對于 SQL Server 來說 @ 用于標示變量名字。

例如：

1>

2>

3> DECLARE

3 @testvalue AS VARCHAR(20);

5> BEGIN

3 SET @testvalue = ‘First Test!’;

3 PRINT( @testvalue );

8> END;

9> go

First Test!

對于 Oracle ， @ 可能是標示 鏈接數(shù)據(jù)庫

例如：

SQL> CREATE DATABASE LINK mydblink

2 CONNECT TO test IDENTIFIED BY test123

3 USING '(DESCRIPTION =

4 (ADDRESS_LIST =

5 (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.210)(PORT = 1521)))

6 (CONNECT_DATA = (SERVICE_NAME = orcl)

7 )

8 )';

Database link created.

SQL> select count(1) from user_tables@mydblink;

COUNT(1)

----------

6