大约有 43,000 项符合查询结果（耗时：0.0372秒） [XML]
MySQL select 10 random rows from 600K rows fast
How can I best write a query that selects 10 rows randomly from a total of 600k?
26 Answers
...
Postgres: INSERT if does not exist already
...onditional INSERT in PostgreSQL:
INSERT INTO example_table
(id, name)
SELECT 1, 'John'
WHERE
NOT EXISTS (
SELECT id FROM example_table WHERE id = 1
);
CAVEAT This approach is not 100% reliable for concurrent write operations, though. There is a very tiny race condition between...
Select multiple images from android gallery
... am trying to achieve is opening the Gallery in Android and let the user select multiple images . Now this question has been asked frequently but i'm not satisfied with the answers. Mainly because i found something interesting in de docs in my IDE (i come back on this later) and thereby i don't...
How to remove all whitespace from a string?
...paces before, after and in between
" \u2190 \u2192 ", # contains unicode chars
paste0( # varied whitespace
whitespace,
"x",
whitespace,
"y",
whitespace,
collapse = ""
),
NA # missing
)
## [1] " x y "
#...
SQL JOIN and different types of JOINs
...
There are relatively new LATERAL JOIN .. SELECT * FROM r1, LATERAL fx(r1)
– Pavel Stehule
Jul 30 '13 at 11:52
13
...
What is a regular expression for a MAC Address?
... The second will incorrectly match strings which contain non-hex characters such as g.
– Binary Phile
Feb 25 '15 at 15:32
...
How can you programmatically tell an HTML SELECT to drop down (for example, due to mouseover)?
How can you programmatically tell an HTML select to drop down (for example, due to mouseover)?
12 Answers
...
Lost my schema.rb! Can it be regenerated?
... answered Oct 17 '16 at 2:18
R.ChaR.Cha
63566 silver badges1212 bronze badges
...
SQL Server SELECT LAST N Rows
...d database... Now let us retrieve the Last 5 orders placed by Employee 5:
SELECT ORDERID, CUSTOMERID, OrderDate
FROM
(
SELECT ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY OrderDate DESC) AS OrderedDate,*
FROM Orders
) as ordlist
WHERE ordlist.EmployeeID = 5
AND ordlist.OrderedDate &...
How to select the first element in the dropdown using jquery?
I want to know how to select the first option in all select tags on my page using jquery.
9 Answers
...