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• ALTER TABLE without locking the table?

  - by Daniel

  When doing an ALTER TABLE statement in MySQL, the whole table is read-locked for the duration of the statement. If it's a big table, that means insert or update statements could be locked for a looooong time. Is there a way to do a "hot alter", like adding a column in such a way that the table is still updatable throughout the process? Mostly I'm interested in a solution for MySQL but I'd be interested in other RDBMS if MySQL can't do it. To clarify, my purpose is simply to avoid downtime when a new feature that requires an extra table column is pushed to production. Any database schema will change over time, that's just a fact of life. I don't see why we should accept that these changes must inevitably result in downtime; that's just weak.

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• Cannot connect to local database.

  - by Smickie

  Hi, I have apache and mysql set up on my local machine (Mac). Whenever I go to any of my local sites I get the "Error establishing a database connection" whenever anything mySql related happens. It was working perfectly yesterday, but when I started my computer today it is not. I can login to mysql on the terminal and that all works fine, I can view database and run queries in the terminal. Look at all my table etc. I've tried restarting apache. Anyone know what's up? This is worrying.

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• Find top "n" nearby coordinates.

  - by John Hamelink

  I have a coordinate. I want to find the top "n" (n being a variable value) nearest coordinates out of several thousand rows stored on a MySQL database. I also want to be able to define maximum and minimum distances between the coordinate in question and the coordinates in the database. How best am I to go about this? Would it be bonkers to use PHP as I understand the syntax much better than MySQL? If I use a MySQL function, how do I move it between databases if I choose to switch servers? How is it stored? Lastly, what is the most efficient method of getting through all these coordinates accurately - the coordinates are all relatively close to one another? Thanks for your time, John.

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• MySqlDataAdapter or MySqlDataReader for bulk transfer?

  - by Jeff Meatball Yang

  I'm using the MySql connector for .NET to copy data from MySql servers to SQL Server 2008. Has anyone experienced better performance using one of the following, versus the other? DataAdapter and calling Fill to a DataTable in chunks of 500 DataReader.Read to a DataTable in a loop of 500 I am then using SqlBulkCopy to load the 500 DataTable rows, then continue looping until the MySql record set is completely transferred. I am primarily concerned with using a reasonable amount of memory and completing in a short amount of time. Any help would be appreciated!

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• [wxWidgets] How to store wxImage into database, using C++?

  - by Thomas Matthews

  I have some wxImages and I would like to store them into a BLOB (Binary Large OBject) field in a MySQL database. There are no methods in wxImage nor wxBitmap for obtaining the binary data as an array of unsigned char so I can load into the database. My current workaround is to write the image to a temporary file, then load the BLOB field directly from the file. Is there a more efficient method to load and store a wxImage object into a MySQL BLOB field? I am using MySql C++ connector 1.05, MS Visual Studio 2008, wxWidgets and C++.

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• I am unable to find login page for phpmyadmin

  - by Awan

  I was using phpmyadmin(in Wamp) without a password for root. I thought to set a password for root and goto Privileges page and set a password for root. Now whenever I go to localhost/phpmyadmin page it gives me the following error. MySQL said: Documentation #1045 - Access denied for user 'root'@'localhost' (using password: NO) phpMyAdmin tried to connect to the MySQL server, and the server rejected the connection. You should check the host, username and password in your configuration and make sure that they correspond to the information given by the administrator of the MySQL server. I don't know that what is the problem. It is not showing me a login type page to enter a username and password. Any idea that what is the problem ? Thanks

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• Why Linq is Faster? [closed]

  - by Mayur

  Please tell me why linq is faster than others.

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• C# LINQ Where Predicate Type Arguments

  - by blu

  I have an XElement with values for mock data. I have an expression to query the xml: Expression<Func<XElement, bool>> simpleXmlFunction = b => int.Parse(b.Element("FooId").Value) == 12; used in: var simpleXml = xml.Elements("Foo").Where(simpleXmlFunction).First(); The design time error is: The type arguments for method 'System.Linq.Enumerable.Where(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly' The delegate supplied to Where should take in an XElement and return a bool, marking if the item matches the query, I am not sure how to add anything more to the delegate or the where clause to mark the type. Also, the parallel method for the real function against the Entity Framework does not have this issue. What is not correct with the LINQ-to-XML version?

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• How to install MySQLdb package? (ImportError: No module named setuptools)

  - by Verrtex

  Hi All, I am trying to install MySQLdb package. I found the source code here. I did the following: gunzip MySQL-python-1.2.3c1.tar.gz tar xvf MySQL-python-1.2.3c1.tar cd MySQL-python-1.2.3c1 python setup.py build As the result I got the following: Traceback (most recent call last): File "setup.py", line 5, in ? from setuptools import setup, Extension ImportError: No module named setuptools Does anybody knows how to solve this problem? By the way, if I am able to do the described step, I will need to do the following: sudo python setup.py install And I have no system-administrator-rights. Do I still have a chance to install MySQLdb? Thank you.

