SQL 数据库的若干问题

1、select from tb_reader tr where trlength>3; 这里面偷懒，用代替了字段，需要哪些字段，自己添加吧

2、select trreaderid,trreadername,sum(tbbookid) from tb_reader tr join tb_bookdet tb on tbbookcode = trbookcode group by trreaderid,trreadername ;

3、select trreadername from tb_reader tr where exists (select 1 from tb_bookdet tb where trtbbookcode = trbookcode and tbstatus ='借出');

4、create view view_bookinfo as select tbibookid, tbibookname, tbiauthor, tbipublisher from tb_reader tr

join tb_bookdet tb on tbbookcode = trbookcode

join tb_bookinfo tbi on tbbookid = tbibookid

where trbackdate > sysdate and trbackdate - sysdate <10;

5、create nonclustered index INDEX_DEPARTMENT tb_reader(department);---创建索引，department该字段非空、且不重复。

alter table tb_reader add primary key nonclustered(department); ----修改索引

select into dept1 from department 的意思是复制表department的结构和内容，把结构和内容存到新表dept1，要这样 *** 作需要数据库里面没有表dept1，你要导入dept1的结构和内容到department，语句：

select into department from dept1

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