PostgreSQL – How to Clean Non-Digit Except + at Beginning with Regexp_Replace

If you only have a few variables I would consider keeping separate boolean columns.

• Indexing is easy. In particular, indexes on expressions are easy.
• Conditions for queries and partial indexing are easy to write and read and meaningful.
• A boolean column occupies 1 byte. For only a few variables this occupies the least space.
• Unlike the other options boolean columns allow NULL values for individual bits if you should need that. You can always define columns NOT NULL if you don't.

Optimizing storage

If you have more than a hand full variables but less than 33, an integer column may serve you best. (Or a bigint for up to 64 variables.)

• Occupies 4 bytes on disk.
• Very fast indexing for exact matches (= operator).
• Handling individual values may be slower / less convenient than with bit string or boolean.

With even more variables, or if you want to manipulate the values a lot, or if you don't have huge tables and disk space / RAM is no issue, or if you are not sure what to pick, I would consider bit(n) or bit varying(n).

• Occupies at least 5 bytes (or 8 for very long strings) plus 1 byte for each group of 8 bits (rounded up).
• You can use bit string functions and operators directly.

Examples

For just 3 bits of information, individual boolean columns get by with 3 bytes, an integer needs 4 bytes and a bit string 6 bytes (5 + 1).

For 32 bits of information, an integer still needs 4 bytes, a bit string occupies 9 bytes for the same (5 + 4) and boolean columns occupy 32 bytes.

Further reading

• Is there any difference between integer and bit(n) data types for a bitmask?
• Calculating and saving space in PostgreSQL
• Can I convert a bunch of boolean columns to a single bitmap in PostgreSQL?

If you can live with losing some values to the maximum value, you could combine a sequence with a fixed offset to get the 20 digits. I would also define a check constraint on the table to to make sure that accidental inserts without using the default value insert the wrong value:

create sequence my_sequence_name;
create table foo 
(
   id numeric(20,0) default 10000000000000000001 + nextval('my_sequence_name'),
   constraint check_range check (id between 10000000000000000001 and 99999999999999999999)
);

That will give you a maximum generated value of 19223372036854775808 which doesn't use the complete range of allowed values, but it might be enough for your needs.