大约有 3,620 项符合查询结果（耗时：0.0206秒） [XML]
What is the difference between partitioning and bucketing a table in Hive ?
... querying the data. For example, in the above table, if we write the below sql, it need to scan all the records in the table which reduces the performance and increases the overhead.
select * from sales_table where product_id='P1'
To avoid full table scan and to read only the records related to p...
Simple explanation of MapReduce?
...taset can then be reduced to a scalar value.
So if you think of it like a SQL statement
SELECT SUM(salary)
FROM employees
WHERE salary > 1000
GROUP by deptname
We can use map to get our subset of employees with salary > 1000
which map emits to the barrier into group size buckets.
Reduce ...
Why Qt is misusing model/view terminology?
... model you are using (own model subclass: probably within the model; e.g. QSqlTableModel: outside (but maybe cached within) the model). To put your models and views together, use own classes which then implement the business logic.
Long answer
Qt's model/view approach and terminology:
Qt provid...
What is the difference between JSON and Object Literal Notation?
...tion in the language itself. It is derived from a single language.
SQL Language - Hibernate MySQL Dialect, Oracle Dialect,.. which have some changes or added functionality.
Information about the browser and computer of your users.
navigator.appName // "Netscape"
ECMAScript is the scr...
What column type/length should I use for storing a Bcrypt hashed password in a Database?
...ectively.
As you use the 2a format, you’ll need 60 bytes. And thus for MySQL I’ll recommend to use the CHAR(60) BINARYor BINARY(60) (see The _bin and binary Collations for information about the difference).
CHAR is not binary safe and equality does not depend solely on the byte value but on the ...
REST, HTTP DELETE and parameters
...
It's an old question, but here are some comments...
In SQL, the DELETE command accepts a parameter "CASCADE", which allows you to specify that dependent objects should also be deleted. This is an example of a DELETE parameter that makes sense, but 'man rm' could provide others. H...
Using ThreadPool.QueueUserWorkItem in ASP.NET in a high traffic scenario
...
What about database inserts? Is there an ASYNC SQL command (like Execute)? Database inserts are about the slowest I/O operation around (because of locking) and having the main thread wait for the row(s) to be inserted is just a waste of CPU cycles.
–...
Difference between DateTime and Time in Ruby
...idually. This is a Ruby on Rails construct that serves as a wrapper around SQL-standard DATETIME fields. These contain arbitrary dates and can represent nearly any point in time as the range of expression is typically very large.
DateTime.new
# => Mon, 01 Jan -4712 00:00:00 +0000
So it's reass...
Troubleshooting “Illegal mix of collations” error in mysql
...the below error when trying to do a select through a stored procedure in MySQL.
16 Answers
...
Most useful NLog configurations [closed]
...etLogger("Database.Query");
Logger logger = LogManager.GetLogger("Database.SQL");
Logger logger = LogManager.GetLogger("Analysis.Financial");
Logger logger = LogManager.GetLogger("Analysis.Personnel");
Logger logger = LogManager.GetLogger("Analysis.Inventory");
And so on. With hierarchical logger...