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  • How do I select a random record efficiently in MySQL?

    - by user198729
    mysql> EXPLAIN SELECT * FROM urls ORDER BY RAND() LIMIT 1; +----+-------------+-------+------+---------------+------+---------+------+-------+---------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+-------+---------------------------------+ | 1 | SIMPLE | urls | ALL | NULL | NULL | NULL | NULL | 62228 | Using temporary; Using filesort | +----+-------------+-------+------+---------------+------+---------+------+-------+---------------------------------+ The above doesn't qualify as efficient,how should I do it properly?

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  • Is there a way to listen for changes in an MySQL database table using Java and JDBC?

    - by adrian7
    I have a number of users which are logged in at a time in my desktop application. They are working on the same table (create, read, update, delete data) so I have to update their views, to reflect changes, every few seconds - currently I am thinking to use a different thread to do that. I am using the MySQL database engine. Is there a way, using JDBC, to listen for changes on a specific table in the database and triggering a Java method only when changes are made?

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  • MYSQL trigger to select from and update the same table gives error #1241 - Operand should contain 1 column(s)

    - by Bipin
    when i try to select and update the same table mysql gives error error #1241 - Operand should contain 1 column(s) The trigger is DELIMITER $$ CREATE TRIGGER visitor_validation BEFORE INSERT ON ratingsvisitors FOR EACH ROW BEGIN SET @ifexists = (SELECT * FROM ratingcounttracks WHERE userid=New.vistorid AND likedate=New.likevalidation AND countfor=New.likeordislike); IF (@ifexists = NULL) THEN INSERT INTO ratingcounttracks(userid, likedate, clickcount,countfor) values (New.vistorid, New.likevalidation ,'1',New.likeordislike); ELSE UPDATE ratingcounttracks SET clickcount=clickcount+1 WHERE userid=New.vistorid AND likedate=New.likevalidation AND countfor=New.likeordislike; END IF; END$$

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  • Fill rows down quickly (column or matrix of zeros)

    - by Mark Miller
    I have an extremely basic question, but I have never found the answer by searching the internet. I simply want to create a large column of zeros with Excel. Sometimes I want to create a huge matrix of zeros (maybe 600 rows by 500 columns) and then replace a few zeros with 1's to create a model design matrix. I have always started by creating a column of, for example, 10 zeros, copying and pasting those zeroes, then copying and pasting the resulting column of 20 zeros, etc., until I had the desired number of rows. Then I would copy and paste that column of zeros one at a time over and over until I had the desired number of columns. This procedure is tedious and time-consuming and I know there must be an easier way. Do you know of any other methods?

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  • Sum of distinc rows after a 1-many table join

    - by Lock
    I have 2 tables that I am joining. Table 1 has 1-many relationship with table 2. That is, table 2 can return multiple rows for a single row of table 1. Because of this, the records of table 1 is duplicated for as many rows as are on table 2.. which is expected. Now, I have a sum on one of the columns from table 1, but because of the multiple rows that get returned on the join, the sum is obviously multiplying. Is there a way to get this number back to its original number? I tried dividing by the count of rows from table 2 but this didnt quite give me the expected result. Are there any analytical functions that could do this? I almost want something like "if this row has not yet been counted in the sum, add it to the sum"

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  • ASP.Net (C#) & MSQL -or- PHP & MySQL for Performance?

    - by Mike Curry
    Money, Staff, Skill and preference to open source or commercial is neutral. Lets take the best of the best programmers (for arguments sake) and think about this: What will perform better overall: PHP & MySQL or ASP.Net & Microsoft SQL (I don't want biased answers, just looking for Performance, and Speed).

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  • How do I identify which MySQL slave has responded?

    - by Kynth
    I have a MySql Master server replicating to three Slaves. A legacy website is performing load-balanced Reads from the Slaves. Is there a method of identifying from the website which of the Slaves is serving a Read request? I'd prefer a function that I can use to return a server name or ip address as part of the SELECT, but any reasonable method will do. Thank you in advance.

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  • How to extend a file definition from an existing module in the node?

    - by c33s
    I use an older version of the example42 mysql module, which defines the mysql.conf file but not its content. Mmy goal is to just include the mysql module and add a content definition in the node. class mysql { ... file { "mysql.conf": path => "${mysql::params::configfile}", mode => "${mysql::params::configfile_mode}", owner => "${mysql::params::configfile_owner}", group => "${mysql::params::configfile_group}", ensure => present, require => Package["mysql"], notify => Service["mysql"], } ... } node xyz { include mysql File["mysql.conf"] { content => template("mymodule/mysql.conf.erb")} } The above code produces a "Only subclasses can override parameters" What is the correct way to just add a content definition to an existing file definition?

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  • Merged rows in column, bottom row fixed height

    - by Styxxy
    I've been struggling some time now with a specific problem using Tables in MS Word (2010). I have a table with 2 rows and 2 columns and the last column, the rows are merged. Now it can happen that this last cell will expand, and I would like to have the last row in the first column to be of a fixed height and the first row has to expand. What happens now is that the last row expands and the first row has a "fixed" height. A picture of the behaviour at this moment: And this is how I would like it to behave: I have been looking through all properties and settings, but I don't seem to find any option. Neither can I found anything by searching online (probably not using the exact right keywords). Any help is appreciated.

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