php 如何在 codeigniter 中对 COUNT 查询执行 num_rows()？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/11354802/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to do a num_rows() on COUNT query in codeigniter?
提问by TK123
This works:
这有效：
$sql = "SELECT id
FROM `users`
WHERE `account_status` = '" . $i . "'";
$query = $this->db->query($sql);
var_dump($query->num_rows());
But this doesn't:
但这不会：
$sql = "SELECT COUNT(*)
FROM `users`
WHERE `account_status` = '" . $i . "'";
$query = $this->db->query($sql);
var_dump($query->num_rows());
How to do a num_rows on a COUNT(*) query? Also is doing it the 2nd way any better performance wise?
如何对 COUNT(*) 查询执行 num_rows？也是以第二种方式做更好的性能吗？
回答by Steven Lu
Doing a COUNT(*)will only give you a singular row containing the number of rows and not the results themselves.
执行 aCOUNT(*)只会给你一个包含行数而不是结果本身的单行。
To access COUNT(*)you would need to do
要访问COUNT(*)你需要做的
$result = $query->row_array();
$count = $result['COUNT(*)'];
The second option performs much better since it does not need to return a dataset to PHP but instead just a count and therefore is much more optimized.
第二个选项的性能要好得多，因为它不需要将数据集返回给 PHP，而只是一个计数，因此更加优化。
回答by danneth
In CI it's really simple actually, all you need is
在 CI 中，它实际上非常简单，您只需要
$this->db->where('account_status', $i);
$num_rows = $this->db->count_all_results('users');
var_dump($num_rows); // prints the number of rows in table users with account status $i
回答by Varun Naharia
$query->num_rows()
The number of rows returned by the query. Note: In this example, $query is the variable that the query result object is assigned to:
查询返回的行数。注意：在本例中，$query 是查询结果对象分配给的变量：
$query = $this->db->query('SELECT * FROM my_table');
echo $query->num_rows();
回答by Chris Trahey
num_rows on your COUNT() query will literally ALWAYS be 1. It is an aggregate function without a GROUP BY clause, so all rows are grouped together into one. If you want the valueof the count, you should give it an identifier SELECT COUNT(*) as myCount ..., then use your normal method of accessing a result (the first, only result) and get it's 'myCount' property.
COUNT() 查询中的 num_rows 字面上总是 1。它是一个没有 GROUP BY 子句的聚合函数，因此所有行都组合在一起。如果你想要计数的值，你应该给它一个 identifier SELECT COUNT(*) as myCount ...，然后使用你的正常方法访问结果（第一个，唯一的结果）并获取它的 'myCount' 属性。
回答by Silambarasan R.D
As per CI Docswe can use the following,
根据CI Docs，我们可以使用以下内容，
$this->db->where('account_status', $i); // OTHER CONDITIONS IF ANY
$this->db->from('account_status'); //TABLE NAME
echo $this->db->count_all_results();
If we want to get total rows in the table without any condition, simple use
如果我们想在没有任何条件的情况下获取表中的总行数，简单使用
echo $this->db->count_all_results('table_name'); // returns total_rows presented in the table
回答by Alper Alver
$list_data = $this->Estimate_items_model->get_details(array("estimate_id" => $id))->result();
$result = array();
$counter = 0;
$templateProcessor->cloneRow('Title', count($list_data));
foreach($list_data as $row) {
$counter++;
$templateProcessor->setValue('Title#'.$counter, $row->title);
$templateProcessor->setValue('Description#'.$counter, $row->description);
$type = $row->unit_type ? $row->unit_type : "";
$templateProcessor->setValue('Quantity#'.$counter, to_decimal_format($row->quantity) . " " . $type);
$templateProcessor->setValue('Rate#'.$counter, to_currency($row->rate, $row->currency_symbol));
$templateProcessor->setValue('Total#'.$counter, to_currency($row->total, $row->currency_symbol));
}
回答by badcircle
I'd suggest instead of doing another query with the same parameters just immediately running a SELECT FOUND_ROWS()
我建议不要使用相同的参数进行另一个查询，而是立即运行 SELECT FOUND_ROWS()
回答by jay
This will only return 1 row, because you're just selecting a COUNT(). you will use mysql_num_rows()on the $queryin this case.
这只会返回 1 行，因为您只是选择了一个COUNT(). 在这种情况下，您将使用mysql_num_rows()on $query。
If you want to get a count of each of the ID's, add GROUP BY idto the end of the string.
如果您想获得每个ID's的计数，请添加GROUP BY id到字符串的末尾。
Performance-wise, don't ever ever ever use *in your queries. If there is 100 unique fields in a table and you want to get them all, you write out all 100, not *. This is because *has to recalculate how many fields it has to go, every single time it grabs a field, which takes a lot more time to call.
性能方面，永远不要*在您的查询中使用。如果表中有 100 个唯一字段，而您想获取所有字段，则写出全部 100 个，而不是*. 这是因为*必须重新计算它必须去多少个字段，每次它抓取一个字段时，这需要更多的时间来调用。
