大约有 40,000 项符合查询结果（耗时：0.0481秒） [XML]
MySQL COUNT DISTINCT
...
Select
Count(Distinct user_id) As countUsers
, Count(site_id) As countVisits
, site_id As site
From cp_visits
Where ts >= DATE_SUB(NOW(), INTERVAL 1 DAY)
Group By site_id
...
How to add column if not exists on PostgreSQL?
...s, _col text, _type regtype)
RETURNS bool AS
$func$
BEGIN
IF EXISTS (SELECT 1 FROM pg_attribute
WHERE attrelid = _tbl
AND attname = _col
AND NOT attisdropped) THEN
RETURN FALSE;
ELSE
EXECUTE format('ALTER TABLE %s ADD COLUMN %I %s...
What columns generally make good indexes?
...earching the results speedily from tables. So it is most important step to select which columns to be indexed. There are two major places where we can consider indexing: columns referenced in the WHERE clause and columns used in JOIN clauses. In short, such columns should be indexed against which yo...
phpcms与ucenter整合常见问题与解答 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...1536000;
$uid = intval($get['uid']);
$query = DB::query("SELECT uid, username, password FROM ".DB::table('common_member')." WHERE uid='$uid'");
if ($member = DB::fetch($query))
{
dsetcookie('auth', authcode("$member[password]\t$member[uid]", 'ENCODE')...
Transaction isolation levels relation with locks on table
... writes data and commit/rollback (depending on results). B just executes a SELECT statement to read data. C reads and updates data. All these process work on the same table T.
READ UNCOMMITTED - no lock on the table. You can read data in the table while writing on it. This means A writes data (unc...
Is it possible to select the last n items with nth-child?
Using a standard list, I'm trying to select the last 2 list items. I've various permutations of An+B but nothing seems to select the last 2:
...
How can I change the file type association of an existing file in WebStorm?
...t patterns by which a file gets associated as some type or other.
If you select the patterns for a file type you have wrongly selected (in your case Text type) you can remove the filename pattern with which was created to associate you file's filename as a wrong type.
Then click Apply > OK
...
String concatenation in MySQL
...most DBMSs use of + or || for concatenation. It uses the CONCAT function:
SELECT CONCAT(first_name, " ", last_name) AS Name FROM test.student
As @eggyal pointed out in comments, you can enable string concatenation with the || operator in MySQL by setting the PIPES_AS_CONCAT SQL mode.
...
Why there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT clause?
...pdated) values(null, null);
Query OK, 1 row affected (0.06 sec)
mysql> select * from t5;
+----+---------------------+---------------------+
| id | stamp_created | stamp_updated |
+----+---------------------+---------------------+
| 2 | 2009-04-30 09:44:35 | 2009-04-30 09:44:35 |
+...
List of encodings that Node.js supports
...r.gz
gyp http 200 http://nodejs.org/dist/v0.10.1/node-v0.10.1.tar.gz
xcode-select: Error: No Xcode is selected. Use xcode-select -switch <path-to-xcode>, or see the xcode-select manpage (man xcode-select) for further information.
fs.readFileSync() returns a Buffer if no encoding is specified...