验证帐号SQL表

Question

I'd like to select data from a table with the following rule, but I'm having trouble writing the query. I'm using PostgreSQL and I can't create a UDF. The table looks like this:

id  | user_id  | account_number
-------------------------------
 1  |    1     | 12345671
 2  |    4     | 12356673
 3  |    7     | 12325678

The id and user_id are integers whereas the account number is a string. I'd like to select the account numbers that match the following conditions:

• Account number string contains exactly 8 digits
• Validation scheme
  1. Take the first 7 digits
  2. Multiply the first digit by 1, the second by 2, the third by 3, the fourth by 1, the fifth by 2, the sixth by 3 and the seventh by 1
  3. Sum the result of multiplying each digit by the relevant number
  4. If the 8th digit is the same as mod(sum, 10) then select this number

In this table above, I should only return the first two rows with the query.

Just to repeat, I can't create a UDF, so am looking to find out whether this is possible using ordinary SQL in a query.

Thanks!

Answer 1

Yes, you can do it. Basically, use SIMILAR TO to check for exactly 8 digits, then substring and cast to do the math. Something like this:

SELECT * FROM table_name WHERE
  account_number SIMILAR TO '[0-9]{8}'
  AND (
    1 * CAST(SUBSTR(account_number, 1, 1) AS INTEGER) +
    2 * CAST(SUBSTR(account_number, 2, 1) AS INTEGER) +
    3 * CAST(SUBSTR(account_number, 3, 1) AS INTEGER) +
    1 * CAST(SUBSTR(account_number, 4, 1) AS INTEGER) +
    2 * CAST(SUBSTR(account_number, 5, 1) AS INTEGER) +
    3 * CAST(SUBSTR(account_number, 6, 1) AS INTEGER) +
    1 * CAST(SUBSTR(account_number, 7, 1) AS INTEGER)
  )%10 = CAST(SUBSTR(account_number, 8, 1) AS INTEGER)

Of course, this returns no rows in your example, because:

1×1 + 2×2 + 3x3 + 1×4 + 2×5 + 3×6 + 1×7 = 53
53 MOD 10 = 3
3 ≠ 1

PS: You do realize the UDFs can be written in languages other than CEg, you can write one in PL/pgSQL.

Answer 2

Just create a table where you split out your digits, then do the arithmetic (of course, you can fill in the rest of the stuff where the ... s are).

create table digits as
select account_number,
substr(account_number::text,0,1)::int as digit_1
,substr(account_number::text,1,1)::int as digit_2
,...
substr(account_number::text,7,1) as digit_8
from table
where account_number::text~E'[0-9]{8}'; --regex to make sure acct numbers are of the right form.

select account_number,
(digit_1+2*digit_2+...+3*digit_6+dight_7)%10=digit_8 as valid
from digits;

Of course, if you'd rather not create a separate table, you can always put the select statement for the creation of the digits table into a subquery for the second query.

Answer 3

select id, 
       user_id,
       digit_sum, 
       last_digit 
from (
  select id, 
         user_id,
         (substring(account_number,1,1)::int + 
          substring(account_number,2,1)::int * 2 + 
          substring(account_number,3,1)::int * 3 + 
          substring(account_number,4,1)::int + 
          substring(account_number,5,1)::int * 2 + 
          substring(account_number,6,1)::int * 3 +
          substring(account_number,7,1)::int ) as digit_sum, 
          substring(account_number,8,1)::int as last_digit
  from accounts
) t
where last_digit = digit_sum % 10

To make life easier, I would create a view that does the splitting and summing of the values. Then you just need to select from that view with the where condition I used for the derived table.

Answer 4

You can try something along these lines.

select *,   (
    (substring(account_number from 1 for 1)::integer * 1) +
    (substring(account_number from 2 for 1)::integer * 2) +
    (substring(account_number from 3 for 1)::integer * 3) +
    (substring(account_number from 4 for 1)::integer * 1) +
    (substring(account_number from 5 for 1)::integer * 2) +
    (substring(account_number from 6 for 1)::integer * 3) +
    (substring(account_number from 7 for 1)::integer * 1)
   ) as sums,
  (
    (substring(account_number from 1 for 1)::integer * 1) +
    (substring(account_number from 2 for 1)::integer * 2) +
    (substring(account_number from 3 for 1)::integer * 3) +
    (substring(account_number from 4 for 1)::integer * 1) +
    (substring(account_number from 5 for 1)::integer * 2) +
    (substring(account_number from 6 for 1)::integer * 3) +
    (substring(account_number from 7 for 1)::integer * 1)
   ) % 10 as mod_10
from acct_no
where length(account_number) = 8 

I wrote the calculation into the SELECT clause instead of the WHERE clause, because either my arithmetic is wrong or your specs are wrong.