MySQL Union合并查询数据及表别名、字段别名用法分析
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2022-03-29 18:41:12
本文实例讲述了mysql union合并查询数据及表别名、字段别名用法。分享给大家供大家参考,具体如下:
union关键字
select s_id, f_nam...
本文实例讲述了mysql union合并查询数据及表别名、字段别名用法。分享给大家供大家参考,具体如下:
union
关键字
select s_id, f_name, f_price from fruits where f_price < 9.0 union all select s_id, f_name, f_price from fruits where s_id in(101,103);
为表取别名
select * from orders as o where o.o_num = 30001;
select c.c_id, o.o_num from customers as c left outer join orders as o on c.c_id = o.c_id;
为字段取别名
select f1.f_name as fruit_name, f1.f_price as fruit_price from fruits as f1 where f1.f_price < 8;
select concat(rtrim(s_name) , ' (', rtrim(s_city), ')') from suppliers order by s_name;
select concat(rtrim(s_name) , ' (', rtrim(s_city), ')') as suppliers_title from suppliers order by s_name;
【例.62】查询所有价格小于9的水果的列表,查询s_id等于101和103所有的水果种类,使用union
连接查询结果
select s_id, f_name, f_price from fruits where f_price < 9.0 union all select s_id, f_name, f_price from fruits where s_id in(101,103);
【例.63】查询所有价格小于9的水果的列表,查询s_id等于101和103所有的水果种类,使用union all
连接查询结果,sql语句如下
select s_id, f_name, f_price from fruits where f_price < 9.0 union all select s_id, f_name, f_price from fruits where s_id in(101,103);
【例.64】为orders表取别名o,查询订30001订单的下单日期
select * from orders as o where o.o_num = 30001;
【例.65】为customers和orders表分别取别名,并进行连接查询
select c.c_id, o.o_num from customers as c left outer join orders as o on c.c_id = o.c_id;
【例.66】查询fruits表,为f_name取别名fruit_name,f_price取别名fruit_price,为fruits表取别名f1,查询表中f_price < 8的水果的名称
select f1.f_name as fruit_name, f1.f_price as fruit_price from fruits as f1 where f1.f_price < 8;
【例.67】查询suppliers表中字段s_name和s_city,使用concat
函数连接这个两个字段值,并取列别名为suppliers_title
如果没有对连接后的值取别名,其显示列名称将会不够直观,输入如下sql
select concat(rtrim(s_name) , ' (', rtrim(s_city), ')') from suppliers order by s_name;
更多关于mysql相关内容感兴趣的读者可查看本站专题:《mysql常用函数大汇总》、《mysql日志操作技巧大全》、《mysql事务操作技巧汇总》、《mysql存储过程技巧大全》及《mysql数据库锁相关技巧汇总》
希望本文所述对大家mysql数据库计有所帮助。
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