Create a for loop within a MySQL query

Question

My query is:

connection.query("SELECT * FROM posts WHERE someId = 2", (err, rows) => {

    allIds = [];

            for(var i = 1; i <= rows.length; i++){
                allIds.push(rows.id_post)
            }

             res.send("The IDs : " + allIds )
});

rows.length = 5, I'm getting the response: The IDs : , , , , ,. There is no data. I need all the IDs listed. Later want to run another query with those Ids, maybe in the same query but for now why aren't the IDs showing? What am I missing?

jetblack · Accepted Answer · 2017-09-19 13:13:21Z

1

It seems like 'rows.id_post' is undefined. Are you sure there is a property named 'id_post'? Is rows a json or an array? If it's an array you need:

for(var i = 0; i < rows.length; i++){
        allIds.push(rows[i].id_post)
    }

This should answer your question.

answered Sep 19, 2017 at 13:13

jetblack

1557 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Somename Over a year ago

Thanks. So what's causing i<=rows.length to fail and < to pass? Did that or i=0 is resolving this?

jetblack Over a year ago

arrays are 0 indexed. so the object array[array.lenght] doesn't exist.

Somename Over a year ago

Can you help me with stackoverflow.com/questions/46302496/… please. Same query extended.

Daniel Sampson · Accepted Answer · 2017-09-19 13:09:13Z

0

for(var i = 1; i <= rows.length; i++){
            allIds.push(rows.id_post)
        }

You're not referencing the index of the rows results... I'm not familiar with the Node.JS syntax but I would think you need to reference the i row to get the value to push...

answered Sep 19, 2017 at 13:09

Daniel Sampson

1116 bronze badges

2 Comments

Somename Over a year ago

You mean allIds.push(rows[i].id_post)? I tried that and get error : TypeError: Cannot read property 'id_comment' of undefined

Daniel Sampson Over a year ago

try this: connection.query("SELECT * FROM posts WHERE someId = 2", function selectAll(err, rows, fields) {

Collectives™ on Stack Overflow

Create a for loop within a MySQL query

2 Answers 2

3 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related