大约有 40,000 项符合查询结果（耗时：0.0354秒） [XML]
postgresql COUNT(DISTINCT …) very slow
...
You can use this:
SELECT COUNT(*) FROM (SELECT DISTINCT column_name FROM table_name) AS temp;
This is much faster than:
COUNT(DISTINCT column_name)
share
...
Why use the INCLUDE clause when creating an index?
...ot in the WHERE/JOIN/GROUP BY/ORDER BY, but only in the column list in the SELECT clause.
The INCLUDE clause adds the data at the lowest/leaf level, rather than in the index tree.
This makes the index smaller because it's not part of the tree
INCLUDE columns are not key columns in the index, so th...
How can I return pivot table output in MySQL?
...OUP BY.
The basic SQL providing this pivot can look something like this:
SELECT P.`company_name`,
COUNT(
CASE
WHEN P.`action`='EMAIL'
THEN 1
ELSE NULL
END
) AS 'EMAIL',
COUNT(
CASE
WHEN P.`action`='PRINT' AND...
SQLite UPSERT / UPDATE OR INSERT
... at this code:
INSERT INTO players (id, name, age)
VALUES (
coalesce((select id from players where user_name='steven'),
(select max(id) from drawings) + 1),
32)
The trick is in coalesce. It returns the id of the user 'steven' if any, and otherwise, it returns a new fresh id.
...
Restore LogCat window within Android Studio
...e bottom). Use the "gear" at the extreme top right of the log cat section; select floating mode. Confusingly it then "appears to be docked" still ... just grab the bar and move it around. (If you're used to Mac, it's a little confusing.) (Android Studio is awesome on Mac eh??)
...
How do I bind to list of checkbox values with AngularJS?
...repeat="fruitName in fruits">
<input
type="checkbox"
name="selectedFruits[]"
value="{{fruitName}}"
ng-checked="selection.indexOf(fruitName) > -1"
ng-click="toggleSelection(fruitName)"
> {{fruitName}}
</label>
And the appropriate controller code would be:
...
How to change Xcode Project name
...
For Xcode 4 or later:
Open a project
Select Project Navigator
Highlight project name
Single click on project name
For Xcode 3:
Open a project > Menu > Project > Rename ...
...
“A project with an Output type of Class Library cannot be started directly”
...oject in Solution Explorer -> Properties.
In opened tab with properties select Application and there will be ComboBox marked with Output Type label.
share
|
improve this answer
|
...
Selecting the first “n” items with jQuery
With Jquery, I need to select just the first "n" items from the page, for example the first 20 links instead of selecting all of them with the usual
...
How to set timeout on python's socket recv method?
...
The typical approach is to use select() to wait until data is available or until the timeout occurs. Only call recv() when data is actually available. To be safe, we also set the socket to non-blocking mode to guarantee that recv() will never block indef...