检查哪些ID已过账

问题描述

检查PostgreSQL表中存在哪些ID的速度如何

我写了以下函数，但当len(x)大于500 000时，它会非常慢

import psycopg2
conn = psycopg2.connect(...)
cursor = conn.cursor(cursor_factory=psycopg2.extras.DictCursor)

def check_exist(lst):
    exist = []
    not_exist = []
    for i in lst:
        cursor.execute(f"SELECT * FROM table1 where id={i}")
        row = cursor.fetchone()
        if row:
            exist.append(i)
        else:
            not_exist.append(i)
    return exist, not_exist

x, y = check_exist(['2','4','3000','50000','10000000'])

推荐答案

您可以使用ANY，让postgres完成大部分工作：

import psycopg2, time
# database is in a datacenter just using a tunnel!
conn = psycopg2.connect("dbname=mf port=5959 host=localhost user=mf_usr")
cur = conn.cursor()

ids = [x for x in range(0, 750000)]

sql = """
    SELECT array_agg(id) from __users where id = ANY(%s);
"""
# array_agg: Postgres returns an array of ids!

_start = time.time()
cur.execute(sql, (ids, ))
existingIds = cur.fetchone()[0]
missingIds = set(ids) - set(existingIds)

print(len(existingIds))
print(len(missingIds))
print('Took: %.6f seconds' % (time.time() - _start))

输出：

284365
465635
Took: 5.564851 seconds

注意：确保ID列上有索引