完美记忆掌握oracle乘法口诀表（oracle乘法口诀表）

完美记忆：掌握Oracle乘法口诀表

Oracle作为一款强大的数据库管理系统，我们在日常的开发中经常会接触到它。而在实际开发过程中，我们经常需要进行数据的运算，比如乘法。在书写SQL语句时，熟练掌握乘法口诀表可以大大提高我们的工作效率，让我们快速地得出答案。下面，让我们来掌握Oracle乘法口诀表。

1. 使用嵌套循环实现乘法口诀表

在SQL语言中，我们可以使用SELECT语句来实现乘法口诀表。其中，嵌套循环是实现乘法口诀表的重要方式。

代码如下：

SELECT  CONCAT_WS('_',a,b) AS result
FROM    (SELECT @rownum:=@rownum+1 AS rownum
            FROM ANY_OTHER_TABLE t1, (SELECT @rownum:=0) t2
            WHERE @rownum
            JOIN
            (SELECT @rownum1:=@rownum1+1 as a 
            FROM ANY_OTHER_TABLE t1, (SELECT @rownum1:=0) t2
            WHERE @rownum1
            JOIN
            (SELECT @rownum2:=@rownum2+1 as b 
            FROM ANY_OTHER_TABLE t1, (SELECT @rownum2:=0) t2
            WHERE @rownum2
            ON a 
ORDER BY a,result;

在上面的代码中，我们使用了嵌套循环的方式进行了乘法表的实现。其中，我们使用了CONCAT_WS函数来将两个数连接在一起。

2. 使用UNION语句实现乘法口诀表

除了使用嵌套循环的方式实现乘法口诀表之外，我们还可以使用UNION语句来实现。该方法更为简洁，但是需要写多个SELECT语句。

代码如下：

SELECT  CONCAT_WS('_',1,1) AS result
UNION
SELECT  CONCAT_WS('_',1,2) AS result
UNION
SELECT  CONCAT_WS('_',1,3) AS result
UNION
SELECT  CONCAT_WS('_',1,4) AS result
UNION
SELECT  CONCAT_WS('_',1,5) AS result
UNION
SELECT  CONCAT_WS('_',1,6) AS result
UNION
SELECT  CONCAT_WS('_',1,7) AS result
UNION
SELECT  CONCAT_WS('_',1,8) AS result
UNION
SELECT  CONCAT_WS('_',1,9) AS result
UNION
SELECT  CONCAT_WS('_',2,2) AS result
UNION
SELECT  CONCAT_WS('_',2,3) AS result
UNION
SELECT  CONCAT_WS('_',2,4) AS result
UNION
SELECT  CONCAT_WS('_',2,5) AS result
UNION
SELECT  CONCAT_WS('_',2,6) AS result
UNION
SELECT  CONCAT_WS('_',2,7) AS result
UNION
SELECT  CONCAT_WS('_',2,8) AS result
UNION
SELECT  CONCAT_WS('_',2,9) AS result
UNION
SELECT  CONCAT_WS('_',3,3) AS result
UNION
SELECT  CONCAT_WS('_',3,4) AS result
UNION
SELECT  CONCAT_WS('_',3,5) AS result
UNION
SELECT  CONCAT_WS('_',3,6) AS result
UNION
SELECT  CONCAT_WS('_',3,7) AS result
UNION
SELECT  CONCAT_WS('_',3,8) AS result
UNION
SELECT  CONCAT_WS('_',3,9) AS result
UNION
SELECT  CONCAT_WS('_',4,4) AS result
UNION
SELECT  CONCAT_WS('_',4,5) AS result
UNION
SELECT  CONCAT_WS('_',4,6) AS result
UNION
SELECT  CONCAT_WS('_',4,7) AS result
UNION
SELECT  CONCAT_WS('_',4,8) AS result
UNION
SELECT  CONCAT_WS('_',4,9) AS result
UNION
SELECT  CONCAT_WS('_',5,5) AS result
UNION
SELECT  CONCAT_WS('_',5,6) AS result
UNION
SELECT  CONCAT_WS('_',5,7) AS result
UNION
SELECT  CONCAT_WS('_',5,8) AS result
UNION
SELECT  CONCAT_WS('_',5,9) AS result
UNION
SELECT  CONCAT_WS('_',6,6) AS result
UNION
SELECT  CONCAT_WS('_',6,7) AS result
UNION
SELECT  CONCAT_WS('_',6,8) AS result
UNION
SELECT  CONCAT_WS('_',6,9) AS result
UNION
SELECT  CONCAT_WS('_',7,7) AS result
UNION
SELECT  CONCAT_WS('_',7,8) AS result
UNION
SELECT  CONCAT_WS('_',7,9) AS result
UNION
SELECT  CONCAT_WS('_',8,8) AS result
UNION
SELECT  CONCAT_WS('_',8,9) AS result
UNION
SELECT  CONCAT_WS('_',9,9) AS result;

在上面的代码中，我们使用了UNION语句枚举出所有的结果并进行合并。由于每个SELECT语句中只有两个数字，代码显得比较冗长。但是，这种方式可以让我们迅速地得出结果。

结语：

通过上述方法，我们已经学会了如何在Oracle中实现乘法口诀表。在实际开发中，我们可以根据自己的需要进行选择，来提高我们的工作效率。当然，我们还可以使用其他一些方法来实现，比如使用PL/SQL来编写存储过程等等。希望读者可以通过本文学会Oracle乘法口诀表的技巧。