Mysql返回默认值，即使join不返回任何记录

Question

I have 4 tables that I join by using this query below. Given my data below, it wont actually return any because there are no records in the TRANSACTION_LINE with a line object type value of 6.

I want this query to return a default value of key_1 from EX_WORK, null line_Id, default value of 'OFF' on the TENDER_CODE if the query does not return any records.

I already tried coalesce and ifnull but seemed that it did not work. Can this be fixed by doing a left join instead of the inner?

Thanks!

SELECT  w.key_1 as if_entry_no, 
           l.line_id as line_id, 
           o.object_export_code as tender_code
      FROM EX_WORK w,
           transaction_header h, 
           transaction_line l, 
           line_object o 
     WHERE w.key_1 = h.if_entry_no
       AND h.transaction_void_flag in (0,8)
       AND h.if_entry_no = l.if_entry_no
       AND l.line_object_type = 6
       AND l.line_action <> 55 
       AND (l.line_action <> 72 OR h.tender_total = 0)  
       AND l.line_object = o.line_object

EX_WORK
serial_no   key_1   
111         2879051 

TRANSACTION_HEADER
if_entry_no store_no transaction_void_flag tender_total
2879051     9500     0                     0

TRANSACTION_LINE
if_entry_no line_Id line_object_type line_object line_action
2879051     1       14               9109        38
2879051     2       1                9105        99
2879051     3       5                9501        98
2879051     4       11               9111        46

LINE_OBJECT
line_object line_object_type    resource_id object_export_code
9105        1                   5529        null
9109        1                   5533        null
9111        1                   5535        null
9501        1                   5709        null

Answer 1

Yes, you want a left join. Something like this:

SELECT if_entry_no, line_id, ifnull(o.object_export_code, "OFF") AS tender_code
FROM (SELECT w.key_1 AS if_entry_no, l.line_id AS line_id, l.line_object
      FROM EX_WORK w,
           transaction_header h,
           transaction_line l,
           line_object o
      WHERE w.key_1 = h.if_entry_no
        AND h.transaction_void_flag IN (0, 8)
        AND h.if_entry_no = l.if_entry_no
        AND l.line_object_type = 6
        AND l.line_action <> 55
        AND (l.line_action <> 72 OR h.tender_total = 0)) s
       LEFT JOIN line_object o ON s.line_object = o.line_object;