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Subset of rows containing NA (missing) values in a chosen column of a data frame
...t "NA" strings to NA values, and let "NULL" strings as is).
If using read.table() or read.csv(), you should consider the "na.strings" argument to do clean data import, and always work with real R NA values.
An example, working in both cases "NULL" and "NA" cells :
DF <- read.csv("file.csv", na...
The case against checked exceptions
...with it.
This would be clearer with a counter-case. Imagine I'm writing a table API. I have the table model somewhere with an API including this method:
public RowData getRowData(int row)
Now as an API programmer I know there will be cases where some client passes in a negative value for the ro...
How do I make text bold in HTML?
... it within your CSS ("legend {font-weight: bold;}").
Want to distinguish a table caption from the table it captions? Use a "caption" element and suggest a bold style for it within your CSS ("caption {font-weight: bold;}").
Want to distinguish table headings from table data cells? Use a "th" element ...
How do you manually execute SQL commands in Ruby On Rails using NuoDB
...n.execute("foo")
with "foo" being the sql statement( i.e. "SELECT * FROM table").
This command will return a set of values as a hash and put them into the results variable.
So on my rails application_controller.rb I added this:
def execute_statement(sql)
results = ActiveRecord::Base.connectio...
Is it a good idea to index datetime field in mysql?
.... In my application I will have many rows for example I currently have one table with 4 million records. Most of my queries use datetime clause to select data. Is it a good idea to index datetime fields in mysql database?
...
SQL - Select first 10 rows only?
...
In SQL server, use:
select top 10 ...
e.g.
select top 100 * from myTable
select top 100 colA, colB from myTable
In MySQL, use:
select ... order by num desc limit 10
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...temap/0.9/sitemap.xsd\">\n";
$querys = DB::query("SELECT a.tid FROM ".DB::table('forum_thread')." a inner join ".DB::table('forum_forum')." b on a.fid=b.fid ORDER BY a.tid DESC LIMIT 0,10000");
while($threadfid = DB::fetch($querys))
{
$turl=$web_root.'thread-'.$threadfid['tid'].'-1-1.html';//注...
Rails new vs create
...fferently.
An HTTP GET to /resources/new is intended to render a form suitable for creating a new resource, which it does by calling the new action within the controller, which creates a new unsaved record and renders the form.
An HTTP POST to /resources takes the record created as part of the ne...
Select something that has more/less than x character
...L Server, Use the LEN (Length) function:
SELECT EmployeeName FROM EmployeeTable WHERE LEN(EmployeeName) > 4
MSDN for it states:
Returns the number of characters of the specified string expression,
excluding trailing blanks.
Here's the link to the MSDN
For oracle/plsql you can use Leng...
How to reset or change the MySQL root password?
...init.d/mysql stop
Start the mysqld configuration: sudo mysqld --skip-grant-tables &
In some cases, you've to create the /var/run/mysqld first:
sudo mkdir -v /var/run/mysqld && sudo chown mysql /var/run/mysqld
Run: sudo service mysql start
Login to MySQL as root: mysql -u root mysql
Re...