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Oracle笔记:数据操作

Jun 07, 2016 pm 05:11 PM
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Oracle笔记:数据操作,在进行数据操作之前,首先需要有几张完整的表。建立两张表,分别为tableA和tableB

在进行数据操作之前,首先需要有几张完整的表。建立两张表,分别为tableA和tableB

create table tableA(id integer,name varchar(25),age number);
insert into tableA values('101','Jack','25');
insert into tableA values('102','mike','22');
insert into tableA values('103','amy','23');

create table tableB(id integer,class number,grade number);
insert into tableB values('101','3','1');
insert into tableB values('104','4','2');
insert into tableB values('105','3','2');

结果如下:

clip_image002


1、 查询空字段

首先在tableA加一条ID为空的记录,如下图所示

clip_image004


查询空字段(null)
select * from 表名 where 字段名 is null;
select * from tableA where id is null;

clip_image006

如上图所示,ID为空的那条记录被查询出来了。

2、ORDER BY 语句
ORDER BY 语句用于根据指定的列对结果集进行排序。
ORDER BY 语句默认按照升序对记录进行排序。
如果希望按照降序对记录进行排序,可以使用 DESC 关键字。
如果希望按照升序对记录进行排序,可以使用 ASC 关键字。
select * from 表名 order by 字段名 DESC/ASC;
select * from tableA order by age desc;
select * from tableA order by age asc;

clip_image008

 

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