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What are DDL and DML?
... the database.
CREATE – to create database and its objects like (table, index, views, store procedure, function and triggers)
ALTER – alters the structure of the existing database
DROP – delete objects from the database
TRUNCATE – remove all records from a table, including all ...
Django ManyToMany filter()
...
another way to do this is by going through the intermediate table. I'd express this within the Django ORM like this:
UserZone = User.zones.through
# for a single zone
users_in_zone = User.objects.filter(
id__in=UserZone.objects.filter(zone=zone1).values('user'))
# for multiple zo...
Recommended SQL database design for tags or tagging [closed]
I've heard of a few ways to implement tagging; using a mapping table between TagID and ItemID (makes sense to me, but does it scale?), adding a fixed number of possible TagID columns to ItemID (seems like a bad idea), Keeping tags in a text column that's comma separated (sounds crazy but could work)...
Programmatically creating Markdown tables in R with KnitR
...ver, one thing that I'm not seeing is an easy way to print data frames and tables using Markdown formatting (sort of like xtable , but with Markdown instead of LaTeX or HTML). I know that I can just embed the HTML output from xtable, but I was wondering if there were any Markdown-based solutions?
...
When increasing the size of VARCHAR column on a large table could there be any problems?
...er 2008 and I need to make a VARCHAR field bigger, from (200 to 1200) on a table with about 500k rows. What I need to know is if there are any issues I have not considered.
...
PHP: Storing 'objects' inside the $_SESSION
... it on every request. Then the server uses that ID as a key into a big hashtable of Session objects. Whenever the server gets a request, it looks up the Session info out of its hashtable of session objects based on the ID the client submitted with the request. All this extra work is a double whammy ...
T-SQL: Using a CASE in an UPDATE statement to update certain columns depending on a condition
...tructure of your query, just the data involved. You could do this:
update table set
columnx = (case when condition then 25 else columnx end),
columny = (case when condition then columny else 25 end)
This is semantically the same, but just bear in mind that both columns will always be upda...
Is SQL syntax case sensitive?
...OM, WHERE, etc), but are often written in all caps. However in some setups table and column names are case-sensitive. MySQL has a configuration option to enable/disable it. Usually case-sensitive table and column names are the default on Linux MySQL and case-insensitive used to be the default on Win...
How to edit data in result grid in SQL Server Management Studio
...et a query output in the result grid.
Its true that we can right click the table and say open table to get an editable table output, but what I want is editable query output, only certain rows matching for my criteria, and edit them in the result grid.
...
ROW_NUMBER() in MySQL
... kind of isn't).
I often plump for a null-self-join:
SELECT t0.col3
FROM table AS t0
LEFT JOIN table AS t1 ON t0.col1=t1.col1 AND t0.col2=t1.col2 AND t1.col3>t0.col3
WHERE t1.col1 IS NULL;
“Get the rows in the table for which no other row with matching col1,col2 has a higher col3.” (You w...