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Difference between Destroy and Delete
...sted). Returns the frozen instance.
The row is simply removed with an SQL DELETE statement on the record's primary key, and no callbacks are executed.
To enforce the object's before_destroy and after_destroy callbacks or any :dependent association options, use #destroy.
ActiveRecord::Pers...
Give examples of functions which demonstrate covariance and contravariance in the cases of both over
...mparator<java.util.Date> { ... } and you want to sort a List<java.sql.Date> with that comparator (java.sql.Date is a sub-class of java.util.Date), you can do with:
<T> void sort(List<T> what, Comparator<? super T> how)
but not with
<T> void sort(List<T>...
SQLite in Android How to update a specific row
...the line should be: myDB.update(TableName, cv, "_id=?", new String[]{id}). SQLite will automatically fill the fourth param into the "?" in the third param, i.e. the WHERE clause. If your third param contains n "?"s , the fourth param should be a String[] of length n
– Cristiano...
Storing DateTime (UTC) vs. storing DateTimeOffset
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Select data from date range between two dates
...ously, second way is much more simple (only two cases against four).
Your SQL will look like:
SELECT * FROM Product_sales
WHERE NOT (From_date > @RangeTill OR To_date < @RangeFrom)
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Deleting all records in a database table
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If you are looking for a way to it without SQL you should be able to use delete_all.
Post.delete_all
or with a criteria
Post.delete_all "person_id = 5 AND (category = 'Something' OR category = 'Else')"
See here for more information.
The records are deleted wit...
How to 'bulk update' with Django?
I'd like to update a table with Django - something like this in raw SQL:
5 Answers
5
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What's the best way of structuring data on firebase?
...There is now a doc on structuring data. Also, see this excellent post on NoSQL data structures.
The main issue with hierarchical data, as opposed to RDBMS, is that it's tempting to nest data because we can. Generally, you want to normalize data to some extent (just as you would do with SQL) despite...
How do you find the row count for all your tables in Postgres
...tatement like the one you used against each table. This is because PostgreSQL keeps row visibility information in the row itself, not anywhere else, so any accurate count can only be relative to some transaction. You're getting a count of what that transaction sees at the point in time when it exe...
Error Code: 2013. Lost connection to MySQL server during query
I got the Error Code: 2013. Lost connection to MySQL server during query error when I tried to add an index to a table using MySQL Workbench.
I noticed also that it appears whenever I run long query.
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