大约有 47,000 项符合查询结果（耗时：0.0319秒） [XML]
How does one reorder columns in a data frame?
...
You can also use the subset function:
data <- subset(data, select=c(3,2,1))
You should better use the [] operator as in the other answers, but it may be useful to know that you can do a subset and a column reorder operation in a single command.
Update:
You can also use the select...
Group by in LINQ
... p in persons
group p.car by p.PersonId into g
select new { PersonId = g.Key, Cars = g.ToList() };
Or as a non-query expression:
var results = persons.GroupBy(
p => p.PersonId,
p => p.car,
(key, g) => new { PersonId = key, Cars = g.ToList() });
...
How do I reset a sequence in Oracle?
...q_name in varchar2 )
is
l_val number;
begin
execute immediate
'select ' || p_seq_name || '.nextval from dual' INTO l_val;
execute immediate
'alter sequence ' || p_seq_name || ' increment by -' || l_val ||
' minvalue 0';
...
Best way to test SQL queries [closed]
...value, and all values are consecutive:
create view cm_absolute_month as
select *, year * 12 + month as absolute_month from month_value;
Now what we have to test is inherent in our spec, namely that for any tuple (year, month), there is one and only one (absolute_month), and that (absolute_month...
Search text in stored procedure in SQL Server
...t the schema name by adding SCHEMA_NAME(o.schema_id) AS Schema_Name to the select clause.
– patricus
Jul 7 '16 at 15:07
6
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Get list of all tables in Oracle?
...
SELECT owner, table_name
FROM dba_tables
This is assuming that you have access to the DBA_TABLES data dictionary view. If you do not have those privileges but need them, you can request that the DBA explicitly grants you...
How to get the connection String from a database
... Visual Studio go to Tools -> Connect to Database.
2] Under Server Name Select your Database Server Name (Let the list Populate if its taking time).
3] Under Connect to a Database, Select Select or enter a database name.
4] Select your Database from Dropdown.
5] After selecting Database try Test ...
What does it mean when a CSS rule is grayed out in Chrome's element inspector?
... because one or more rules from the set are being applied to the currently selected DOM node.
I guess, for the sake of completeness, dev tools shows all the rules from that set, whether they are applied or not.
In the case where a rule is applied to the currently selected element due to inheritance...
CROSS JOIN vs INNER JOIN in SQL
...ame situation.
These 2 examples will return the same result:
Cross join
select * from table1 cross join table2 where table1.id = table2.fk_id
Inner join
select * from table1 join table2 on table1.id = table2.fk_id
Use the last method
...
Database Design for Tagging
... to rebuilt every time a question has a tag added or removed. A query like select * from question q inner join question_has_tag qt where tag_id in (select tag_id from tags where (what we want) minus select tag_id from tags where (what we don't) should be fine and scale out assuming the right b-tree ...