view ['+@schemaName +'].[' + @objectName + ']')
    end
    fetch next from cur into  @objectId, @schemaName, @objectName,  @type, @parentObjId
end
close cur
deallocate cur

There is no single statement that can be used to achieve this aim.

You could of course create yourself a stored procedure that you could use to perform these various administrative tasks.

You could then execute the procedure using this single statement.

Exec sp_CleanDatabases @DatabaseName='DBname'

Another alternative if you are developing, would be:

DROP SCHEMA public CASCADE;
CREATE SCHEMA public;