如何获得不同的记录，但仅基于 MySQL 中的前 2 位数字

Question

I want to get distinct records (only one field) from a MySQL table, and that field contain only digits.

Example:

00010000
01111100
01112000
01118000
02301201

But distinct records is considered on base on first 2 digits. So in the case above, I need to get back only 3 records:

00010000
01112000
02301201

More over, I would like to trim the rest of the digits, so the actual end result should be:

00
01 
02

So distinct and group by will not cut here. Any idea?

Answer 1

Assuming you wanted the least value from among duplicates, you could try:

SELECT t1.col
FROM yourTable t1
INNER JOIN
(
    SELECT LEFT(col, 2) AS prefix, MIN(col) AS min_col
    FROM yourTable
    GROUP BY LEFT(col, 2)
) t2
    ON LEFT(t1.col, 2) = t2.prefix AND
       t1.col = t2.min_col;

Note: Numbers in MySQL don't start with zeroes, so your requirement (and this answer) only make sense if your column is text.

Answer 2

DISTINCT will work fine with LEFT to give the results you want:

SELECT DISTINCT(LEFT(value, 2)) AS value
FROM data
ORDER BY value 

Output

00
01
02

Demo on dbfiddle

Answer 3

If you only want the trimmed value, try this:

SELECT SUBSTRING(yourColumn,1,2) as trimmedval
FROM Table
GROUP BY SUBSTRING(yourColumn,1,2)