大约有 41,000 项符合查询结果（耗时：0.0430秒） [XML]
Get top n records for each group of grouped results
...ould need to specify the group number and add queries for each group:
(
select *
from mytable
where `group` = 1
order by age desc
LIMIT 2
)
UNION ALL
(
select *
from mytable
where `group` = 2
order by age desc
LIMIT 2
)
There are a variety of ways to do this, see this articl...
Measure the time it takes to execute a t-sql query
... to just grab the current date and time.
In SQL Server Management Studio
SELECT GETDATE();
SELECT /* query one */ 1 ;
SELECT GETDATE();
SELECT /* query two */ 2 ;
SELECT GETDATE();
To calculate elapsed times, you could grab those date values into variables, and use the DATEDIFF function:
DECL...
Is it possible to center text in select box?
...you could style the dropdown:
https://www.filamentgroup.com/lab/jquery-ui-selectmenu-an-aria-accessible-plugin-for-styling-a-html-select.html
This plugin hides the select element, and creates span elements etc on the fly to display a custom drop down list style. I'm quite confident you'd be able t...
How to map and remove nil values in Ruby
...blem:
N = 1_00_000
enum = 1.upto(1_000)
Benchmark.bmbm do |x|
x.report("select + map") { N.times { enum.select { |i| i.even? }.map{|i| i + 1} } }
x.report("map + compact") { N.times { enum.map { |i| i + 1 if i.even? }.compact } }
x.report("filter_map") { N.times { enum.filter_map { |i| i ...
MySQL - Rows to Columns
...ms that I'll use for the rest of this post. This will be the base table:
select * from history;
+--------+----------+-----------+
| hostid | itemname | itemvalue |
+--------+----------+-----------+
| 1 | A | 10 |
| 1 | B | 3 |
| 2 | A | 9...
Any way to select without causing locking in MySQL?
...s/22-mysql-with-nolock.aspx
in MS SQL Server you would do the following:
SELECT * FROM TABLE_NAME WITH (nolock)
and the MYSQL equivalent is
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED ;
SELECT * FROM TABLE_NAME ;
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ ;
EDIT
Mic...
Getting only Month and Year from SQL DATE
...o 'discard' the Days, Hours, etc
- Leaving a year/month only date field
SELECT
DATEADD(MONTH, DATEDIFF(MONTH, 0, <dateField>), 0) AS [year_month_date_field]
FROM
<your_table>
This gets the number of whole months from a base date (0) and then adds them to that base date. Thus ...
Argument list too long error for rm, cp, mv commands
...der a directory in UNIX. The names of the PDFs are really long (approx. 60 chars).
27 Answers
...
How to get a number of random elements from an array?
...- Math.random());
// Get sub-array of first n elements after shuffled
let selected = shuffled.slice(0, n);
DEMO:
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Is there any difference between GROUP BY and DISTINCT
...CT and distinct by UNION cause an oracle error, but GROUP BY worked; I was selecting only 1 column from a view and not using any aggregation; I'm still baffled why it required it, but it does confirm there is some difference in the execution. As others point out, it also lets you GROUP BY columns no...