mysql - Help with two SQL Queries -

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i’m having difficulties 2 queries. can of information problem lies in special conditions can’t seem right in sql statement.

the first query in natural language defined:

i’m going find candidates has acquired 2 qualifications during same time period, different institutes

my relational schema looks this:

bold = primary key

italics = foreign key

candidate = (candidateid, name, birth, mail)

qualification = (qualificationid, instituteid, candidateid, datestarted, datefinished, degreename, major)

institute = (instituteid, institutename, city)

the sql i’ve tried run not pretty (at point) , not working either is:

select (candidate.firstname, candidate.lastname)  candidate, qualification, institute  (select count(qualification.candidateid) qualification qualification.candidateid = 2)  , between qualification.datestarted , qualification.datefinished , qualification.instituteid <> qualification.instituteid

i gives me error , i’m pretty, in count clause can’t seem crack how count numbers of candidateid’s , set condition 2 (2) , i’m pretty sure there problem in checking on time period. have in same time period. , way, datestarted , datefinished in date format.

my second query i’m having problems in natural language formulated this:

find names of companies have made inquiries candidates average age below 30 (for candidates).

my relation schemas this:

candidate = (candidateid, name, birth, mail)

qualification = (qualificationid, instituteid, candidateid, datestarted, datefinished, degreename, major)

inquiry = (inquiryid,candidateid, companyid)

the query i’ve tried this:

select (company.companyname) company company, inquiry, candidates company.companyid = inquiry.companyid , inquiry.candidateid = candidate.candidateid , (select avg(candidate.birth < (right(curdate(),5<right(birth,5)) candidate)))

the birth tuble described date field.

i hope can me out whit these 2 queries , if there question 'em, please , i'll try clarify.

mestika

select  *    candidate c   exists         (         select  null            qualification q1         join    qualification q2         on      q2.candidateid = q1.candidateid                 , q2.datestarted = q1.datestarted                 , q2.dateended = q1.dateended                 , q2.instituteid <> q1.instituteid           q2.candidateid = c.candidateid         )

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