UNION函数的使用以及SQL文的高效编辑方法
Posted nichoo的博客
tags:
篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了UNION函数的使用以及SQL文的高效编辑方法相关的知识,希望对你有一定的参考价值。
查找SELECT 相同列的情况下,例如选择一个月每一天的某几项数据,相当于查询一个月三十行数据,为了在一个表中显示就要使用union函数。
eg:
SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-01%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-02%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-03%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-04%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-05%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-06%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-07%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-08%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-09%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-10%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-11%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-12%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-13%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-14%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-15%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-16%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-17%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-18%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-19%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-20%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-21%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-22%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-23%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-24%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-25%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-26%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-27%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-28%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-29%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-30%‘ AND act = ‘1005001001‘ UNION ALL SELECT COUNT(DISTINCT uid) AS c FROM da_track WHERE data_time LIKE ‘2018-05-31%‘ AND act = ‘1005001001‘
1. UNION 表示去重的结果;
2. UNION ALL 表示不进行去重的结果;
UNION函数就是用来拼表的,条件是每个选择语句的列相同,这个列的内容可能相同或者不同,不同的时候以第一个选择语句为准。
需求在哪?比如要使用拼接之后的表格,就很有用了,场景:一个月30天,求每一天去重的日活量,然后求和再做平均,这就需要将去重的日活拼接成一张30行的表,然后再做SUM然后再求平均。
根据实际需要使用UNION函数,使用SQL最重要的技能就是理解表格之间的关系,前后层次,你需要什么表格就使用连接JOIN、UNION等方法人为实现什么表格。
在重复查询的时候,一般都是修改一段SQL文的小部分语句,比如日期的天的数字,这种情况就需要掌握高级编辑方法来提高编辑效率,使用excel和高级文本编辑器(editplus等)以及正则化手段。
方法总结:
以上是关于UNION函数的使用以及SQL文的高效编辑方法的主要内容,如果未能解决你的问题,请参考以下文章
在具有相同架构的表上使用 UNION ALL 的 Google Big Query 中的 SQL 错误编辑:架构从 String 更改为 INT
sql union和union all的用法及效率 以及与join的区别
SQL Server-聚焦UNIOL ALL/UNION查询