简体中文(ZH-CN) English(EN) 繁体中文(ZH-TW) 日本語(JA) 한국어(KO) Melayu(MS) Français(FR) Deutsch(DE)
Home > Database > Mysql Tutorial > body text

循序渐进学Oracle之复杂查询(重点)

WBOY
Release： 2016-06-07 17:38:00
Original
1165 people have browsed it

前言在实际应用中经常需要执行复杂的数据统计,经常需要显示多张表的数据,故必须要高度重视:复杂的select语句!1-数据分组的重要函数:max、min、avg、sum、count(1

前言

在实际应用中经常需要执行复杂的数据统计,经常需要显示多张表的数据,故必须要

范例：

073703694.jpg

没有40部门，我们换成RIGHT JOIN…ON ，如下图所示：

073949376.jpg

由上可知：40部门出现了！

在Oracle之外的数据库（SQLSERVER、MYSQL、DB2等）都使用以上的SQL：1999语法操作，故必须要会！（当然，，一直使用Oracle数据库，就可以不会：））

再次强调：多表查询的性能肯定不高，而且性能一定要在大数据量的情况下，才能发现。


本文出自 “beyondhedefang” 博客，请务必保留此出处

Related labels：
Complex query
source：php.cn
Previous article： hbase安装 Next article： 在SQL 2012中使用和Oracle 一样的序列
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Latest Articles by Author
Latest Issues
The query and formula form the entire table, with new columns, where the new columns are formulas involving other conditional column values EDIT: The formula should be the "value" column - the "value" column wi...
From 2024-04-06 21:23:40
0
2
530
Calculate the sum of fields in another table using MySQL SQL query I have a schema like this: User table with attributes "user_id" and "userna...
From 2024-04-06 19:39:29
0
1
441
How to group and count in MySQL? I'm trying to write a query that extracts the total number of undeleted messages sent to f...
From 2024-04-06 18:30:17
0
1
353
MySQL gets data from multiple tables I have a eg_design table which contains the following columns: and eg_domains table which ...
From 2024-04-06 18:42:44
0
2
479
Record query under partial value conditions - SQL skill sharing I have a table called zipcode which has a column called code. The Code column contains the...
From 2024-04-06 16:01:26
0
1
395
Related Topics
More>
Popular Recommendations
Popular Tutorials
More>
Related Tutorials
Popular Recommendations
Latest courses
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template
About us Disclaimer Sitemap
php.cn：Public welfare online PHP training，Help PHP learners grow quickly！