mysql生成uuid,MySQL为多行生成UUID（）

I'm trying to add UUIDs to some tables in some of my MySQL databases (MySQL 5.7.9). First of all, I start by adding a column to receive the UUIDs:

ALTER TABLE `mytable` ADD COLUMN `Uuid` BINARY(16) DEFAULT NULL;

Then, for all entries that are already in the table, I generate UUIDs (since every entry in the DB will have received a NULL value in it's UUID field.

UPDATE `mytable` SET Uuid= unhex(replace(uuid(),'-','')) WHERE Uuid IS NULL;

Now, the thing is that I get some very weird behaviour by doing this; on some of my databases, every UUID generated is unique (as expected). However, on other databases, all generated UUIDs are identical (not similar, identical).

I suspect that this is due to the MySQL query optimiser, since behaviour is not consistent between different database instances (all on MySQL 5.7.9). However, I have no clue how to solve this issue.

So, MySQL gurus, am I doing something wrong?

解决方案

I had the same problem, but the solution was a later answer to the linked question. I had a default character set of utf8mb4, and the theory is that it implicitly converts uuid()'s utf8 result to a constant string, before the sql executes. Converting the other parameters to utf8 avoids that:

UPDATE `mytable` SET Uuid= unhex(replace(uuid(), _utf8'-', _utf8'')) WHERE Uuid IS NULL;

The later answer links to the relevant (not a) bug report. This SO issue looks related.