python 的 mysql 连接组件 pymysql 如何使用轮询方式批量读取数据，以控制每次查询数据量，保护 db 的压力？
示例
思路是根据表的主键按照升序批量查询，然后下一次根据主键的偏移量范围升序批量查询，如此往复。
直接上代码：
import pymysql
def connect_db():
return pymysql.connect(
host='x.x.x.x',
port=3306,
user='xxx',
password='xxxx',
database='xxxxx',
charset='utf8'
)
def select_data_loop_cursor(conn: pymysql.Connection, table: str, id_field='id', fetch_fields='name', condition='1=1'):
# 元组结果列表
result_list = []
cursor = 0
fetch_size = 1000
loop = True
finished_count = 0
cur = conn.cursor()
while loop:
sql = 'SELECT {id}, {fetch_fields} FROM {table} WHERE {id} > {cursor} AND {condition} ' \
'ORDER BY {id} LIMIT {fetch_size}' \
.format(table=table,
id=id_field,
fetch_fields=fetch_fields,
cursor=cursor,
fetch_size=fetch_size)
cur.execute(sql)
result = cur.fetchall()
if result:
size = len(result)
if size < fetch_size:
loop = False
finished_count = finished_count + size
if finished_count % 2000 == 0:
print("finished count ======>", finished_count)
if size > 1:
# 返回多条记录时，两层元组
cursor = result[size - 1][0]
for t in result:
result_list.append(t)
else:
# 返回单条记录时，一层元组
cursor = result[0]
result_list.append(result)
cur.close()
return result_list
if __name__ == '__main__':
con = connect_db()
rl = select_data_loop_cursor(con, table='tb_demo_name')
con.close()
for r in rl:
print(r)
