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How to set a Django model field's default value to a function call / callable (e.g., a date relative
...ow_add=True in the constructor, the datetime referenced by my_date is "immutable" (only set once when the row is inserted to the table).
With auto_now=True, however, the datetime value will be updated every time the object is saved.
This was definitely a gotcha for me at one point. For reference, ...
Possibility of duplicate Mongo ObjectId's being generated in two different collections?
...of different "types" in the same collection, so why not just put your two "tables" in the same collection. They would share the same _id space, and thus, would be guaranteed unique. Switching from "prospective" to "registered" would be a simple flipping of a field...
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Permanently Set Postgresql Schema Path
... set schema path in Postgres so that I don't every time specify schema dot table e.g. schema2.table .
Set schema path:
3 ...
Optimal way to concatenate/aggregate strings
...r,
COUNT(*) OVER (PARTITION BY ID) AS NameCount
FROM dbo.SourceTable
),
Concatenated AS
(
SELECT
ID,
CAST(Name AS nvarchar) AS FullName,
Name,
NameNumber,
NameCount
FROM Partitioned
WHERE NameNumber = 1
UNION ALL
SELECT...
How to declare an array in Python?
... while some extra space
insert operation is expensive
Check this awesome table of operations complexity.
Also, please see this picture, where I've tried to show most important differences between array, array of references and linked list:
...
Group query results by month and year in postgresql
I have the following database table on a Postgres server:
7 Answers
7
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Add a reference column migration in Rails 4
A user has many uploads. I want to add a column to the uploads table that references the user . What should the migration look like?
...
Transpose a data frame
...
You can use the transpose function from the data.table library. Simple and fast solution that keeps numeric values as numeric.
library(data.table)
# get data
data("mtcars")
# transpose
t_mtcars <- transpose(mtcars)
# get row and colnames in order
colnames(t_mtc...
How to use Servlets and Ajax?
...gt; as JSON
Here's an example which displays List<Product> in a <table> where the Product class has the properties Long id, String name and BigDecimal price. The servlet:
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, I...
MySQL - SELECT WHERE field IN (subquery) - Extremely slow why?
...
Rewrite the query into this
SELECT st1.*, st2.relevant_field FROM sometable st1
INNER JOIN sometable st2 ON (st1.relevant_field = st2.relevant_field)
GROUP BY st1.id /* list a unique sometable field here*/
HAVING COUNT(*) > 1
I think st2.relevant_field must be in the select, because other...