mysql - 随机行更新

Question

有时表中的行数超过 100 万行。

每个批处理将有 100,000 个随机行。

随机化行的最佳方法是什么？

我执行以下操作:

UPDATE  temp1 SET  `batch` =  '';
UPDATE  temp1 SET  `batch` =  'B1' WHERE batch = '' order by rand(number) limit 100000;
UPDATE  temp1 SET  `batch` =  'B2' WHERE batch = '' order by rand(number) limit 100000;
UPDATE  temp1 SET  `batch` =  'B3' WHERE batch = '' order by rand(number) limit 100000;
UPDATE  temp1 SET  `batch` =  'B4' WHERE batch = '' order by rand(number) limit 100000;
UPDATE  temp1 SET  `batch` =  'B5' WHERE batch = '' order by rand(number) limit 100000;

Answer 1

如果您不需要每批正好有 100000 条记录，您可以使用 rand() 构建随机批处理字符串，从统计上看，每批应该有大约 100000 条记录

UPDATE temp1
JOIN   (
    SELECT number, CONCAT('B',CONVERT( FLOOR( RAND() * (nrows/10) ) + 1, CHAR(19) )) AS randBatch
    FROM   temp1
    CROSS JOIN ( SELECT COUNT(*) AS nrows FROM temp1 ) as x
   ) AS y
ON     y.number = temp1.number
SET    batch = randBatch

SQL fiddle :http://sqlfiddle.com/#!9/eb161/1