在Knex.js中使用MYSQL SET @

Question

I have been looking through the docs and online but can not find an example or any information on this.

Can you use SET with Knex.js? And if so, how? I want to create a ranked table, here is an example query from a tutorial. But I can not get SET to work.

SET @rank=0;

SELECT @rank:=@rank+1 AS rank, fruit, amount
  FROM sales
 ORDER BY amount DESC

Barmar's response got me on the right path of ranking using Knex.js. Here is my final Knex.js statement for those that are looking. I am able to create the table and list with it.

let schoolId = req.params.id;

knex.select(knex.raw('@rank:=@rank+1 AS rank'),'schools.SID',
knex.raw('ROUND(AVG(IF(reviews.active = 1,((Q1+Q2+Q3+Q4+Q5+Q6+Q7+Q8+Q9+Q10)/(10*10)*10), NULL)) ,1) AS average'))
.from('schools')
.joinRaw('CROSS JOIN (SELECT @rank := 0) AS vars')
.rightJoin('reviews', 'reviews.schoolID', 'schools.SID')
.where('schools.schoolCountry', '=', 'China')
.groupBy('schools.SID')
.orderByRaw('schools.SID DESC, schools.schoolCountryCode ASC ')
.then(function (rank) {
    console.log(rank);
    res.locals.ranking = rank;
    next();
}).catch(function (error) {
    console.log(error);
    res.send('An error occured');
});

Answer 1

It should work if knex.js keeps a database connection open between queries. Variables only persist within a database connection, so if it opens a new connection for each query the variable will be lost between the SET and SELECT .

But even if you can do it, a better way is to initialize the variable in the query itself:

SELECT @rank := @rank + 1 AS rank, fruit, amount
FROM sales
CROSS JOIN (SELECT @rank := 0) AS vars
ORDER BY amount DESC