Python daily practice - data storage sixth level: operating MySQL database

The sixth question of the interview:

Part 1 - Test Site:

Operate the MySQL database:

1. Create MySQL data table;
2. insert records into the table;
3. Other database operations.

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Part 2 - Interview Questions:

1. Interview question 1: How to create a MySQL data table?

2. Interview question 2: How to insert data into MySQL table?

3. Interview question 3: How to query data in MySQL?

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Part 3 - Analysis:

One of the interview questions to create a MySQL data table:

# coding=utf-8
# _author__ = 孤寒者

from pymysql import *

def connectDB():
    '''
    连接本地MySQL数据库，指定连接的库为test库。
    :return:
    '''
    db = connect(host='localhost', user='root', password='123456', port=3306, db='test')
    return db
db = connectDB()
print(type(db))

def createTable(db):
    c = db.cursor()
    try:
        c.execute('''create table persons
                    (id int primary key not null,
                    name text not null,
                    age int not null,
                    address char(100),
                    salary real);''')
        db.commit()
        db.commit()
        return True
    except:
        db.rollback()
    return False
if createTable(db):
    print('create table success')
else:
    print('create table failed')

Use the navicat tool to view:

Interview question 2 inserting data into MySQL table:

# coding=utf-8
# _author__ = 孤寒者

from pymysql import *

def connectDB():
    '''
    连接本地MySQL数据库，指定连接的库为test库。
    :return:
    '''
    db = connect(host='localhost', user='root', password='123456', port=3306, db='test')
    return db
db = connectDB()
print(type(db))


def insertRecords(db):
    cursor = db.cursor()
    try:
        cursor.execute("delete from persons")
        cursor.execute('''
        insert into persons(id,name,age,address,salary)
        values(1, 'GuHanZhe', 18, 'China', 9999)
        ''')
        cursor.execute('''
        insert into persons(id,name,age,address,salary)
        values(2, 'XiaoZhang', 55, 'China', 9)
        ''')
        db.commit()
        return True
    except Exception as e:
        print(e)
        db.rollback()
    return False

if insertRecords(db):
    print("成功插入记录")
else:
    print("插入记录失败")

Use the navicat tool to view:

Interview question 3: Query data in MySQL:

# coding=utf-8
# _author__ = 孤寒者
from pymysql import *

def connectDB():
    '''
    连接本地MySQL数据库，指定连接的库为test库。
    :return:
    '''
    db = connect(host='localhost', user='root', password='123456', port=3306, db='test')
    return db
db = connectDB()


def selectRecords(db):
    cursor = db.cursor()
    sql = 'select name,age,salary from persons order by age desc'
    cursor.execute(sql)
    results = cursor.fetchall()
    print(results)
    print(type(results))    # 打印发现是元组类型

selectRecords(db)
db.close()

• We found that the output type of the query data is a tuple type. What should we do if we want to pair the field name with the queried data?
• Here we need to use two very commonly used functions dict() and zip(), as follows:

# coding=utf-8
# _author__ = 孤寒者
import json

from pymysql import *

def connectDB():
    '''
    连接本地MySQL数据库，指定连接的库为test库。
    :return:
    '''
    db = connect(host='localhost', user='root', password='123456', port=3306, db='test')
    return db
db = connectDB()


def selectRecords(db):
    cursor = db.cursor()
    sql = 'select name,age,salary from persons order by age desc'
    cursor.execute(sql)
    results = cursor.fetchall()
    print(results)
    print(type(results))    # 打印发现是元组类型

    # 将字段名和查询结果整合在一起
    fields = ['name', 'age', 'salary']
    records = []
    for row in results:
        records.append(dict(zip(fields, row)))
    return json.dumps(records)      # 输出类型为JSON字符串


endresults = selectRecords(db)
print(endresults)
db.close()

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Part 4 - Conclusion:

• Note: We use the API in the pymysql module to operate the MySQL database, this module needs to be installed separately~