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?

greybeard · Accepted Answer · 2022-01-03 07:35:59Z

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 3, 2022 at 7:35

greybeard

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answered Jul 10, 2014 at 12:01

Rodrigo Medeiros

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7 Comments

Ben Fortune Over a year ago

if (!result.length) will work perfectly fine here.

Rodrigo Medeiros Over a year ago

@BenFortune Agreed, since Javascript evaluates false for 0. It's just that I like that verbose way of writing code.

Spock Over a year ago

Shouldn't it be (if result.isArray() && result.length > 0) ?? Anyway, Ben's "negative" is better

Akash Agarwal Over a year ago

@BenFortune It didn't work fine for me. What worked for me is if(result.length != 0) or greater than.

kojow7 Over a year ago

If result.length is greater than 0, why do you need to check for if result?

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