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构建高并发高可用的电商平台架构实践 - 更多技术 - 清泛网 - 专注C/C++及内核技术
构建高并发高可用的电商平台架构实践一、 设计理念1. 空间换时间1) 多级缓存，静态化客户端页面缓存（http header中包含Expires Cache of Control，last modified(304，...一、 设计理念
1. 空间换时间
1) 多级缓存，静态化
客户端页面缓...
Can I concatenate multiple MySQL rows into one field?
... your needs. To calculate and assign the value:
SET group_concat_max_len = CAST(
(SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
FROM peoples_hobbies
GROUP BY person_id)
AS UNSIGNED
);
share
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Difference between numeric, float and decimal in SQL Server
...link:
"I frequently do calculations against decimal values. In some cases casting decimal values to float ASAP, prior to any calculations, yields better accuracy. "
http://sqlblog.com/blogs/alexander_kuznetsov/archive/2008/12/20/for-better-precision-cast-decimals-before-calculations.aspx
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Extract date (yyyy/mm/dd) from a timestamp in PostgreSQL
...
You can cast your timestamp to a date by suffixing it with ::date. Here, in psql, is a timestamp:
# select '2010-01-01 12:00:00'::timestamp;
timestamp
---------------------
2010-01-01 12:00:00
Now we'll cast it to a ...
Why doesn't Java support unsigned ints?
...tially can be treated as an unsigned integer. You would have to explicitly cast arithmetic operations back into char, but it does provide you with a way to specify unsigned numbers.
char a = 0;
char b = 6;
a += 1;
a = (char) (a * b);
a = (char) (a + b);
a = (char) (a - 16);
b = (char) (b % 3);
b = ...
SQL: IF clause within WHERE clause
...his without any IF or CASE
WHERE
(IsNumeric(@OrderNumber) AND
(CAST OrderNumber AS VARCHAR) = (CAST @OrderNumber AS VARCHAR)
OR
(NOT IsNumeric(@OrderNumber) AND
OrderNumber LIKE ('%' + @OrderNumber))
Depending on the flavour of SQL you may need to tweak the casts on the orde...
SSL Error When installing rubygems, Unable to pull data from 'https://rubygems.org/
...ws note
The Ruby Installer builds for windows are prepared by Luis Lavena and the path to certificates will be showing something like C:/Users/Luis/... check https://github.com/oneclick/rubyinstaller/issues/249 for more details and this answer https://stackoverflow.com/a/27298259/497756 for fix.
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Spring ApplicationContext - Resource leak: 'context' is never closed
...
A simple cast solves the issue:
((ClassPathXmlApplicationContext) fac).close();
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Efficiently convert rows to columns in sql server
... + 'SELECT ''INSERT INTO @ColumnListWithActions VALUES ('' + CAST( ROW_NUMBER() OVER (ORDER BY [NAME]) as nvarchar(10)) + '', '' + '''''''' + [NAME] + ''''''''+ '', ''''S'''');'''
+ 'FROM [' + @DB_Name + '].sys.columns '
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How to concatenate columns in a Postgres SELECT?
...n any case.
For non-string data types, you can "fix" the 1st statement by casting at least one argument to text. (Any type can be cast to text):
SELECT a::text || b AS ab FROM foo;
Judging from your own answer, "does not work" was supposed to mean "returns NULL". The result of anything concatena...