SQL to find the first occurrence of sets of data in a table

Question

Say if I have a table:

CREATE TABLE T
(
    TableDTM  TIMESTAMP  NOT NULL,
    Code      INT        NOT NULL
);

And I insert some rows:

Answer 1

could you try something like

"SELECT DISTINCT Code, (SELECT MIN(TableDTM) FROM T AS Q WHERE Q.Code = T.Code) As TableDTM FROM T;"

and if you need to exclude the 0, change it in:

 SELECT DISTINCT Code, (SELECT MIN(TableDTM) FROM T AS Q WHERE Q.Code = T.Code) As TableDTM FROM T WHERE Code <> 0;