sqlite3自定义聚合函数

import sqlite3

class custom_concat:
    def __init__(self):
        self.retval=[]
    def step(self,value):
        self.retval.append(value)
    def finalize(self):
        return ','.join(self.retval)

# 连接 SQLite 数据库
conn = sqlite3.connect(':memory:')
conn.create_aggregate("custom_concat", 1, custom_concat)

# 示例查询
conn.execute('''
CREATE TABLE users (
    type TEXT,
    v TEXT
);''')
for i in range(3):
    conn.execute(f'''INSERT INTO users (type,v) VALUES ("a",{i})''')
for i in range(3):
    conn.execute(f'''INSERT INTO users (type,v) VALUES ("b",{i})''')
print(conn.execute('''
SELECT type,custom_concat(v) FROM users group by type;''').fetchall())
#[('a', '0,1,2'), ('b', '0,1,2')]