Database

作者: 瞬间流星 | 来源:发表于2018-05-18 11:08 被阅读0次

    1 Insert

    //添加一条数据
    Insert into Users(name,email) Values('AA','A@umich.edu')
    

    2 Delete

    //只删除符合where条件的数据
    
    DELETE FROM User WHERE email = 'ted@umich.edu'
    
    

    3 Update

    //将符合where条件的数据的name变量更改为AA
    UPDATE Users SET name = 'AA' where email ='A@umich.edu'
    

    4 Select

    //查找所有数据
    //查找符合where条件的数据
    SELECT*FROM Users
    SELECT*FROM Users WHERE email='A@umich.edu'
    
    //order用法,搜索所有email的数据
    SELECT*FROM Users OEDER BY email
    
    

    一个小项目

    import sqlite3
    
    conn = sqlite3.connect('emaildb.sqlite')
    cur = conn.cursor()
    
    cur.execute('''
                DROP TABLE IF EXISTS Counts''')
    
    cur.execute('''CREATE TABLE Counts(email TEXT,count INTEGER)''')
    
    fh = open('short.txt')
    
    for line in fh:
        if not line.startswith('From: '):continue
        pieces = line.split()
        email = pieces[1]
        cur.execute('SELECT count FROM Counts Where email = ?',(email,))
        row = cur.fetchone()
        if row is None:
            cur.execute('''INSERT INTO Counts (email,count)
            VALUES (?,1)''',(email,))
        else:
            cur.execute('Update Counts SET count = count +1 WHERE email =?',(email,))
        conn.commit()
    
    sqlstr = 'SELECT email,count FROM Counts ORDER BY count DESC LIMIT 10'
    
    for row in cur.execute(sqlstr):
        print (str(row[0]),row[1])
    cur.close()
    
    
    

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