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• How to get date format in result set?

  - by Prasanna

  I have a sql to get data form mysql their I used dateformat to convert date required format Here is the sql SELECT m.id, m.subject, m.body, m.read, m.hide, m.thread_id, DATE_FORMAT(m.sent_date, '%d-%b-%Y') sent_date, u.username to_name FROM messages m, users u WHERE u.school_id = m.school_id AND u.id = m.to_user_id AND m.school_id = 18 AND m.user_id = 53 AND m.status = 'sent' ORDER BY m.sent_date DESC When I run this sql directly in mysql it works fine, sent_date comes as (19-Apr-2010). When I excute this in ruby, in result set the sent_date is stores as (Tue Apr 20 00:00:00 UTC 2010) messages = Message.find_by_sql(sql) puts messages[0]['sent_date'] puts statement prints "Tue Apr 20 00:00:00 UTC 2010" how to get same date format in mysql result and ruby result set. Thanks

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• fuzzy DISTINCT Values

  - by user982853

  I have a database of real estate listings and need to return a list of neighborhoods. Right now I am using mysql DISTINCT which returns all of the distinct values. My probelm is that there is a lot of neighborhoods that have similar names: example: Park View Sub 1 Park View Park View Sub 2 Park View Sub 3 Great Lake Sub 1 Great Lake Sub 2 Great Lake Great Lake Sub 3 I am looking for an easy php or mysql solution that would recognize that "Park View" and "Great Lake" already exists and ONLY return "Park View" and "Great Lake". My initial thought is to some how get the sort order by length so that the short values are at the top and then loop through using strstr. This sound like a large task I am wondering if there is a function either in mysql or php that would easily do this.

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• innodb lock wait timeout

  - by shantanuo

  As per the documentation link given below: When a lock wait timeout occurs, the current statement is not executed. The current transaction is not rolled back. (Until MySQL 5.0.13 InnoDB rolled back the entire transaction if a lock wait timeout happened. You can restore this behavior by starting the server with the --innodb_rollback_on_timeout option, available as of MySQL 5.0.32. http://dev.mysql.com/doc/refman/5.0/en/innodb-parameters.html#sysvar_innodb_lock_wait_timeout Does it mean that when a lock wait timeout occurs, it compromises the transactional integrity? "roollback on timeout" was the default behaviour till 5.0.13 and I guess that was the correct way to handle such situations. Does anyone think that this should be the default behaviour and the user should not be asked to add a parameter for a functionality that is taken for granted?

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• How important is caching for a site's speed with PHP?

  - by benhowdle89

  I've just made a user-content orientated website http://www.humanisms.co.uk Its done in PHP, MySQL and jQuery's AJAX, at the moment there is only a dozen or so submissions and already i can feel it lagging slightly when it goes to a new page (therefore running a new mysql query) Is it most important for me to try and optimise my mysql queries (by prepared statements) or is it worth in looking at CDN's (amazon s3) and caching (much like the WordPress plugin WP Super Cache) which works by serving static HTML files when there hasnt been new content submitted. Which route is the most beneficial, for me as a developer, to take, ie. where am i better off concentrating my efforts to speed up the site?

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• Drive space hungry NoSQL's databases

  - by forum_inquisitor

  I've tested NoSQL databases like CouchDB, MongoDB and Cassandra and observed tendence to absorbing very large amount of drive space relative to inserted key-value pairs. When comparing CouchDB and MySQL schemaless databases CouchDB is consuming much more drive space than MySQL. I know about that key-value DBs by default are versioning and have long uuid and need key optimalisation - the comparison was between about 15 mln rows in MySQL and 1-5 mln documents listed NoSQL DB's. My question is : Is there any NoSQL with good compaction / compression of data? So that I can have NoSQL database with a size closer to 5GB than 50GB?

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• Combining DROP USER and DROP DATABASE with SELECT .. WHERE query?

  - by zsero

  I'd like to make a very simple thing, replicate the functionality of mysql's interactive mysql_secure_installation script. My question is that is there a simple, built-in way in MySQL to combine the output of a SELECT query with the input of a DROP user or DROP database script? For example, if I'd like to drop all users with empty passwords. How could I do that with DROP USER statement? I know an obvious solution would be to run everything for example from a Python script, run a query with mysql -Bse "select..." parse the output with some program construct the drop query run it. Is there an easy way to do it in a simple SQL query? I've seen some example here, but I wouldn't call it simple: http://stackoverflow.com/a/12097567/518169 Would you recommend making a combined query, or just to parse the output using for example Python or bash scripts/sed?

