随笔分类 -  SQL

Flask使用SQLAlchemy两种方式
摘要：一、SQLAlchemy和Alembic 主要使用原生的SQLAlchemy进行数据库操作和使用Alemic进行数据库版本控制 I 创建数据库主要有三个步骤 创建表的父类/数据库连接/Session 初始化每个表的class定义 class UserBaseModel(): __tablename_ 阅读全文
posted @ 2017-10-19 17:35 wilderness 阅读(4441) 评论(0) 推荐(0)
[mysql] update……from……
摘要：今天插入一条数据就像这样 然后报错： You can't specify target table 'categorys' for update in FROM clause 不能select同一个表中的某些值，然后update到同一个表中 然后修改如下： 重点在 select a.id from 阅读全文
posted @ 2017-08-28 15:32 wilderness 阅读(489) 评论(0) 推荐(0)
[MySQL-笔记]创建高性能索引
摘要：索引，MySQL中也叫“键”，是存储引擎中用于快速找到记录的一种数据结构，具体的工作方式就像书本中的索引一样，但是具体的实现方式会有差别。 一.索引分类 B-Tree索引： 优点： MyISAM中，索引根据数据的物理位置引用被索引的行，InnoDB中根据主键引用被索引的行。 B-Tree索引能够加快 阅读全文
posted @ 2017-03-28 23:24 wilderness 阅读(191) 评论(0) 推荐(0)
[SQL]197. Rising Temperature
摘要：Given a Weather table, write a SQL query to find all dates' Ids with higher temperature compared to its previous (yesterday's) dates. For example, ret 阅读全文
posted @ 2017-03-04 12:24 wilderness 阅读(215) 评论(0) 推荐(0)
[SQL]196. Delete Duplicate Emails
摘要：Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id. For example, aft 阅读全文
posted @ 2017-03-04 12:13 wilderness 阅读(174) 评论(0) 推荐(0)
【SQL】185. Department Top Three Salaries
摘要：The Employee table holds all employees. Every employee has an Id, and there is also a column for the department Id. The Department table holds all dep 阅读全文
posted @ 2017-03-03 23:33 wilderness 阅读(233) 评论(0) 推荐(0)
【SQL】184. Department Highest Salary
摘要：The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id. The Department table hol 阅读全文
posted @ 2017-03-03 23:16 wilderness 阅读(250) 评论(0) 推荐(0)
【SQL】183. Customers Who Never Order
摘要：Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything 阅读全文
posted @ 2017-03-03 12:21 wilderness 阅读(196) 评论(0) 推荐(0)
【SQL】182. Duplicate Emails
摘要：Write a SQL query to find all duplicate emails in a table named Person. 阅读全文
posted @ 2017-03-03 12:15 wilderness 阅读(115) 评论(0) 推荐(0)
【SQL】181. Employees Earning More Than Their Managers
摘要：The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id. Given the Em 阅读全文
posted @ 2017-03-03 12:10 wilderness 阅读(202) 评论(0) 推荐(0)
【SQL】180. Consecutive Numbers
摘要：Write a SQL query to find all numbers that appear at least three times consecutively. For example, given the above Logs table, 1 is the only number th 阅读全文
posted @ 2017-03-02 23:55 wilderness 阅读(226) 评论(0) 推荐(0)
【SQL】178. Rank Scores
摘要：Write a SQL query to rank scores. If there is a tie between two scores, both should have the same ranking. Note that after a tie, the next ranking num 阅读全文
posted @ 2017-03-02 23:53 wilderness 阅读(261) 评论(0) 推荐(0)
【SQL】177. Nth Highest Salary
摘要：Write a SQL query to get the nth highest salary from the Employee table. For example, given the above Employee table, the nth highest salary where n = 阅读全文
posted @ 2017-03-02 23:50 wilderness 阅读(234) 评论(0) 推荐(0)
【SQL】176. Second Highest Salary
摘要：Write a SQL query to get the second highest salary from the Employee table. For example, given the above Employee table, the second highest salary is  阅读全文
posted @ 2017-03-02 23:44 wilderness 阅读(178) 评论(0) 推荐(0)
【SQL】175. Combine Two Tables
摘要：Table: Person Table: Address Write a SQL query for a report that provides the following information for each person in the Person table, regardless if 阅读全文
posted @ 2017-03-02 23:43 wilderness 阅读(238) 评论(0) 推荐(0)