import psycopg2

# establishing the connection
conn = psycopg2.connect(
   database="CONNE py",
    user='postgres',
    password='asdf',
    host='localhost',
    port= '5432'
)

cursor=conn.cursor()

tables = ["Class_A", "Class_B", "Class_C"]

outer_dict={}

for table in tables:
    cursor.execute(f'SELECT name, department, overall_percentage FROM {table}')
    rows=cursor.fetchall()

    inner_dict={}

    for row in rows:
        name, department, overall_percentage=row

        inner_dict={
            'name':name,
            'department':department,
            'overall_percentage':overall_percentage
            }
        outer_dict[table]=inner_dict


print(outer_dict)
cursor.close()

这是我现有的代码，在运行这个程序时，对于每个表，我只会得到该表的最后一条数据作为输出。

this is the output:

{'Class_A': {'name': 'Ranga', 'department': 'MCA', 'overall_percentage': 72}, 'Class_B': {'name': 'Delli', 'department': 'MBA', 'overall_percentage': 62}, 'Class_C': {'name': 'Mohan', 'department': 'B.tech AI', 'overall_percentage': 92}}

But i need all the data to be printed like this below ( example output for class A only)

     {'Class_A': {{'name': 'Ranga', 'department': 'MCA', 'overall_percentage': 72}, {'name': 'Ranga', 'department': 'MCA', 'overall_percentage': 72}, {'name': 'Ranga', 'department': 'MCA', 'overall_percentage': 72}, }

And I'm new to programming can any one explain me what i did wrong

解决方案

看起来你在每次遍历行时都在覆盖outer_dict[table]。我建议定义一个列表，用来把所有字典追加进去，然后再把它追加到那里。

我建议使用索引作为键：

outer_dict[table] = {}
for i, row in enumerate(rows):
    name, department, overall_percentage = row
    outer_dict[table][i] = {
        'name': name,
        'department': department,
        'overall_percentage': overall_percentage
    }

编辑：我还要指出，你想要的结构在Python中并不有效，集合不能包含字典。照上面的做法，你的输出将会是这样的：

{'Class_A': {0: {...}, 1: {...}, 2: {...}}}