Simulate effective LEAD(1) or LEAD(2) in MySQL
Use MySQL 8, which supports Window Functions
Hack around it..


Generate a sequence of IDS. This whole project makes no sense without them anyway because the result set of a SQL query isn't guaranteed without an ORDER BY.
LEFT-OUTER JOIN the table with itself self join on id+1 = id

MySQL specific, emulate lag with user-defined variables


That looks something like this in MySQL,

SELECT t1.digit, t2.digit
FROM (
    SELECT digit, @rownum1 := @rownum1 + 1 AS id
    FROM
     alfabet  , (SELECT @rownum1 := 0) r
    ORDER BY
     alfabet.digit ASC
) AS t1
LEFT OUTER JOIN ( 
    SELECT digit, @rownum2 := @rownum2 + 1 AS id
    FROM
     alfabet  , (SELECT @rownum2 := 0) r
    ORDER BY
     alfabet.digit ASC
) AS t2
  ON t1.id +1 = t2.id;


You can even make that simpler with 

SELECT digit, previous
FROM (
    SELECT digit, @prev previous, @prev := digit AS prev
    FROM
     alfabet  , (SELECT @prev := '') r
    ORDER BY
     alfabet.digit ASC
) AS t1;