In node.js mysql query, check if no matching found

Question

How can I check if no matching found in mysql (node.js)?

mysql.query("select * from table1 where name = 'abcd'", function(error, result, field) {
    if(error) {
        exist(error); //No error
    } else if(result) {
        console.log(result);  //displays '[]'
        exist(null, result);
    } else {
        exist(null, null); //It is never execute
    }
});
function exist(error, result) {
    if(result)
        console.log("Test:"+result); //Executed and displays 'Test:'
}

My database does not contains name = 'abcd'. So, how can I check if the query does not match?

score 28 · Accepted Answer · edited Jan 03 '22 at 07:35

28

You're receiving an empty array ([]) as result of your query, because as you said, your database does not contain any row with name = 'abcd'.

When you do:

if (result) {
  if (result)
    console.log("Test:" + result);

, you'll enter the if, because JavaScript evaluates true for []. Take a look at this article here, that explains how JavaScript evaluates true and false values.

A better way to check if your result array is empty is to do:

if (result.length > 0) {
  if (result)
    console.log("Test:" + result);

edited Jan 03 '22 at 07:35

greybeard

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answered Jul 10 '14 at 12:01

Rodrigo Medeiros

7,814
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4

`if (!result.length)` will work perfectly fine here. – Ben Fortune Jul 10 '14 at 12:47
@BenFortune Agreed, since Javascript evaluates `false` for `0`. It's just that I like that verbose way of writing code. – Rodrigo Medeiros Jul 10 '14 at 13:01
Shouldn't it be ```(if result.isArray() && result.length > 0) ```?? Anyway, Ben's "negative" is better – Spock Jun 17 '15 at 09:13
@BenFortune It didn't work fine for me. What worked for me is `if(result.length != 0)` or greater than. – Akash Agarwal Mar 30 '16 at 21:07
7

If `result.length` is greater than 0, why do you need to check for `if result`? – kojow7 Oct 12 '17 at 02:46
If you are paranoid, then it should be `if (result && result.isArray() && result.length > 0) ...` There are times when the result is `null` but there was no `error` either. – Jesse Chisholm Feb 05 '20 at 00:32
To validate that the `result` is an array, use: `Array.isArray(result)` – alditis Jul 02 '21 at 04:35

In node.js mysql query, check if no matching found

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