MySQL查询的顺序和限制

Question

Assume data like:

table: shapes

id    type
----------------
1     Square
2     Rectangle
3     Square
4     Square

When I execute the following query:

SELECT `shapes`.* FROM `shapes` WHERE `shapes`.`type` = 'Square' ORDER BY shapes.id DESC LIMIT 1

I would expect to receive a row with id: 4. Unexpectedly, I'm receiving a row with id: 1.

For the really strange part: If I execute the same query with LIMIT 2 :

SELECT `shapes`.* FROM `shapes` WHERE `shapes`.`type` = 'Square' ORDER BY shapes.id DESC LIMIT 2

The first row in that set of 2 is actually the correct row!

And to add to the strangeness still, I have another copy of this database within the same MySQL server, and it returns the correct row for any limit query, LIMIT 1 or otherwise.

The only answer I can come to is to dump and reload the database, but I'd like to understand why this is happening first before taking that action, if possible.

tl;dr: LIMIT 1 returns the wrong row. LIMIT 2 returns the correct row (for the first one). Seems to be database specific.

Answer 1

The problem is caused as you are not using limit 0, 1. While not provided the full query sometimes it display wrong results. I suggest you to type/execute the full query.