mysql_09_合并查询_别名
USE db_book; SELECT id FROM t_book; SELECT id FROM t_booktype; #第五节:合并查询结果 #5.1:UNION #使用UNION关键字时,数据库系统会将所有的查询结果合并到一起,然后去除掉相同的记录; SELECT id FROM t_book UNION SELECT id FROM t_booktype; #5.2:UNION ALL #使用UNION ALL时,系统不会去除掉相同的记录。 SELECT id FROM t_book UNION ALL SELECT id FROM t_booktype; #第六节:为表和字段取别名 #6.1:为表取别名 #格式:表名 表的别名 SELECT * FROM t_book WHERE id=1; SELECT * FROM t_book t WHERE t.id=1; #6.2:为字段取别名 #格式:属性名 [AS] 别名 SELECT * FROM t_book WHERE id=1; SELECT id AS 编号,bookName AS 书名,price AS 价格,author AS 作者,bookTypeId AS 书类别 FROM t_book WHERE id=1;