javascript - JS function to count rows in SQLite table - Stack Overflow

admin管理员组

文章数量:1399997

I'm trying to make a JS function that counts rows in an SQLite table.

function countRows(){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            alert(len);
        });
    });
}

The above code displays an alert with numbers of rows in the table. However, I'd like to make a function that would return the number instead of showing the alert box.

I tried:

function countRows(){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            return len;
        });
    });
}

And then:

var number = countRows();
alert (number); // returns "undefined"

The above example returns "undefined", whereas a parallel example works fine:

function count(){
    return 3;
}
var number = count();
alert (number); // returns 3

I want to assign the number to a variable, so I could then make another sql query, count rows in another table, and pare the two results.

In PHP this would be:

$sql1 = mysql_query('SELECT COUNT(*) FROM table1');
$rows1 = mysql_result($sql1, 0);
$sql2 = mysql_query('SELECT COUNT(*) FROM table2');
$rows2 = mysql_result($sql2, 0);
if ($row1>$row2){}

I'm trying to make a JS function that counts rows in an SQLite table.

function countRows(){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            alert(len);
        });
    });
}

The above code displays an alert with numbers of rows in the table. However, I'd like to make a function that would return the number instead of showing the alert box.

I tried:

function countRows(){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            return len;
        });
    });
}

And then:

var number = countRows();
alert (number); // returns "undefined"

The above example returns "undefined", whereas a parallel example works fine:

function count(){
    return 3;
}
var number = count();
alert (number); // returns 3

I want to assign the number to a variable, so I could then make another sql query, count rows in another table, and pare the two results.

In PHP this would be:

$sql1 = mysql_query('SELECT COUNT(*) FROM table1');
$rows1 = mysql_result($sql1, 0);
$sql2 = mysql_query('SELECT COUNT(*) FROM table2');
$rows2 = mysql_result($sql2, 0);
if ($row1>$row2){}

• javascript
• sqlite

Share Improve this question Follow edited Mar 22, 2012 at 15:14 lukeshek asked Mar 22, 2012 at 14:13 lukesheklukeshek 97822 gold badges99 silver badges1717 bronze badges

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 4

You would be served much better by changing your query.

SELECT COUNT(ID) FROM table

Plus, its an async call so that the call return is returning the callback function. You should pass your own callback function.

function countRows(callback){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            callback(len);
        });
    });
}

db.transaction is asynchronous. returning value isn't assigned to any variable in code above. Solution is to pass callback or create custom event, which is almost the same.

Something like this:

function countRows(cb){
    db.transaction(function (tx){
        tx.executeSql('SELECT id FROM table', [], function (tx, results) {
            var len = results.rows.length;
            cb.call(this, len);
        });
    });
}

countRows(function (num) {alert(num)});

本文标签： javascriptJS function to count rows in SQLite tableStack Overflow