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• Python: mysqldb install error

  - by Grenko

  So i've been pulling my hair out trying to install the mysqldb package. When i run the build i get a long transcript of errors, heres just part of it, i would posit it all but its huge list of errors [rv@med240-183 MySQL-python-1.2.3c1]$ sudo python setup.py build [sudo] password for rv: running build running build_py copying MySQLdb/release.py -> build/lib.linux-i686-2.6/MySQLdb running build_ext building '_mysql' extension gcc -pthread -fno-strict-aliasing -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i586 -mtune=generic -fasynchronous-unwind-tables -D_GNU_SOURCE -fPIC -fPIC -Dversion_info=(1,2,3,'gamma',1) -D__version__=1.2.3c1 -I/usr/include/mysql -I/usr/include/python2.6 -c _mysql.c -o build/temp.linux-i686-2.6/_mysql.o -g -pipe -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -fasynchronous-unwind-tables -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -fno-strict-aliasing -fwrapv -fPIC -DUNIV_LINUX _mysql.c:36:23: error: my_config.h: No such file or directory _mysql.c:38:19: error: mysql.h: No such file or directory Any ideas?

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• In SQL, what does Group By mean without Count(*), or Sum(), Max(), avg(), ..., and what are some use

  - by Jian Lin

  In SQL, if we use Group By without Count(*) or Sum(), etc, then the result is as follows: mysql> select * from sentGifts; +--------+------------+--------+------+---------------------+--------+ | sentID | whenSent | fromID | toID | trytryWhen | giftID | +--------+------------+--------+------+---------------------+--------+ | 1 | 2010-04-24 | 123 | 456 | 2010-04-24 01:52:20 | 100 | | 2 | 2010-04-24 | 123 | 4568 | 2010-04-24 01:56:04 | 100 | | 3 | 2010-04-24 | 123 | NULL | NULL | 1 | | 4 | 2010-04-24 | NULL | 111 | 2010-04-24 03:10:42 | 2 | | 5 | 2010-03-03 | 11 | 22 | 2010-03-03 00:00:00 | 6 | | 6 | 2010-04-24 | 11 | 222 | 2010-04-24 03:54:49 | 6 | | 7 | 2010-04-24 | 1 | 2 | 2010-04-24 03:58:45 | 6 | +--------+------------+--------+------+---------------------+--------+ 7 rows in set (0.00 sec) mysql> select *, count(*) from sentGifts group by whenSent; +--------+------------+--------+------+---------------------+--------+----------+ | sentID | whenSent | fromID | toID | trytryWhen | giftID | count(*) | +--------+------------+--------+------+---------------------+--------+----------+ | 5 | 2010-03-03 | 11 | 22 | 2010-03-03 00:00:00 | 6 | 1 | | 1 | 2010-04-24 | 123 | 456 | 2010-04-24 01:52:20 | 100 | 6 | +--------+------------+--------+------+---------------------+--------+----------+ 2 rows in set (0.00 sec) mysql> select * from sentGifts group by whenSent; +--------+------------+--------+------+---------------------+--------+ | sentID | whenSent | fromID | toID | trytryWhen | giftID | +--------+------------+--------+------+---------------------+--------+ | 5 | 2010-03-03 | 11 | 22 | 2010-03-03 00:00:00 | 6 | | 1 | 2010-04-24 | 123 | 456 | 2010-04-24 01:52:20 | 100 | +--------+------------+--------+------+---------------------+--------+ 2 rows in set (0.00 sec) Only 1 row is returned per "group". What does it mean when there is no "Count(*)", etc when using "Group By", and what are it uses? thanks.

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• setting java classpath for Libre Office Base in Fedora 16

  - by foampile

  using Fedora 16 OS. i want to use Libre Office Base to connect to MySQL. when i set up the JDBC connection, it asks me for the driver, however, it cannot be loaded (because it doesn't see it in the classpath). does anybody know how to set the classpath for Libre Office? is there like a config util tool for that? e.g. my driver is [B]com.mysql.jdbc.Driver [/B]situated in[B] /usr/share/java/mysql-connector-java-5.1.17.jar[/B]. it works fine when i connect from other JDBC clients, like straight Java or Eclipse Quantum plugin. the problem is that Libre Office does not ask me for the (class)path of where it can find the driver and i do not know where and how to set it so that it becomes visible. thanks

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• How to change a primary key in SQL to auto_increment?

