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How to rollback a specific migration?
... probably true only for databases which doesn't support Transactional DDL. MySQL doesn't support Transactional DDL: dev.mysql.com/doc/refman/5.0/en/cannot-roll-back.html PostreSQL does: wiki.postgresql.org/wiki/… So if your migration on MySQL database is broken then you have manually to delete pa...
How do you set a default value for a MySQL Datetime column?
...test (str) values ("demo");
Query OK, 1 row affected (0.00 sec)
mysql> select * from test;
+------+---------------------+
| str | ts |
+------+---------------------+
| demo | 2008-10-03 22:59:52 |
+------+---------------------+
1 row in set (0.00 sec)
mysql>
**CAVEAT: IF...
GetProperties() to return all properties for an interface inheritance hierarchy
...(new Type[] { type })
.Concat(type.GetInterfaces())
.SelectMany(i => i.GetProperties());
}
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What's the Linq to SQL equivalent to TOP or LIMIT/OFFSET?
...
In VB:
from m in MyTable
take 10
select m.Foo
This assumes that MyTable implements IQueryable. You may have to access that through a DataContext or some other provider.
It also assumes that Foo is a column in MyTable that gets mapped to a property name.
...
If table exists drop table then create it, if it does not exist just create it
...up the old table,
obviously.
Wrapping all statements with something like SELECT GET_LOCK('__upgrade', -1); ... DO RELEASE_LOCK('__upgrade'); allows to just invoke all statements sequentially without error checking, but I don't think it's a good idea: complexity increases and locking functions in M...
MySQL load NULL values from CSV data
...can see empty strings '' when they download a csv (using IFNULL(Col,'') in SELECT INTO OUTFILE query) for excel but then uploads accept them as null vs having to deal with \N in the csv. Thanks!
– chrisan
Sep 29 '13 at 15:47
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MySQL COUNT DISTINCT
...
Select
Count(Distinct user_id) As countUsers
, Count(site_id) As countVisits
, site_id As site
From cp_visits
Where ts >= DATE_SUB(NOW(), INTERVAL 1 DAY)
Group By site_id
...
Explicit vs implicit SQL joins
...e joined and how they are joined. Try compare larger SQL queries where you selecting from 8 different tables and you have lots of filtering in the where. By using join syntax you separate out the parts where the tables are joined, to the part where you are filtering the rows.
...
Windows、Linux开放指定端口 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...口默认是被防火墙拦截禁止外部访问的。本文简要介绍了如何在不关闭防火墙的情况下开放指定端口。Windows篇：
以下步骤中未提供截图的按照默认设置即可：
设置后立即生效。
Linux篇：
vi /etc/sysconfig/iptables
添...
Clear MySQL query cache without restarting server
...not clear it for me. Also, MySQL server restart does not help. An explicit SELECT SQL_NO_CACHE does the trick, but not RESET QUERY CACHE. sync && echo 3 | sudo tee /proc/sys/vm/drop_caches from the other answer didn't help, too.
– Jānis Elmeris
Aug 24 ...