Mysql：使用大小写仅列出非空值

我尝试使用查询仅列出NOT NULL值：

SELECT 
        firm.ShortName AS companyshortname,
        firm.ExtRefId AS compextrefid,
        finrnd.dealDate AS dealdate,
        (CASE
            WHEN (ent.EntityType = 'Firm') THEN afirm.ShortName
            WHEN (ent.EntityType = 'Partnership') THEN pship.ShortName
            WHEN
                (ent.EntityType = 'Individual')
            THEN
                CONCAT(ind.LastName,
                        ', ',
                        ind.FirstName)
        END) AS investor,
        (CASE
            WHEN (ent.EntityType = 'Firm' AND afirm.ExtRefId IS NOT NULL)  THEN afirm.ExtRefId
            WHEN (ent.EntityType = 'Partnership' AND pship.ExtRefId IS NOT NULL) THEN pship.ExtRefId
            WHEN (ent.EntityType = 'Individual' AND ind.ExtRefId IS NOT NULL) THEN ind.ExtRefId
        END) AS investorextrefid,
         finrndinv.isLeadInvestor AS isleadinvestor
    FROM
        ((((((financinginvestors finrndinv
        JOIN financingrounds finrnd ON ((finrnd.financingid = finrndinv.financingid)))
        JOIN firms firm ON ((firm.FirmEntID = finrnd.compentid)))
        LEFT JOIN entities ent ON ((ent.InvEntID = finrndinv.investorid)))
        LEFT JOIN firms afirm ON ((afirm.FirmEntID = ent.InvEntID)))
        LEFT JOIN individuals ind ON ((ind.IndEntID = ent.InvEntID)))
        LEFT JOIN partnerships pship ON ((pship.PShipEntID = ent.InvEntID)));

但是在运行代码时，对于名为

investorextrefid

的列，我确实会得到空值。我不确定我在案例中的WHEN子句中添加的条件是否是正确的方法。此查询给出的结果与案例中WHEN子句中没有AND部分的结果相同

+------------------+--------------+---------------------+----------------------------------+------------------+----------------+
| companyshortname | compextrefid | dealdate            | investor                         | investorextrefid | isleadinvestor |
+------------------+--------------+---------------------+----------------------------------+------------------+----------------+
| Access Insurance | ASP:143      | 2019-06-06 00:00:00 | ASP                              | NULL             |              0 |
| Access Insurance | ASP:143      | 2019-06-06 00:00:00 | Russell 2000                     | NULL             |              0 |
| Access Insurance | ASP:143      | 2019-06-06 00:00:00 | Addiko Bank                      | ASP:62           |              0 |
| Access Insurance | ASP:143      | 2019-06-06 00:00:00 | Universal American Financial Cor | ASP:119          |              0 |
| Access Insurance | ASP:143      | 2019-06-06 00:00:00 | Lever, Inc                       | ASP:131          |              1 |
+------------------+--------------+---------------------+----------------------------------+------------------+----------------+

---

获取空值的原因是您没有

ELSE

案例

因此，如果要在不满足任何条件时替换结果集中的NULL值 您只需添加和

ELSE

case即可：

...
WHEN (ent.EntityType = 'Individual' AND ind.ExtRefId IS NOT NULL) THEN ind.ExtRefId 
ELSE 'Some other value' 
END) AS investorextrefid,
...

另一方面，如果您想完全删除这些行，您只需在查询的末尾添加WHERE条件，如下所示：

WHERE 
(ent.EntityType = 'Firm' AND afirm.ExtRefId IS NOT NULL) 
OR (ent.EntityType = 'Partnership' AND pship.ExtRefId IS NOT NULL) 
OR (ent.EntityType = 'Individual' AND ind.ExtRefId IS NOT NULL)

---

您的CASE函数中没有编码ELSE。因此，如果有任何值使得条件为真时3个值都不存在，investorextrefid将设置为NULL。请尝试添加：

ELSE CONCAT（ent.EntityType'，if（ISNULL（ind.ExtRefId），'NULL'，ind.ExtRefId））

以查看ELSE情况。@Ronaldaronson感谢您的回复，我想的是，如果行本身为空，我怎么排除它呢？为什么我没有想到这一点？感谢您的回复，它成功了。：）

WHERE 
(ent.EntityType = 'Firm' AND afirm.ExtRefId IS NOT NULL) 
OR (ent.EntityType = 'Partnership' AND pship.ExtRefId IS NOT NULL) 
OR (ent.EntityType = 'Individual' AND ind.ExtRefId IS NOT NULL)