I have developers come to me occasionally mystified by this error messages like this: ERROR 1055 (42000): ‘<tablename>.<columnname>’ isn’t in GROUP BY What does that mean, exactly, and why is the query getting kicked back? To illustrate, let’s say we have a tabe, geodata, which has this data for all US cities–the table has just ..
Executive Summary Advice is seldom welcome. And those who want it most always like it the least. Philip Dormer Stanhope, Earl of Chesterfield (1694-1773) Guiding philosophy of this document: The hero isn’t the developer that battles problems through the weekend, but the one that avoided the problem. Best practices (BP in this document) ..
The Linux kernel provides a tweakable setting that controls how often the swap file is used, called swappiness. A swappiness setting of zero means that the disk will be avoided unless absolutely necessary (you run out of memory), while a swappiness setting of 100 means that programs will be swapped to disk almost instantly. Ubuntu ..
MySQL is SO irritating in its timestamp limitations, in that you can only have one default timestamp column. (Update 6/12/2013: in version 5.6.x, this restriction will be lifted, so I hear) However, you *can* trick MySQL like this. You can use only one of the definitions in one table. Create both timestamp columns like so: ..
CONVERT ALL THE THINGS. Well, almost all the things. #!/bin/bash for database in aaaaa bbbbb ccccc ddddd eeee do thesetables=`mysql -N -B -e “SELECT CONCAT(TABLE_SCHEMA,’.’,TABLE_NAME) \ FROM information_schema.TABLES where TABLE_SCHEMA = \”$database\”” \ AND TABLE_SCHEMA NOT IN (‘mysql’,’information_schema’,’performance_schema’)` alltables=`echo $alltables $thesetables` # change the schema itself mysql -e “ALTER DATABASE $database CHARACTER SET utf8 COLLATE ..
These are online, self-guided ways for developers wishing to gain more RDBMS understanding (or have a refresher course) in the two most ubiquitous platforms — MySQL and PostgreSQL. I add and remove from this list from time to time as material becomes outdated or better bits are found. Disclaimer: I didn’t have a hand in ..
If ever there was a TL;DR, this is it. However, it is important to understand the “whys” in my world, so here goes. A full discussion of character sets and encoding is beyond the scope of this document. (If you want more background, I recommend checking out the wikipedia article for a good place to ..