SQLite 3.8

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CREATE TABLE tablename (
	id	INTEGER,
	metric	TEXT
);
insert into tablename (id, metric) values
(1, '"123,456,789"'), (2, '"546,123,789"');
select * from tablename


id
metric


1
"123,456,789"

2
"546,123,789"


select id,
  substr(metric, 1, instr(metric, ',') - 1) col1,
  substr(substr(metric, length(substr(metric, 1, instr(metric, ',') - 1)) + 2), 1, instr(substr(metric, length(substr(metric, 1, instr(metric, ',') - 1)) + 2), ',') - 1) col2,
  substr(substr(metric, length(substr(metric, 1, instr(metric, ',') - 1)) + 2), instr(substr(metric, length(substr(metric, 1, instr(metric, ',') - 1)) + 2), ',') + 1) col2
from tablename 


id
col1
col2
col2


1
"123
456
789"

2
"546
123
789"


    with qry as (
      select 
        id, 
        substr(metric, 1, instr(metric, ',') - 1) col1, 
        substr(metric, instr(metric, ',') + 1) right1 from tablename
    )
    
    select 
      id, 
      col1, 
      substr(right1, 1, instr(right1, ',') - 1) col2, 
      substr(right1, instr(right1, ',') + 1) col3
    from qry q


id
col1
col2
col3


1
"123
456
789"

2
"546
123
789"