xxNcYnGR

1Improve MySQL basic update performance using MyISAM tables with 36 Million records
2CREATE  TABLE IF NOT EXISTS `mydb`.`africaPop` (
3  `geokey` VARCHAR(14) NOT NULL ,
4  `xpos` DECIMAL(7) NULL ,
5  `ypos` DECIMAL(7) NULL ,
6  `cellvalue` DECIMAL(14,5) NULL DEFAULT -9999 ,
7  `classCode` INT(11)  NULL DEFAULT -9999 ,
8  `classColour` VARCHAR(9) NULL DEFAULT NULL ,
9  PRIMARY KEY (`geokey`) ,
10  INDEX `IDXVALUE` (`cellvalue` ASC) );
11	
12update africaPop set classCode = -9999;
13	
14update africaPop set classCode = 10 where cellvalue BETWEEN 0 AND 25;