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SQL Server indexes - ascending or descending, what difference does it make?
...TE INDEX ix_index ON mytable (col1, col2 DESC);
can be used for either:
SELECT *
FROM mytable
ORDER BY
col1, col2 DESC
or:
SELECT *
FROM mytable
ORDER BY
col1 DESC, col2
, but not for:
SELECT *
FROM mytable
ORDER BY
col1, col2
An index on a single colum...
java.net.UnknownHostException: Invalid hostname for server: local
...hostname "localhost" instead, or perhaps 127.0.0.1 or ::1 (the last one is IPv6).
From the javadocs:
Thrown to indicate that the IP address
of a host could not be determined.
127.0.0.1or ::1 or "localhost" should always be the loopback interface, so if that doesn't work I'd be really surpri...
MySQL show current connection info
...e are MYSQL functions you can use. Like this one that resolves the user:
SELECT USER();
This will return something like root@localhost so you get the host and the user.
To get the current database run this statement:
SELECT DATABASE();
Other useful functions can be found here: http://dev.mys...
How to export data as CSV format from SQL Server using sqlcmd?
...
You can run something like this:
sqlcmd -S MyServer -d myDB -E -Q "select col1, col2, col3 from SomeTable"
-o "MyData.csv" -h-1 -s"," -w 700
-h-1 removes column name headers from the result
-s"," sets the column seperator to ,
-w 700 sets the row width to 700 chars (this will nee...
How to use NULL or empty string in SQL
...
Select *
From Table
Where (col is null or col = '')
Or
Select *
From Table
Where IsNull(col, '') = ''
share
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improve t...
实战低成本服务器搭建千万级数据采集系统 - 更多技术 - 清泛网 - 专注C/C++...
...过各大微博的搜索api。就比如新浪微博API针对一个服务器IP的请求次数，普通权限限制是一个小时1w次，最高权限合作授权一个小时4w次。使用应用时还需要有足够的用户，单用户每个应用每小时访问1000次，最高权限4w次需要40个...
Convert data.frame column format from character to factor
...yr::mutate_if() to convert all character columns or dplyr::mutate_at() for select named character columns to factors:
library(dplyr)
# all character columns to factor:
df <- mutate_if(df, is.character, as.factor)
# select character columns 'char1', 'char2', etc. to factor:
df <- mutate_at(d...
How to color System.out.println output? [duplicate]
...7 | white |
| 39 | 49 | default |
+~~~~~~+~~~~~~+~~~~~~~~~~~+
Select Graphic Rendition (SGR)
SGR just allows you to change the text. Many of these do not work in certain terminals, so use these sparingly in production-level projects. However, they can be useful for making program outpu...
difference between socket programming and Http programming
...sponse.
Stream receiveStream = response.GetResponseStream ();
// Pipes the stream to a higher level stream reader with the required encoding format.
StreamReader readStream = new StreamReader (receiveStream, Encoding.UTF8);
Console.WriteLine ("Response stream received.");
Cons...
Modify table: How to change 'Allow Nulls' attribute from not null to allow null
...
I wrote this so I could edit all tables and columns to null at once:
select
case
when sc.max_length = '-1' and st.name in ('char','decimal','nvarchar','varchar')
then
'alter table [' + so.name + '] alter column [' + sc.name + '] ' + st.name + '(MAX) NULL'
when st.name in ('char','decimal','n...