在node.js mysql查询中，检查是否找不到匹配项 [英] In node.js mysql query, check if no matching found

问题描述

如何检查mysql(node.js)中是否找不到匹配项?

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:'
}

我的数据库不包含名称='abcd'.那么，如何检查查询是否不匹配?

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

推荐答案

作为查询的结果，您将收到一个空数组([])，因为如您所说，您的数据库不包含任何行与name = 'abcd' .

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'.

当您这样做:

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

，您将输入if，因为Javascript将true评估为[].看看此处的这篇文章，解释了Javascript如何评估true和false值.

, 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.

检查结果数组是否为空的更好方法是:

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

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

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