即使join没有返回任何记录，Mysql也会返回默认值

Question

我在下面使用此查询加入了4个表。鉴于我的数据如下，它实际上不会返回任何数据，因为TRANSACTION_LINE中没有行对象类型值为6的记录。

我希望此查询从EX_WORK返回默认值key_1，null line_Id，默认值为＆＃39; OFF＆＃39;如果查询没有返回任何记录，则在TENDER_CODE上。

我已经尝试过coalesce和ifnull，但似乎它没有用。可以通过左连接而不是内连接来解决这个问题吗？

谢谢！

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

是的，您想要左联接。像这样：

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;