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Understanding garbage collection in .NET
...ow. The second duty is however completely invisible. It also generates a table that describes how the local variables inside the method body are used. That table has an entry for each method argument and local variable with two addresses. The address where the variable will first store an object ...
What is the reason not to use select *?
...nt, the SQL execution engine will error if that column is removed from the table and the query is executed.
You can more easily scan code where that column is being used.
You should always write queries to bring back the least amount of information.
As others mention if you use ordinal column access...
Using backticks around field names
...r field` , `field,with,comma`
Which does of course generate badly named tables.
If you're just being concise I don't see a problem with it,
you'll note if you run your query as such
EXPLAIN EXTENDED Select foo,bar,baz
The generated warning that comes back will have back-ticks and fully qua...
Count number of rows within each group
...
An old question without a data.table solution. So here goes...
Using .N
library(data.table)
DT <- data.table(df)
DT[, .N, by = list(year, month)]
share
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...
How can I rename a field for all documents in MongoDB?
...
For some reason, this didn't work for me when I used the "table.field" : "table.field" syntax. It did work when I just used the "field" : "field" syntax.
– Ben
Sep 2 '15 at 0:21
...
Is there a way to get a collection of all the Models in your Rails app?
...
ActiveRecord::Base.connection.tables.map do |model|
model.capitalize.singularize.camelize
end
will return
["Article", "MenuItem", "Post", "ZebraStripePerson"]
Additional information If you want to call a method on the object name without model:stri...
How to move a model between two Django apps (Django 1.7)
...on(migrations.Migration):
database_operations = [migrations.AlterModelTable('TheModel', 'newapp_themodel')]
state_operations = [migrations.DeleteModel('TheModel')]
operations = [
migrations.SeparateDatabaseAndState(
database_operations=database_operations,
state_...
Finding duplicate values in a SQL table
...till requires all non-aggregated columns in the GROUP BY.
MySQL is unpredictable and you need sql_mode=only_full_group_by:
GROUP BY lname ORDER BY showing wrong results;
Which is the least expensive aggregate function in the absence of ANY() (see comments in accepted answer).
Oracle isn't mainstr...
How to drop columns using Rails migration
What's the syntax for dropping a database table column through a Rails migration?
20 Answers
...
Why do I get a “Null value was assigned to a property of primitive type setter of” error message whe
...he solution is replace primitive type with primitive wrapper class in your tableName.java file.
Such as:
@Column(nullable=true, name="client_os_id")
private Integer client_os_id;
public int getClient_os_id() {
return client_os_id;
}
public void setClient_os_id(int clientOsId) {
client_os_...