How to store uuid as number?

Based on the answer of question, UUID performance in MySQL, the person who answers suggest to store UUID as a number and not as a string. I'm not so sure how it can be done. Anyone could suggest me something? How my ruby code deal with that?

If I understand correctly, you're using UUIDs in your primary column? People will say that a regular (integer) primary key will be faster , but there's another way using MySQL's dark side. In fact, MySQL is faster using binary than anything else when indexes are required.

Since UUID is 128 bits and is written as hexadecimal, it's very easy to speed up and store the UUID.

First, in your programming language remove the dashes

From 110E8400-E29B-11D4-A716-446655440000 to 110E8400E29B11D4A716446655440000.

Now it's 32 chars (like an MD5 hash, which this also works with).

Since a single BINARY in MySQL is 8 bits in size, BINARY(16) is the size of a UUID (8*16 = 128).

You can insert using:

INSERT INTO Table (FieldBin) VALUES (UNHEX("110E8400E29B11D4A716446655440000"))

and query using:

SELECT HEX(FieldBin) AS FieldBin FROM Table

Now in your programming language, re-insert the dashes at the positions 9, 14, 19 and 24 to match your original UUID. If the positions are always different you could store that info in a second field.

Full example :

CREATE TABLE  `test_table` (
    `field_binary` BINARY( 16 ) NULL ,
    PRIMARY KEY (  `field_binary` )
) ENGINE = INNODB ;

INSERT INTO  `test_table` (
    `field_binary`
)
VALUES (
    UNHEX(  '110E8400E29B11D4A716446655440000' )
);

SELECT HEX(field_binary) AS field_binary FROM `test_table`

If you want to use this technique with any hex string, always do length / 2 for the field length. So for a sha512, the field would be BINARY (64) since a sha512 encoding is 128 characters long.

The Percona blog has an article (that includes benchmarks) that replies to your question: Store UUID in an optimized way.

I don't think that its a good idea to use a binary.

Let's say that you want to query some value:

SELECT HEX(field_binary) AS field_binary FROM `test_table`

If we are returning several values then we are calling the HEX function several times.

However, the main problem is the next one:

SELECT * FROM `test_table`
    where field_binary=UNHEX('110E8400E29B11D4A716446655440000')

And using a function inside the where, simply ignores the index.

Also

SELECT * FROM `test_table`
    where field_binary=x'skdsdfk5rtirfdcv@#*#(&#@$9' 

Could leads to many problems.