Question: I have a table of 5700 records. The primary key is an integer. Now I noticed that some values are missing. Like this:

```
100 data
101 data 
102 data
104 data

```

`103` is missing. How I can update all the rows so that the order becomes correct (`104` becomes `103` in my example) in one SQL command?

Answer: 
There is no point in doing this.

IDs from deleted records are not re-used on purpose - to make sure that references from other tables to previously deleted records don't suddenly point to the *wrong* record, for example. It is not a good idea to try to change this.

If you want a numbered list that has no holes, create a second `int` column that you re-order in your client program whenever necessary (i.e. when a record is deleted).
I'd advise against messing with your PKs unless you really have no choice, it can cause breakage all over the place when that id column is referred by other tables. If the PK really tolerates no gaps, maybe the choice of PK was not ideal... 

If you really think you should do this (and are sure nothing will break in other tables):

* create a table with the same structure as the original one, but use type serial for id
* copy data without id into that copy table - you'll now have a copy of original with thanks to serial a nice gapless id field
* empty original table (or faster, create an identical copy and drop original)
* copy data from copy table into original table including id