MySQL找到密集的系列缺口

Question

I have a "sequence" column of a Mysql table with a unique key, this should start from value of 1 to n.

create table myTest( id INT, ...,  sequence INT ..)

This column should represents a dense serie, so I don't want gaps into it, my question is: how can I find possible gaps?

My first idea is to insert into a temporary 1 column table all values from 1 to max(sequence) with a loop.

create temporary table allvalues( value INT)

Then select all elems of this temp table where values are not in myTest table:

select value from allvalues where value is not in (select sequence from myTest)

Is there any other better/fastest solution?

Answer 1

This another idea, this doesn't find every gap but only the ending gap in case of contiguous gaps:

select m1.sequence-1 from myTest m1
where m1.sequence>1 and not exists
  (select * from myTest m2 where m2.sequence=m1.sequence-1)

http://sqlfiddle.com/#!9/64f32/1