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What are the differences between virtual memory and physical memory?
...perating system creates and deals with these mappings - utilizing the page table, among other data structures to maintain the mappings. Virtual memory mappings are always found in the page table or some similar data structure (in case of other implementations of virtual memory, we maybe shouldn't ca...
Is there a combination of “LIKE” and “IN” in SQL?
...an use REGEXP_LIKE (available from Oracle version 10 onwards).
An example table:
SQL> create table mytable (something)
2 as
3 select 'blabla' from dual union all
4 select 'notbla' from dual union all
5 select 'ofooof' from dual union all
6 select 'ofofof' from dual union all
7 ...
Can a foreign key be NULL and/or duplicate?
...mply requires that the value in that field must exist first in a different table (the parent table). That is all an FK is by definition. Null by definition is not a value. Null means that we do not yet know what the value is.
Let me give you a real life example. Suppose you have a database that sto...
How to work around the lack of transactions in MongoDB?
...is that, in a relational database, we need to make changes across multiple tables. Usually tables that need to be joined and so we want to do that all at once. And to do it, since there are multiple tables, we'll have to begin a transaction and do all those updates and then end the transaction. But ...
What is a good reason to use SQL views?
...one of the previous answers seem to have mentioned is easier deployment of table structure changes.
Say, you wish to retire a table (T_OLD) containing data for active users, and instead use a new table with similar data (named T_NEW) but one that has data for both active and inactive users, with on...
Oracle: how to UPSERT (update or insert into a table?)
The UPSERT operation either updates or inserts a row in a table, depending if the table already has a row that matches the data:
...
SET versus SELECT when assigning variables?
... @var varchar(20)
set @var = 'Joe'
set @var = (select name from master.sys.tables where name = 'qwerty')
select @var /* @var is now NULL */
set @var = 'Joe'
select @var = name from master.sys.tables where name = 'qwerty'
select @var /* @var is still equal to 'Joe' */
...
Is there an SQLite equivalent to MySQL's DESCRIBE [table]?
...ed learning SQLite . It would be nice to be able to see the details for a table, like MySQL's DESCRIBE [table] . PRAGMA table_info [table] isn't good enough, as it only has basic information (for example, it doesn't show if a column is a field of some sort or not). Does SQLite have a way to do t...
Finding duplicate values in MySQL
I have a table with a varchar column, and I would like to find all the records that have duplicate values in this column. What is the best query I can use to find the duplicates?
...
Saving changes after table edit in SQL Server Management Studio
If I want to save any changes in a table, previously saved in SQL Server Management Studio (no data in table present) I get an error message:
...