1. 查看主表是否设置主键。

2. 

SELECT ent.*, tab.num AS all_num FROM enterprise ent 
inner JOIN (SELECT se.enterprise_id, COUNT(se.ID) num FROM sebaseinfo se WHERE se.del_flag = 0 AND (se.install_district LIKE CONCAT('3703'::text, '%')) AND se.use_state = '1'
 GROUP BY se.enterprise_id) tab ON ent.ID = tab.enterprise_id 
WHERE (ent.del_flag = '0' AND ent.risk_level = '1级') order by id desc limit 50;

SELECT se.enterprise_id, COUNT(se.ID) num FROM sebaseinfo se WHERE se.del_flag = 0 AND (se.install_district LIKE CONCAT('3703'::text, '%')) AND se.use_state = '1'
 GROUP BY se.enterprise_id

count(se.id) 改成 count(*) 之后 提升速度。