除非预期输出不完整，否则以下查询应返回预期结果：

select distinct woo.si_number, pnm.pn, stm.serial_number
from WO_OPERATION woo join parts_master pnm on woo.pnm_auto_key = pnm.pnm_auto_key
                      join companies cmp on cmp.cmp_auto_key = woo.cmp_auto_key
                      join wo_work_type wwt on wwt.wwt_auto_key = woo.wwt_auto_key
                      join stock stm on stm.pnm_auto_key = pnm.pnm_auto_key
where pnm.pn = '5A3307-7' AND
      stm.serial_number = 'BNG0776' AND
      wwt.description = 'OVERHAULED'
order by woo.si_number

• DISTINCT删除重复行。
• 如果只需要一个特定的serial_number-不要使用通配符。

通过添加DISTINCT进行查询，以获取woo.si_number和stm.serial_number的唯一值，同时仍然连接表。通过添加distinct，在执行查询后只返回unique：-

SELECT DISTINCT
  si_number,
  pn,
  company_name,
  description,
  serial_number
FROM
  (SELECT
    woo.si_number,
    pnm.pn,
    cmp.company_name,
    wwt.description,
    stm.serial_number
  FROM
    WO_OPERATION woo
  JOIN
    parts_master pnm ON woo.pnm_auto_key = pnm.pnm_auto_key
  JOIN
    companies cmp ON cmp.cmp_auto_key = woo.cmp_auto_key
  JOIN
    wo_work_type wwt ON wwt.wwt_auto_key = woo.wwt_auto_key
  JOIN
    stock stm ON stm.pnm_auto_key = pnm.pnm_auto_key
  WHERE
    pnm.pn = '5A3307-7' AND
    stm.serial_number LIKE 'BNG%' AND
    wwt.description = 'OVERHAULED') AS subquery
ORDER BY
  si_number;

每个si编号和pn需要一个结果行。因此，按这两列聚合数据（通过GROUP BY）。不清楚您要根据什么规则来选择每个si编号和pn的序列号。在下面的示例中，我取最小序列号。

select woo.si_number, pnm.pn, min(stm.serial_number) as serial_no
from wo_operation woo 
join parts_master pnm on pnm.pnm_auto_key = woo.pnm_auto_key
join stock stm on stm.pnm_auto_key = pnm.pnm_auto_key
where pnm.pn = '5A3307-7'
and stm.serial_number like 'BNG%' 
and woo.wwt_auto_key = 
(
  select wwt.wwt_auto_key
  from wo_work_type wwt
  where wwt.description = 'OVERHAULED'
)
group by woo.si_number, pnm.pn
order by woo.si_number;