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Two single-column indexes vs one two-column index in MySQL?
...a single composite index can speed up several kinds of queries on the same table." - Multiple-Column Indexes
– AlikElzin-kilaka
Sep 9 '18 at 4:46
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MySQL order by before group by
...hor is to use a subquery to return the max date and then join that to your table on both the post_author and the max date.
The solution should be:
SELECT p1.*
FROM wp_posts p1
INNER JOIN
(
SELECT max(post_date) MaxPostDate, post_author
FROM wp_posts
WHERE post_status='publish'
...
What is a columnar database?
...are build upon traditional, row-oriented, DBMS, simply storing the info in tables with one (or rather often two) columns (and adding the necessary layer to access the columnar data in an easy fashion).
How do they differ from relational databases?
They generally differ from traditional (row-oriente...
UITableView is starting with an offset in iOS 7
I have dragged a plain jane UITableView onto a UIViewController in iOS 7.
20 Answers
2...
How to use count and group by at the same select statement
...atement.
Is there a way for this directly from sql?
For example, having a table with users I want to select the different towns and the total number of users
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Why is XOR the default way to combine hashes?
... uniform probability distributions.
This can be seen by writing out truth tables:
a | b | a AND b
---+---+--------
0 | 0 | 0
0 | 1 | 0
1 | 0 | 0
1 | 1 | 1
a | b | a OR b
---+---+--------
0 | 0 | 0
0 | 1 | 1
1 | 0 | 1
1 | 1 | 1
a | b | a XOR b
---+---+--------
...
UITableView - change section header color
How can I change color of a section header in UITableView?
31 Answers
31
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log4j logging hierarchy order
...
This table might be helpful for you:
Going down the first column, you will see how the log works in each level. i.e for WARN, (FATAL, ERROR and WARN) will be visible. For OFF, nothing will be visible.
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What is an ORM, how does it work, and how should I use one? [closed]
...(book);
}
With an ORM library, it would look like this:
book_list = BookTable.query(author="Linus");
The mechanical part is taken care of automatically via the ORM library.
Pros and Cons
Using ORM saves a lot of time because:
DRY: You write your data model in only one place, and it's easier...
Rake just one migration
...
To expand on what Ryan says, if the table has been dropped from the database outside of Rails, rake db:migrate:up VERSION=my_version may do nothing, because the schema_migrations table still says it is has been run. In the same situation rake db:migrate:redo VE...