database - query from multiple tables? -


hi started self-studying oracle sql, , stuck in following problem. glad if can guided on how approach solution these type of problem.

we have database. database consists of following tables:

table route_info contains descriptions of routes on monorails used travel.

route_info(route_no integer, source string, destination string, length integer, departs time, arrives time, cost integer);  +----------+----------+-------------+--------+----------+----------+------+ | route_no | source   | destination | length | departs  | arrives  | cost | +----------+----------+-------------+--------+----------+----------+------+ |     1462 | banglore | delhi       |   1516 | 13:00:00 | 15:00:00 | 4500 | |     4456 | gwalior  | delhi       |    543 | 05:05:06 | 04:55:24 |  546 | |     4524 | banglore | delhi       |   1516 | 04:44:00 | 13:00:45 | 1200 | |     7490 | banglore | gwalior     |   1343 | 01:16:17 | 17:07:08 | 1400 | |     7890 | agra     | gwalior     |    343 | 01:15:41 | 07:07:08 |  400 | +----------+----------+-------------+--------+----------+----------+------+

table monorail contains information each monorail.

monorail(rid integer, rname string, runningrange integer);  +------+---------------+--------------+ | rid  | rname         | runningrange | +------+---------------+--------------+ | 4454 | mark jung exp |          300 | | 1234 | speedester    |          454 | | 2134 | monstor       |         4054 | | 7334 | father        |         1051 | | 4444 | supreme       |         3023 | | 1444 | grain         |         3023 | +------+---------------+--------------+

table employee contains information of employees in organization (including drivers of monorails).

employee(eid integer, ename string, salary integer);  +------+--------+--------+ | eid  | ename  | salary | +------+--------+--------+ |  101 | nusrat |    100 | |  234 | emp1   |   5050 | |  323 | emp2   |   7050 | |  314 | emp3   |  10050 | |  541 | emp4   |   9010 | |  432 | emp5   |  12345 | |  123 | kabir  |    400 | |  555 | raheem |    235 | +------+--------+--------+

table assigned contains data monorail driven employee. can many-to-many relation.

assigned(eid integer, rid integer);  +------+------+ | eid  | rid  | +------+------+ |  101 | 4454 | |  234 | 1234 | |  323 | 1234 | |  314 | 1234 | |  314 | 2134 | |  541 | 2134 | |  123 | 7334 | |  101 | 4444 | |  101 | 1444 | +------+------+

we given following guidelines

  • make necessary assumptions.
  • string comparison case-insensitive.
  • always return result in increasing order of output.

now need write oracle sql query this: monorails "runningrange" greater 500, find id of rail ("rid") , sum of salary of drivers assigned rail.

break down smaller pieces make easier understand:
start getting monorails "runningrange" greater 500:

select rid monorail  runningrange > 500

then add inner join assigned table:

select m.rid monorail m inner join assigned on(m.rid = a.rid) runningrange > 500

then add inner join employee table:

select m.rid monorail m inner join assigned on(m.rid = a.rid) inner join employee e on(a.eid = e.eid) runningrange > 500

and add group by , sum.

select m.rid, sum(salary)  monorail m inner join assigned on(m.rid = a.rid) inner join employee e on(a.eid = e.eid) runningrange > 500 group m.rid order sum(salary)

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