SQL - 关于在多列上将列转置为行的问题

Question

Here's my table

Table A

ID1, COL1, COL2, CODE A1, CODE A2, CODE A3,CODE B1, CODE B2, CODE B3, ..... CODE Z1, CODE Z2, CODE Z3  

Here's the output I want:

ID1, COL1, COL2, CODE A1, CODE A2, CODE A3
ID1, COL1, COL2, CODE B1, CODE B2, CODE B3
    .
    .
    .
ID1, COL1, COL2, CODE Z1, CODE Z2, CODE Z3

Basically I want every occurrence of the combination CODE A1, CODE A2, CODE A3 output as new row along with the first 3 columns that uniquely identifies the record.

Let's say there are 26 occurrences of the combination of three codes, which is 78 columns.

I want to see this record split into 26 records.

Any suggestions you have would be really helpful.

Answer 1

Many databases support the Standard SQL lateral joins, which is the best approach. But a more general approach is simply union all :

select id1, col1, col2, code_a1 as code from t union all
select id1, col1, col2, code_a2 as code from t union all
. . .