Mysql – Auto increment id column vs index VARCHAR columns

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I'm wondering the differences or comparisons of having an Auto Increment int Id column or an indexed VARCHAR(32) column. Which one would be faster if I had a second table that references the first table by joining? Like in the second table, would I store the Auto Increment INT id or the indexed VARCHAR column? What are the advantages or disadvantages, if any?

Which would be the more common practice? Create Auto Increment id column for almost every table? Or we can simply index a column that has a unique 36-char ID (like in SugarCRM) so the other tables can just use that when doing joins? I hope I explained my question fairly clear.

Best Answer

UUIDs are terrible when the table becomes too large to be cached. (If your table will never get very big, you can ignore the rest of my rant.)

The problem comes with the randomness of UUIDs. You fetch one row; it's in one place. You fetch another row, it is extremely likely to be in some other block. This leads to lots of I/O.

In contrast, AUTO_INCREMENT ids are inserted in roughly chronological order. A bunch (say, 100) rows will land in one block before moving on to the next block. This makes INSERTs efficient. It often makes reads efficient, too -- because often you are looking for records of similar vintage -- such as with a date range.

Think of News articles. Most people look at the latest news; the older records collect dust in the cache until they are bumped out. So, the cache tends to keep the latest rows. With UUIDs, old and new articles share the same block.

More on UUIDs.

Related Solutions

Mysql – How to make MySQL auto increment in random order

Here's what I would do. I hope I did understand your question correctly. It's a workaround and perhaps not very elegant:

create a random field, and then an AUTO_INCREMENT field ("ID") as the single field of a primary key, order by RND etc
create a temporary table with MIN(ID) for each combination of Col1/2 (first, but randomly):


SELECT
  MIN(ID) AS MIN_ID, Col1, Col2 
FROM 
  table 
GROUP BY 
 Col1, Col2

add a second INT field to be the first_index
update the table and set first_index to be the difference between the minimum value and the running value of the autoincremented field:


UPDATE 
  table t, temp_table tmp
SET 
  t.first_index = (t.ID - tmp.MIN_ID) + 1
WHERE 
  t.Col1=tmp.Col1 AND t.Col2=tmp.Col2

optionally remove the random and ID field, and add a new PK with the three fields Col1/Col2/first_index (auto incremented) for following inserts

Mysql – Advantages and Disadvantages to using ENUM vs Integer types

I found a very bizarre but informative article about 8 reasons why one should not use ENUM.

Even without the article, I know

there is no easy method for adding new values, some techniques are very high risk
numbers should never be used
only use strings (@DTest already mentioned this in his answer)

Best Answer

Related Solutions

Mysql – How to make MySQL auto increment in random order

Mysql – Advantages and Disadvantages to using ENUM vs Integer types

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