Hello,experts
There has a SQL using DBLINK and its SQL_ID is '83gn36c1fu9dw' on my Oracle Data Guard 11.2.0.4.0 primary DB,
sql_fulltext is as follows,
SELECT *
FROM
(
SELECT \*
FROM
(
SELECT t.school\_id ,
t.school\_name,
t.photo\_path ,
r.subject\_id ,
r.version\_id ,
r.year\_mark ,
r.textbook\_code
FROM
(
SELECT \*
FROM sd\_res\_id\_case@res r2
WHERE :"SYS\_B\_0" =:"SYS\_B\_1"
**AND** rowid IN
(
SELECT **MIN**(rowid)
FROM sd\_res\_id\_case@res r1
WHERE r1.delete\_flag =:"SYS\_B\_2"
**AND** r1.is\_school\_check=:"SYS\_B\_3"
**AND** r1.subject\_id **IS NOT NULL**
**AND** r1.version\_id **IS NOT NULL**
**AND** r1.textbook\_code **IS NOT NULL**
GROUP BY r1.school\_id
HAVING **COUNT**(\*)\>=:"SYS\_B\_4"
)
)
r
LEFT JOIN base\_school t
ON r.school\_id = t.school\_id
WHERE :"SYS\_B\_5" =:"SYS\_B\_6"
**AND** t.county\_id =:1
)
a
WHERE rownum\<:"SYS\_B\_7"
)
WHERE rownum <= :2
and SQL code above using DBLINK part, it's another Oracle DB,i found it's LOAD has some high,please see my snapshot below,

At the same time,i use EMCC 12c(12.1.0.5.0) monitor platform to trace that FULL SQL execute process,
- Active Sessions,

- Top Activity

- SQL Monitor - Last Hour

- Monitored SQL Executions

- Execution Statistics

- Execution Plan

- another SQL execute completed,SQL Monitor some information


Now,how to optimize this complex SQL,please give me some guiding suggestions,Thanks!
Best Regards,
Quanwen Zhao