Question

Is there a way to determine whether a table, a very large table possibly, has contiguous / consecutive auto increment primary key IDs? Is there a SQL query way to determine this? Suppose someone deletes some rows randomly from a very large table. I need to know that this has happened.

e.g. 
table XYZ
id
1
2
3
4

table abc
1
2
4 <--- non contiguous, skipped 3
5

Curious about data integrity. I want a SQL query methodology way in order to just keep things simple and not have to write a PHP script to run against the database.

Answer 1

You could compare these two values:

SELECT (MAX(ID) - MIN(ID)) + 1, -- e.g. ID 2 - ID 1 = 1 (+1) = 2 rows
       COUNT(ID)
FROM Table

If the table is still contiguous they will be the same.