Combine Multiple Rows Results From Left Join in a unique cell
You can use a subquery and a GROUP_CONCAT for that
Schema (MySQL v8.0)
CREATE TABLE Table1 (
  `FieldID` INTEGER,
  `FieldName` VARCHAR(3),
  `FieldAccount` INTEGER
);

INSERT INTO Table1
  (`FieldID`, `FieldName`, `FieldAccount`)
VALUES
  ('01', 'Jon', '12345');

CREATE TABLE Table2 (
  `FieldID` INTEGER,
  `FieldName` VARCHAR(7),
  `FieldAccount` INTEGER
);

INSERT INTO Table2
  (`FieldID`, `FieldName`, `FieldAccount`)
VALUES
  ('01', 'Jon', '12345'),
  ('02', 'Charlie', '12345');


Query #1
SELECT
t1.*
,(SELECT GROUP_CONCAT(`FieldID`) FROM Table2 WHERE `FieldAccount` = t1.`FieldAccount`
) 'LookAt '
FROM Table1 t1;

| FieldID | FieldName | FieldAccount | LookAt  |
| ------- | --------- | ------------ | ------- |
| 1       | Jon       | 12345        | 1,2     |


View on DB Fiddle