当 3 个表(表 A、表 B 和表 C)中的每一个都存在一行或多行时,下面所示的查询将起作用并返回所有行。
但是,当连接的表之一(特别是我的情况下的表 C)没有行时,查询将失败并且不返回任何内容。
我需要下面的查询才能在表 B 或表 C 可能没有任何行的情况下工作。
$query_string = '
SELECT tableA.*,
GROUP_CONCAT(DISTINCT tableB.tbID ORDER BY tableB.sortOrder) AS tbID,
GROUP_CONCAT(DISTINCT tableC.tcID ORDER BY tableC.sortOrder) AS tcID,
tableD1.fullName AS createdByFullName,
tableD2.fullName AS lastUpdatedByFullName
FROM table_A AS tableA
INNER JOIN table_B AS tableB ON tableA.ID = tableB.ID
INNER JOIN table_C AS tableC ON tableA.ID = tableC.ID
LEFT JOIN table_D AS tableD1 ON tableD1.ID = tableA.createdBy
LEFT JOIN table_D AS tableD2 ON tableD2.ID = tableA.lastUpdatedBy
WHERE tableA.ID = "' . $this_ID . '"
GROUP BY tableB.ID, tableC.ID
LIMIT 1
';
这是表格
table_A
+----+------+------+-----------+---------------+
| ID | col1 | col2 | createdBy | lastUpdatedBy |
+----+------+------+-----------+---------------+
| 01 | data | data | 02 | 01 |
| 02 | data | data | 03 | 02 |
| ... |
| 99 | data | data | 01 | 02 |
+----+------+------+-----------+---------------+
table_B
+----+------+-----------+
| ID | tbID | sortOrder |
+----+------+-----------+
| 01 | 01 | 2 |
| 01 | 02 | 1 |
| 02 | 01 | 2 |
| 02 | 02 | 3 |
| 02 | 03 | 1 |
| 99 | 01 | 1 |
+----+------+-----------+
table_C (query works when $this_ID="02" exists)
+----+------+-----------+
| ID | tcID | sortOrder |
+----+------+-----------+
| 01 | 01 | 1 |
| 02 | 01 | 2 |
| 02 | 02 | 1 |
| 99 | 01 | 1 |
+----+------+-----------+
table_C (query does not work when $this_ID="02" does not exist)
+----+------+-----------+
| ID | tcID | sortOrder |
+----+------+-----------+
| 01 | 01 | 1 |
| 99 | 01 | 1 |
+----+------+-----------+
table_D (this table is not relevant to the example, but exists in my query)
+----+------------+
| ID | fullName |
+----+------------+
| 01 | John Doe |
| 02 | Mary Jones |
| 03 | Joe Smith |
+----+------------+
这是我尝试过的方法(均未成功):
T&E #1
GROUP_CONCAT(DISTINCT tableB.tbID ORDER BY tableB.sortOrder) AS tbID,
GROUP_CONCAT(DISTINCT tableC.tcID ORDER BY tableC.sortOrder WHERE tableC.ID <> "") AS tcID,
T&E #2
WHERE tableA.ID = "' . $this_ID . '" AND tableC.ID <> ""
注释:我专门测试表 C,但如果表 B 中也没有相关行,我需要相同的解决方案才能工作。谢谢。
最佳答案
一个简单的LEFT JOIN
应该可以解决这个问题。
即使表C
中不存在,这也会给出表A
的结果,但如果存在则显示它们。这要求表 B
中存在数据关系。
将其更改为 LEFT JOIN
(如果情况不应该如此)。
SELECT tableA.*,
GROUP_CONCAT(DISTINCT tableB.tbID ORDER BY tableB.sortOrder) AS tbID,
GROUP_CONCAT(DISTINCT tableC.tcID ORDER BY tableC.sortOrder) AS tcID,
tableD1.fullName AS createdByFullName,
tableD2.fullName AS lastUpdatedByFullName
FROM table_A AS tableA
INNER JOIN table_B AS tableB ON tableA.ID = tableB.ID
LEFT JOIN table_C AS tableC ON tableA.ID = tableC.ID
LEFT JOIN table_D AS tableD1 ON tableD1.ID = tableA.createdBy
LEFT JOIN table_D AS tableD2 ON tableD2.ID = tableA.lastUpdatedBy
WHERE tableA.ID = "' . $this_ID . '"
GROUP BY tableB.ID, tableC.ID
LIMIT 1
关于mysql - 如何使用 GROUP_CONCAT() 排除没有相关行的连接表,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22326293/