mySQL oef statistische functies

/* 16 */
    select count(*) as 'aantal planten' from planten
/* 17 */
    select count(*) from planten where kleurid is not null
/* 18 */
select count(*) from bestellingen where besteldatum is not null
/* 19 */
select count(*) from bestellingen where leverdatum is not null
/* 20 */
select count(distinct artcode) from offertes
/* 21 A */
select count(naam), woonplaats from leveranciers group by woonplaats
/* 21 B */
select avg(hoogte), sum(hoogte) /count(hoogte) from planten
/* 22 */
select levcode, count(artcode), levertermijn from offertes where levertermijn < 17 group by levcode having count(artcode)>=20 order by count(artcode) desc
/* 23 */
select bestelnr, aantal from bestellijnen group by bestelnr
/* 24 */
select min(offerteprijs) from offertes where artcode = 123
/* 25 */
select count(artcodelev) from offertes where artcodeLev = 'B111'
/* 26 */
select artcode, min(offerteprijs), max(offertePrijs) from offertes group by artcode
/* 27 */
select levertermijn, min(offerteprijs) from offertes group by levertermijn
/* 28 */
select naam from planten order by naam asc limit 1
/* 29 */
select count(*), woonplaats from leveranciers group by woonplaats having count(*)>=2 order by woonplaats