MySQL UUID function produces the same value when used as a function parameter

Question

The UUID() function by itself produces a different value each time it is called, as I would expect it to do:

SELECT UUID() from INFORMATION_SCHEMA.TABLES LIMIT 3;

3bb7d468-f9c5-11e9-8349-d05099466715
3bb7d482-f9c5-11e9-8349-d05099466715
3bb7d492-f9c5-11e9-8349-d05099466715

However, as soon as we use it within the REPLACE() function, it begins producing the same value:

SELECT REPLACE(UUID(),'-','-') from INFORMATION_SCHEMA.TABLES LIMIT 3;
e0f2d47a-f9c5-11e9-8349-d05099466715
e0f2d47a-f9c5-11e9-8349-d05099466715
e0f2d47a-f9c5-11e9-8349-d05099466715

This 'breaks' Insert From Select statements like this where we expect each inserted row to have a unique value:

INSERT INTO MyTable (uid, tableName) -- uid is binary(16)
SELECT UNHEX(REPLACE(UUID(),'-','')), TABLE_NAME from INFORMATION_SCHEMA.TABLES;

Note, I am using the information schema's list of tables for convenience. It shouldn't matter, but for those that are curious, our PK's are UUIDs in binary(16) form. I can't change that; please don't focus on that.

The UUID() function is non-deterministic, while the REPLACE() function is deterministic. I would have expected the non-deterministic characteristic of the UUID() function to result in the REPLACE() function behaving as if it had a different argument for each row, but it seems as though the DB engine is over optimizing by assuming the UUID() to be constant.

I also tested this behavior with another non-deterministic function, RAND(), and in this case the REPLACE() function worked as we'd expect!

SELECT REPLACE(RAND(),' ',' ') from INFORMATION_SCHEMA.TABLES LIMIT 3;
0.911571646026868
0.626416072832808
0.6977608461843439

Questions:

Is there a way to perform an "Insert From Select" and generate a unique UUID in binary 16 form per row in the select?

Why is this happening? Is this a bug?

---

Updates

I am using 5.7.27 locally:

mysql Ver 14.14 Distrib 5.7.27, for Linux (x86_64)

But this will end up deploying to an AWS RDS instance. lol... The Terraform (scripted deploy) spins up an AWS RDS instance with engine version 5.7.16.

Looking in the AWS console, I see support up to version 5.7.26 (in the 5.7 vein) and 8.0.16 (in the 8.0 vein). I'll discuss upgrading the deployed engine version. I'd love to change the PK column definitions to default the values as @Schwern has suggested.

---

Work Around

Until I can get others to agree to a version change, I'm moving forward by using a temporary table as intermediate storage for generated id values.

CREATE TEMPORARY TABLE GeneratedIds (
    generatedId varchar(36) NOT NULL,
    tableName text NOT NULL
);
INSERT INTO GeneratedIds (generatedId, tableName)
SELECT UUID(), TABLE_NAME from INFORMATION_SCHEMA.TABLES;

INSERT INTO MyTable (uid, tableName) -- uid is binary(16)
SELECT UNHEX(REPLACE(generatedId,'-','')), tableName FROM GeneratedIds;

DROP TABLE GeneratedIds;

This is not very elegant, but it does work. In my case I am working within a sql migration file where I can string together this kind of sequence of sql in a cohesive manner. I wouldn't recommend doing this in code; it smells.

---

Conclusion

This does appear to be a bug in MySQL. I did a quick search of their bug DB but I did not find a mention of it. Regardless, the SQL statements above illustrate the defect, and @Schwern and I have shown that this bug has been fixed in version 5.7.27 (exactly) and version 8.0.16 (possibly all 8.., only tested 8.0.16 and 8.0.18).

Version 8.0.16 test:

Server version: 8.0.16 MySQL Community Server - GPL

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SELECT REPLACE(UUID(),'-','-') from INFORMATION_SCHEMA.TABLES LIMIT 3;
+--------------------------------------+
| REPLACE(UUID(),'-','-')              |
+--------------------------------------+
| 96f9205a-fdc6-11e9-87de-d05099466715 |
| 96f920f9-fdc6-11e9-87de-d05099466715 |
| 96f9213e-fdc6-11e9-87de-d05099466715 |
+--------------------------------------+
3 rows in set (0.00 sec)

Answer 1

MySQL 5.6.46, 5.7.28, nor 8.0.18 do not appear to have this issue. Upgrade if you can.

One of the benefits of upgrading is you can now use functions as column defaults. This allows you to set the UUID as the default for your primary key sidestepping this and many other problems. You can also use uuid_to_bin and bin_to_uuid.

create table MyTable (
  uid binary(16) primary key default(uuid_to_bin(uuid())),
  tableName text not null
);

INSERT INTO MyTable (tableName)
SELECT TABLE_NAME from INFORMATION_SCHEMA.TABLES;

If you can't upgrade, you can use a trigger to set the default primary key as in this answer.