大约有 37,000 项符合查询结果（耗时：0.0358秒） [XML]
MIN/MAX vs ORDER BY and LIMIT
...king at an unindexed field, using MIN() requires a single full pass of the table. Using SORT and LIMIT requires a filesort. If run against a large table, there would likely be a significant difference in percieved performance. As a meaningless data point, MIN() took .36s while SORT and LIMIT took...
Fastest check if row exists in PostgreSQL
I have a bunch of rows that I need to insert into table, but these inserts are always done in batches. So I want to check if a single row from the batch exists in the table because then I know they all were inserted.
...
How does C compute sin() and other math functions?
...ximations for both sin(x) and cos(x), then using values from a precomputed table to refine the approximation.
When |x| > 2, none of the above algorithms would work, so the code starts by computing some value closer to 0 that can be fed to sin or cos instead.
There's yet another branch to deal wit...
TSQL - How to use GO inside of a BEGIN .. END block?
...t using SET NOEXEC.
IF not whatever
BEGIN
SET NOEXEC ON;
END
ALTER TABLE dbo.EMPLOYEE ADD COLUMN EMP_IS_ADMIN BIT NOT NULL
GO
UPDATE dbo.EMPLOYEE SET EMP_IS_ADMIN = whatever
SET NOEXEC OFF;
share
|
...
How to create a HashMap with two keys (Key-Pair, Value)?
...mply use:
Map<Key, V> map = //...
and:
map.get(new Key(2, 5));
Table from Guava
Table<Integer, Integer, V> table = HashBasedTable.create();
//...
table.get(2, 5);
Table uses map of maps underneath.
N dimensions
Notice that special Key class is the only approach that scales to...
How to vertically align elements in ?
...n, you're not worrying about IE or older browsers.
So you can use display:table-cell and display:table-row like so:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.or...
Why do we not have a virtual constructor in C++?
...uctor ends.In order for the constructor to be dispatched using the virtual table , there has to be an existing object with a pointer to the virtual table , but how can a pointer to the virtual table exist if the object still doesn't exist? :)
Logic reason
You use the virtual keyword when you want ...
How do I stop Entity Framework from trying to save/insert child objects?
...everything, EF seems to be still trying to insert into some of the related tables. At this point, I'm ready to rip EF out and switch back to SQL which at least behaves sensibly. What a pain.
– Mark Micallef
Aug 22 '14 at 8:29
...
Convert Unix timestamp into human readable date using MySQL
...
Use FROM_UNIXTIME():
SELECT
FROM_UNIXTIME(timestamp)
FROM
your_table;
See also: MySQL documentation on FROM_UNIXTIME().
share
|
improve this answer
|
follow
...
How do I check if a SQL Server text column is empty?
I am using SQL Server 2005. I have a table with a text column and I have many rows in the table where the value of this column is not null, but it is empty. Trying to compare against '' yields this response:
...