大约有 37,000 项符合查询结果（耗时：0.0232秒） [XML]
How to reshape data from long to wide format
...
Another option if performance is a concern is to use data.table's extension of reshape2's melt & dcast functions
(Reference: Efficient reshaping using data.tables)
library(data.table)
setDT(dat1)
dcast(dat1, name ~ numbers, value.var = "value")
# name 1 ...
How to list the tables in a SQLite database file that was opened with ATTACH?
What SQL can be used to list the tables, and the rows within those tables in an SQLite database file - once I have attached it with the ATTACH command on the SQLite 3 command line tool?
...
What is the advantage to using bloom filters?
...esenting sets, such as
self-balancing binary search trees,
tries, hash tables, or simple arrays
or linked lists of the entries. Most
of these require storing at least the
data items themselves, which can
require anywhere from a small number
of bits, for small integers, to an
arbitrar...
SQL left join vs multiple tables on FROM line?
...
The old syntax, with just listing the tables, and using the WHERE clause to specify the join criteria, is being deprecated in most modern databases.
It's not just for show, the old syntax has the possibility of being ambiguous when you use both INNER and OUTER j...
php is null or empty?
...
As is shown in the following table, empty($foo) is equivalent to $foo==null and is_null($foo) has the same function of $foo===null. The table also shows some tricky values regarding the null comparison. (ϕ denotes an uninitialized variables. )
...
How can I make Bootstrap columns all the same height?
...margin-bottom: -99999px;
padding-bottom: 99999px;
}
Solution 2 using table
Demo
.row {
display: table;
}
[class*="col-"] {
float: none;
display: table-cell;
vertical-align: top;
}
Solution 3 using flex added August 2015. Comments posted before this don't apply to this sol...
Cannot change column used in a foreign key constraint
I got this error when i was trying to alter my table.
3 Answers
3
...
MySQL remove all whitespaces from the entire column
...
To replace all spaces :
UPDATE `table` SET `col_name` = REPLACE(`col_name`, ' ', '')
To remove all tabs characters :
UPDATE `table` SET `col_name` = REPLACE(`col_name`, '\t', '' )
To remove all new line characters :
UPDATE `table` SET `col_name` = REP...
What's the difference between identifying and non-identifying relationships?
...
An identifying relationship is when the existence of a row in a child table depends on a row in a parent table. This may be confusing because it's common practice these days to create a pseudokey for a child table, but not make the foreign key to the parent part of the child's primary key. Fo...
How do I delete from multiple tables using INNER JOIN in SQL server
...
You can take advantage of the "deleted" pseudo table in this example. Something like:
begin transaction;
declare @deletedIds table ( id int );
delete from t1
output deleted.id into @deletedIds
from table1 as t1
inner join table2 as t2
on t2.id = t...