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What is SELF JOIN and when would you use it? [duplicate]
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You use a self join when a table references data in itself.
E.g., an Employee table may have a SupervisorID column that points to the employee that is the boss of the current employee.
To query the data and get information for both people in one row,...
Search for all occurrences of a string in a mysql database [duplicate]
...how to locate all occurrences of a url in a database. I want to search all tables and all fields. But I have no idea where to start or if it's even possible.
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Fast way of counting non-zero bits in positive integer
...se that.
To answer a question in the comments, for bytes I'd use a lookup table. You can generate it at runtime:
counts = bytes(bin(x).count("1") for x in range(256)) # py2: use bytearray
Or just define it literally:
counts = (b'\x00\x01\x01\x02\x01\x02\x02\x03\x01\x02\x02\x03\x02\x03\x03\x04'...
PostgreSQL naming conventions
Where can I find a detailed manual about PostgreSQL naming conventions? (table names vs. camel case, sequences, primary keys, constraints, indexes, etc...)
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mysql -> insert into tbl (select from another table) and some default values [duplicate]
As the title says, I am trying to insert into one table selecting values from another table and some default values.
5 Ans...
How can I list all collections in the MongoDB shell?
...e current database that I'm using?
Three methods
show collections
show tables
db.getCollectionNames()
To list all databases:
show dbs
To enter or use a given database:
use databasename
To list all collections:
show collections
Output:
collection1
collection2
system.indexes
(o...
MySQL high CPU usage [closed]
... time, and use that to make sure you don't have any queries locking up key tables for too long.
Some other things you can check would be to run the following query while the CPU load is high:
SHOW PROCESSLIST;
This will show you any queries that are currently running or in the queue to run, what...
INSERT IF NOT EXISTS ELSE UPDATE?
...ot in the insert list will be set to NULL if the row already exists in the table. This is why there's a subselect for the ID column: In the replacement case the statement would set it to NULL and then a fresh ID would be allocated.
This approach can also be used if you want to leave particular fiel...
How do I create a PDO parameterized query with a LIKE statement?
...t out right after I posted:
$query = $database->prepare('SELECT * FROM table WHERE column LIKE ?');
$query->execute(array('value%'));
while ($results = $query->fetch())
{
echo $results['column'];
}
share
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Efficient Algorithm for Bit Reversal (from MSB->LSB to LSB->MSB) in C
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NOTE: All algorithms below are in C, but should be portable to your language of choice (just don't look at me when they're not as fast :)
Options
Low Memory (32-bit int, 32-bit machine)(from here):
unsigned int
reverse(register unsigned int x)
{
x = (((x & 0xaaaaaaaa)...