我需要一个if语句来创建一个名为“part_ID”的字段。该字段采用字段“p.ID”并在“a.Part_ID”中查找。如果part_ID在“a.Part_ID”中不为空，则部件ID应保持不变，只是“a.Part_ID”。如果零件ID为空，则它应在“b.Part_ID_Not_cataloged”中查找零件ID，如果列出零件ID，则应将其替换为“b.related_Part_ID_in_catalog”。
SELECT a.Part_ID, p.ID, b.Part_ID_Not_cataloged, b.related_Part_ID_in_catalog
FROM (SYSADM_PART AS p
LEFT JOIN tbl_concatenated_data_view_only AS a ON p.ID = a.Part_ID)
LEFT JOIN tbl_Part_ID_Not_in_catalog_entry AS b ON p.ID = b.Part_ID_Not_cataloged;