有没有办法缩短这些查询？

I am just beginning, the following queries work but they seem to long and messy. How can I make these queries shorter?

Here is my code:

if ($result = $mysqli->query("select bestelling.datum,klant.klant_code,klant.adres,klant.naam,reis.bestemming,reis.klasse,reis.prijs_in_euro,reis.geannuleerd from klant,reis,bestelling where bestelling.bestelling_code = klant.klant_code and klant.klant_code = reis.reis_code"))


if ($stmt = $mysqli->prepare("UPDATE bestelling,klant,reis SET datum = ?, naam = ?, adres = ?, bestemming = ?, klasse = ?, prijs_in_euro = ?
        WHERE klant.klant_code=? and bestelling.bestelling_code = klant.klant_code and klant.klant_code = reis.reis_code"))


if($stmt = $mysqli->prepare("SELECT * FROM bestelling,klant,reis WHERE klant.klant_code=? and bestelling.bestelling_code = klant.klant_code and klant.klant_code = reis.reis_code"))

shorter could be not but more clear yes .. you should not use ancient join based on implicit where condition you should use explicit inner join

if ($result = $mysqli->query("
        select  bestelling.datum
                ,klant.klant_code
                ,klant.adres
                ,klant.naam
                ,reis.bestemming
                ,reis.klasse
                ,reis.prijs_in_euro
                ,reis.geannuleerd 
        from klant 
        INNER JOIN reis ON  klant.klant_code = reis.reis_code
        INNER JOIN bestelling ON  bestelling.bestelling_code = klant.klant_code 
        "))

and you could use alias of table name

if ($result = $mysqli->query("
        select  b.datum
                ,k.klant_code
                ,k.adres
                ,k.naam
                ,r.bestemming
                ,r.klasse
                ,r.prijs_in_euro
                ,r.geannuleerd 
        from klant k  
        INNER JOIN reis r ON  k.klant_code = r.reis_code
        INNER JOIN bestelling b  ON  b.bestelling_code = k.klant_code 
        "))

I recommend to use VIEW

VIEW is joined table. it makes your code so simple.

try this.

reference: https://www.w3schools.com/sql/sql_view.asp

create view all_info as select bestelling.datum,klant.klant_code,klant.adres,klant.naam,reis.bestemming,reis.klasse,reis.prijs_in_euro,reis.geannuleerd from klant,reis,bestelling where bestelling.bestelling_code = klant.klant_code and klant.klant_code = reis.reis_code

// same upper sql query.
select * from all_info;