大约有 47,000 项符合查询结果（耗时：0.0565秒） [XML]
Oracle “(+)” Operator
...dize OUTER joins.
The query would be re-written in ANSI-92 syntax as:
SELECT ...
FROM a
LEFT JOIN b ON b.id = a.id
This link is pretty good at explaining the difference between JOINs.
It should also be noted that even though the (+) works, Oracle recommends not using it:
Oracle re...
Oracle “Partition By” Keyword
...d then use that in a calculation against this records salary without a sub select, which is much faster.
Read the linked AskTom article for further details.
share
|
improve this answer
|
...
Only read selected columns
...from the data.table-package:
You can specify the desired columns with the select parameter from fread from the data.table package. You can specify the columns with a vector of column names or column numbers.
For the example dataset:
library(data.table)
dat <- fread("data.txt", select = c("Year...
Measure the time it takes to execute a t-sql query
... to just grab the current date and time.
In SQL Server Management Studio
SELECT GETDATE();
SELECT /* query one */ 1 ;
SELECT GETDATE();
SELECT /* query two */ 2 ;
SELECT GETDATE();
To calculate elapsed times, you could grab those date values into variables, and use the DATEDIFF function:
DECL...
How do I find duplicates across multiple columns?
...
Duplicated id for pairs name and city:
select s.id, t.*
from [stuff] s
join (
select name, city, count(*) as qty
from [stuff]
group by name, city
having count(*) > 1
) t on s.name = t.name and s.city = t.city
...
Rails ActiveRecord date between
...ne day. The field is part of the standard timestamps, is created_at . The selected date is coming from a date_select .
11...
Select 50 items from list at random to write to file
... leaving the original population unchanged. The resulting list is
in selection order so that all sub-slices will also be valid random
samples. This allows raffle winners (the sample) to be partitioned
into grand prize and second place winners (the subslices).
Members of the popul...
Check if a Postgres JSON array contains a string
...
As of PostgreSQL 9.4, you can use the ? operator:
select info->>'name' from rabbits where (info->'food')::jsonb ? 'carrots';
You can even index the ? query on the "food" key if you switch to the jsonb type instead:
alter table rabbits alter info type jsonb using ...
Check if table exists and if it doesn't exist, create it in SQL Server 2008
...
Something like this
IF NOT EXISTS (SELECT * FROM sys.objects
WHERE object_id = OBJECT_ID(N'[dbo].[YourTable]') AND type in (N'U'))
BEGIN
CREATE TABLE [dbo].[YourTable](
....
....
....
)
END
...
How to generate Class Diagram (UML) on Android Studio (IntelliJ Idea)
...ight click on the folder containing the classes you want to visualize, and select Add to simpleUML Diagram.
That's it; you have you fancy class diagram generated from your code!
share
|
improve thi...