  - by Jian Lin

  I have a table in MySQL that has a primary key: mysql> desc gifts; +---------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+-------+ | giftID | int(11) | NO | PRI | NULL | | | name | varchar(80) | YES | | NULL | | | filename | varchar(80) | YES | | NULL | | | effectiveTime | datetime | YES | | NULL | | +---------------+-------------+------+-----+---------+-------+ but I wanted to make it auto_increment. The following statement failed. How can it be modified so that it can work? thanks mysql> alter table gifts modify giftID int primary key auto_increment; ERROR 1068 (42000): Multiple primary key defined

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• Rails: find_by_sql and PREPARE stmt FROM... i cant make it work

  - by Totty

  I have this query and I have an error: images = Image.find_by_sql('PREPARE stmt FROM \' SELECT * FROM images AS i WHERE i.on_id = 1 AND i.on_type = "profile" ORDER BY i.updated_at LIMIT ?, 6\ '; SET @lower_limit := ((5 DIV 6) * 6); EXECUTE stmt USING @lower_limit;') Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SET @lower_limit := ((5 DIV 6) * 6); EXECUTE stmt USING @lower_limit' at line 1: PREPARE stmt FROM ' SELECT * FROM images AS i WHERE i.on_id = 1 AND i.on_type = "profile" ORDER BY i.updated_at LIMIT ?, 6'; SET @lower_limit := ((5 DIV 6) * 6); EXECUTE stmt USING @lower_limit; EDIT: after finding the answer to: http://stackoverflow.com/questions/2566620/mysql-i-need-to-get-the-offset-of-a-item-in-a-query i need another help here to port it to rails.

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• Should I use "id" or "unique username"?

  - by roa3

  I am using PHP, AS3 and mysql. I have a website. A flash(as3) website. The flash website store the members' information in mysql database through php. In "members" table, i have "id" as the primary key and "username" as a unique field. Now my situation is: When flash want to display a member's profile. My questions: Should Flash pass the member "ID" or "username" to php to process the mysql query? Is there any different passing the "id" or "username"? Which one is more secure? Which one you recommend? I would like to optimize my website in terms of security and performance.

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• Any way to avoid a filesort when order by is different to where clause?

  - by Julian

  I have an incredibly simple query (table type InnoDb) and EXPLAIN says that MySQL must do an extra pass to find out how to retrieve the rows in sorted order. SELECT * FROM `comments` WHERE (commentable_id = 1976) ORDER BY created_at desc LIMIT 0, 5 exact explain output: table select_type type extra possible_keys key key length ref rows comments simple ref using where; using filesort common_lookups common_lookups 5 const 89 commentable_id is indexed. Comments has nothing trick in it, just a content field. The manual suggests that if the order by is different to the where, there is no way filesort can be avoided. http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html I also tried order by id as well as it's equivalent but makes no difference, even if I add id as an index (which I understand is not required as id is indexed implicitly in MySQL). thanks in advance for any ideas!

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• Best way to migrate servers without losing any data and with no downtime(?)

  - by ina

  This is a methodology question from a freelancer, with a corollary on MySQL.. Is there a way to migrate from an old dedicated server to a new one without losing any data in-between - and with no downtime? In the past, I've had to lose MySQL data between the time when the new server goes up (i.e., all files transferred, system up and ready), and when I take the old server down (data still transferred to old until new one takes over). There is also a short period where both are down for DNS, etc., to refresh. Is there a way for MySQL/root to easily transfer all data that was updated/inserted between a certain time frame?

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• How to inherit from the main class in java

  - by user225269

  I have two java classes. One is NewFrame.java where the forms(buttons, textfields) are located. And the other one is Main.java where I have put the connection string for mysql: Main.java looks like this: public class Main { /** * @param args the command line arguments */ public static void main(String[] args) throws Exception { // TODO code application logic here Class.forName("com.mysql.jdbc.Driver"); Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/employee_record", "root", "password"); PreparedStatement statement = con.prepareStatement("select * from employee"); ResultSet result = statement.executeQuery(); } } How do I inherit from the main.java so that the declarations in it would be universally accessible to the forms in NewFrame.java? Please help. Thanks

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• Please help me understand this PHP script.Noob here

  - by NissGTR

  I'm learning PHP,MySQL and came across this function today function get_director($director_id) { global $db; $query = 'SELECT people_fullname FROM people WHERE people_id = ' . $director_id; $result = mysql_query($query, $db) or die(mysql_error($db)); $row = mysql_fetch_assoc($result); extract($row); return $people_fullname; } I understand what functions are and I've created a few while learning PHP.But this one is a bit more complicated.I can't understand the WHERE people_id = ' . $director_id I'm new to MySQL.I guess the single quote ends the MySQL statement?And then it is concatenated with the argument? Please help me out.

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