Get number of rows in cursor ? (equivalent to psycopg2#cursor.rowcount)

• asyncpg version: 0.15
• PostgreSQL version: 9.6
• Python version: 3.6.5
• Platform: Debian Buster
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: no
• Can the issue be reproduced under both asyncio and uvloop?: N/A

Warning: It's may be a duplicate of #311

I would like to get the number of rows from the last query (a SELECT query). An equivalent to cursor.rowcount in psycopg2.

I saw in #311 that we can get the query status line (as a string) from execute function. Actually, I'm not able to use it since I need a cursor. Don't know very well binary protocol of pg.. I don't even know if it is possible to get it.

The purpose of this issue is to avoid doing multiple queries (for instance with count(*) statement).

先从游标 API 和 execute 函数开始，然后查看 issue 中引用的 PostgreSQL 状态行行为。确定游标是否可以在不执行额外 count(*) 查询的情况下提供其上一次 SELECT 返回的行数，并为所请求的行为添加覆盖测试。