截断、删除和删除表有什么区别？什么时候选择哪个？

Question

表的truncate、drop 和delete 有什么区别？什么时候选择哪个？有人能快速比较吗？我已经看到了很多关于此的信息，但还没有在清晰的概述中找到它。我希望这篇文章有助于理解。

我的意思是喜欢在 t-sql 中的这些语句中使用：

truncate table TableX   
drop table TableX
delete table_name

Answer 1

根据@Michal here 的回答和更多搜索，我在下面对以下语句（在 t-sql 中）进行了比较：truncate table TableX、drop table TableX和delete table_name。

                           Truncate           Drop                 Delete
Speed                      [Fast]             Slow                 Slowest
Rolback possibility        No                 No                   [Yes]
Specifiable conditions     No                 No                   [Yes]
Scope                      All records        All record+Headers   Some records/All records
                                              =whole table 
Cascading effects          No*                No*                  [Yes]** 



**For example: in a Table_1 there is a PK, in Table_2 there is a FK that relates with 
the PK of Table_1, other words there is referential integrity. If the PK has `'ON DELETE CASCADE'` 
and `delete Table_1` is ordered, then the data in Table_2 will be deleted too, 
automatically. For more info about ON DELETE CASCADE and ON ALTER CASCADE, see:
https://technet.microsoft.com/en-us/library/ms186973%28v=sql.105%29.aspx. 

Cascading does automatic alterations and deletes of depending objects such as foreign keys (FK), 
views, and triggers. Sometimes very useful, sometimes very dangerous..

*The drop and truncate statements of a Table_1 (with PK and FK in Table_2, as decribed 
in **) can't be executed, because the ssdms prohibits that. To accomplish the truncation 
or dropping of a Table_1: first get rid of the FK in Table_2, by altering the table design, or 
by dropping table2.

查看比较以决定何时使用哪个语句...

作为一个拇指：

If you want to get rid of only records: 当需要条件删除时使用 delete，当所有记录可能被删除时使用 truncate。当您希望能够回滚时，请使用 delete。

If you want to get rid of the whole table，包括标题（带有设置的列），然后选择 drop。

If you want to get rid of values and automatically the related objects（并在表中定义了级联），使用delete。 （PS：在其他方言中，即使表没有设计级联，似乎也有办法实现它，但据我所知，t-sql/msss 中没有；但如果我错了，请纠正我）

PS：如果你想alter or deletepreferences of a column，那么使用（在t-sql方言中）：

改变：

alter table tableX
alter columnX datatypeX

删除：

alter table tableX
drop column columnX

---

--And here's some code to play with
--table to truncate, drop or delete

create table TableX(
       [Name] [nchar](25) null,
       [ID_Number] [int] not null)


--tables with PK and FK 
create table Table_1(
       [Name] [nchar](25) null,
       [ID_Number] [int] not null primary key)

create table Table_2(
       [ID_Number] int not null foreign key references Table_1(ID_Number) on delete cascade,
       [Buys] [int] null)

--the on delete cascade make it happen that when a ID_Number is Table_1 is deleted, that row
is automatically deleted in Table_2 too. But not the other way around, 
therefor alter the design of Table_1.

insert into Table_1 (Name,ID_Number) values ('A',1),('B',2),('C',3);
insert into Table_2 (ID_Number,Buys) values (1,10),(2,20),(3,30);

select * from Table_1
select * from Table_2

truncate table table_2
truncate table table_1

drop table table_2
drop table table_1

delete Table_1

delete from dbo.table_1 where name='A'   
delete from Table_1 where name like '%'  
delete from dbo.table_2 where ID_Number=2