mysql | 易学教程

Following query taking too long to execute. How to optimize it

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问题 I use the following query to get years and the number of movies released in that year which(referring to a movie) has a female actor. It executes successfully, but it is taking 4 minutes to execute. How do I get results in less time? Also, my disk use goes to more than 70% during this execution. SELECT m.year, COUNT(m.id) FROM movies m JOIN roles r ON m.id=r.movie_id JOIN actors a ON r.actor_id=a.id WHERE a.gender='F' GROUP BY m.year; 回答1: I think you can use EXISTS instead of JOIN. SELECT m

DatabaseError : “not all arguments converted during string formatting” when I use pandas.io.sql.to_sql()

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问题 I have a table: And I try to use this import this table by sqlalchemy , the code is: import sqlalchemy as db import pandas.io.sql as sql username = 'root' password = 'root' host = 'localhost' port = '3306' database = 'classicmodels' engine = db.create_engine(f'mysql+pymysql://{username}:{password}@{host}:{port}/{database}') con = engine.raw_connection() #readinto dataframe df = pd.read_sql(f'SELECT * FROM `{database}`.`offices`;', con) print(df[:2]) df_append = pd.DataFrame([{'officeCode': 8,

高项真题及解析：信息系统项目管理师2020年11月上午真题及答案解析

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点击领取>>>软考 16本电子版官方教材 & 36本辅导教材 + 27套官方真题冲刺卷 + 21套必考知识点6G资料包 2020 下半年信息系统项目管理师上午真题及答案 1 、（）使系统的描述及信息模型的表示与客观实体相对应，符合人们的思维习惯，有利于系统开发过程中用户与开发人员的交流和沟通。 A ．原型化方法 B ．面向对象方法 C ．结构化方法 D ．面向服务的方法答案： B 解析：面向对象方法使系统的描述及信息模型的表示与客观实体相对应，符合人们的思维习惯，有利于系统开发过程中用户与开发人员的交流和沟通。 2 、 TCP/IP 模型中，（）协议属于网络层的协议。 A ． ARP B ． SNMP C ． TCP D ． FTP 答案： A 解析： TCP/IP 模型中，网络层中的协议主要有 IP （互联网协议）、 ICMP （网际控制报文协议）、 IGMP 、 ARP （地址解析协议）和 RARP （反向地址解析协议）等。 3 、（）不属于关系型数据库。 A ． Oracle B ． MySQL C ． SQL Server D ． MongoDB 答案： D 解析：常见的数据库管理系统主要有 Oracle 、 MySQL 、 SQLServer 、 MongoDB 等，这些数据库中，前三种均为关系型数据库，而 MongoDB 是非关系型的数据库。 4

Data Submit Interruption of html Form inserting data in mysql

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问题 I have this problem where in my Applicant Quiz using php, javascript, mysql. Its a simple quiz created from html forms, with a .php for inserting in the database for the applicants answer. It has a timer of 10 minutes that auto-submits the form and sets the value of 0 to blank fields and get inserted into the database. But the problem here is, sometimes, when submitting, it was not get inserted into the database, but sometimes it was succesfully submitted, I am using WAMP server, I have a

Using Python variables in MySQL insert statement

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问题 I've been trying for a while now and have look online and can't figure it out. Variables are numbers and animals sql = ("INSERT INTO favourite (number, info) VALUES (numbers, animals )") cursor.execute(*sql) conn.comit() 回答1: Use: sql=("INSERT INTO favourite (number, info) VALUES ({},{})".format(numbers,animals)) Its always good to use format as per future references. Check https://docs.python.org/release/3.1.5/library/stdtypes.html#old-string-formatting-operations 回答2: sql = ("INSERT INTO

Using Python variables in MySQL insert statement

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How to find rows>columns combinations with Cross Join? [SQL]

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问题 I want to create a combination of items from different categories ids. Can you help me? table +---------+-------------+------------+ | post_id | category_id | post_title | +---------+-------------+------------+ | 1 | 1 | Red | | 2 | 1 | Black | | 3 | 2 | Medium | | 4 | 3 | Male | | 5 | 3 | Female | +---------+-------------+------------+ The query results I want is as follows: Red-Medium-Male Black-Medium-Male Red-Medium-Female Black-Medium-Female For example, if there were items belonging to

store captured image in MySQL database with Python and OpenCV

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问题 I have a piece of code here which captures an image from my internal webcam on my laptop. With this image, i would like to directly send it to my MySQL database. here is the code. import numpy as np import cv2 import mysql.connector from mysql.connector import errorcode from time import sleep import serial # Obtain connection string information from the portal config = { 'host':'oursystem.mysql.database.azure.com', 'user':'user', 'password':'pass', 'database':'projectdb' } try: conn = mysql

How to set Collation in MySQL database with Django 2.* mysqlclient?

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问题 I need to set default Collation for MySQL tables with Django 2.*, im using mysqlclient, my settings are: DATABASES = { 'default': { 'ENGINE': 'django.db.backends.mysql', 'NAME': '', 'USER': '', 'PASSWORD': '', 'HOST': 'localhost', 'PORT': '3306', 'OPTIONS': { 'charset': 'utf8mb4', }, } } 'charset': 'utf8mb4', This parameter seems don't work properly and tables in DB utf8. Although i want to manually set and tables Collation to utf8mb4_general_ci Will be appreciate for any clues. 回答1: 'default

How to set Collation in MySQL database with Django 2.* mysqlclient?

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