一、SELECT
1.连接
操作符:||
select name || 'is a ' || job as "studentdesc" from student
结果是:
___________
| studentdesc |
———————
|小明 is a stu |
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2.去重复行
关键字:distinct
select distinct classid from student
如果不加distinct关键字,去学生表里查班级可能查出好多重复的班级id
3.别名
别名的三种写法:
select name as Name from student; --> 显示的是NAME
select name Name from student; --> 显示的是NAME
select name "Name" from student; --> 显示的是Name(双引号中的内容大小写敏感了)