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新闻传播中如何让沉默的数据说话 - 资讯 - 清泛网 - 专注C/C++及内核技术
新闻传播中如何让沉默的数据说话大数据时代，以数字化为基础的大数据技术正与互联网一起重塑媒体生态。那么，大数据怎样影响新闻传播？又该如何利用大数据使传播效果最大化？今天，我们请环球时报舆情中心副主任戴元...
Does Foreign Key improve query performance?
...the foreign key relationship already inforces that for you.
So this:
select p.ProductId, p.Name, c.CategoryId, c.Name AS Category
from Products p inner join ProductCategories c on p.CategoryId = c.CategoryIdwhere c.CategoryId = 1;
Becomes this:
SELECT p.ProductId, p.Name, c.CategoryId, c.N...
LinkedIn联合创始人：初创企业早期别花钱买用户 - 资讯 - 清泛网 - 专注C/C...
...流行。
Allen以LinkedIn的发展为例，分享了LinkedIn起步阶段如何在资金有限的情况下实现用户爆发式增长的。他表示在初创期企业每个员工都是“增长黑客”，LinkedIn当时最看重的是员工做事的速度和尝试项目的多样性；此外，Linke...
如何高效的学习掌握新技术 - 杂谈 - 清泛网 - 专注C/C++及内核技术
如何高效的学习掌握新技术最近一段时间，把React学习实践了一把，算是又多掌握了一门新技术，虽然学习过程比较辛苦曲折，但熟练掌握后感觉还是很好的，以后又多了一...最近一段时间，把React学习实践了一把，算是又多掌...
Installing specific package versions with pip
I'm trying to install version 1.2.2 of the MySQL_python adaptor, using a fresh virtualenv created with the --no-site-packages option. The current version shown in PyPi is 1.2.3 . Is there a way to install the older version? I found an article stating that this should do it:
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Is the primary key automatically indexed in MySQL?
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According to http://dev.mysql.com/doc/refman/5.0/en/constraint-primary-key.html it would appear that this is would be implicit
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Can I mix MySQL APIs in PHP?
I have searched the net and so far what I have seen is that you can use mysql_ and mysqli_ together meaning:
4 Answers
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How to select rows with no matching entry in another table?
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Here's a simple query:
SELECT t1.ID
FROM Table1 t1
LEFT JOIN Table2 t2 ON t1.ID = t2.ID
WHERE t2.ID IS NULL
The key points are:
LEFT JOIN is used; this will return ALL rows from Table1, regardless of whether or not there is a matching row i...
Retrieve the maximum length of a VARCHAR column in SQL Server
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Use the built-in functions for length and max on the description column:
SELECT MAX(LEN(DESC)) FROM table_name;
Note that if your table is very large, there can be performance issues.
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How do I find duplicate values in a table in Oracle?
...then use a HAVING clause to find values that appear greater than one time.
SELECT column_name, COUNT(column_name)
FROM table_name
GROUP BY column_name
HAVING COUNT(column_name) > 1;
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