Question

我的桌子看起来像这样

mysql> select * from rc;

    +----+----------------------------+----------------------------+----------------------------+
    | id | business_date              | cutoff_dt                  | recon_dt                   |
    +----+----------------------------+----------------------------+----------------------------+
    |  1 | 2017-03-21 16:50:29.032000 | 2017-03-21 16:50:31.441000 | 2017-03-21 16:50:32.832000 |
    +----+----------------------------+----------------------------+----------------------------+
    1 row in set (0.00 sec)

我想运行查询

-select * from rc business_date = '2017-03-17' - if cutoff_dt`为null或为空，它将显示null，否则显示为null

我把它写进了shell脚本。

#! /bin/bash
mysql -u root -p <<rcard
use rcard;
SELECT * 
(CASE WHEN (cut_off_dt = "NULL")
    THEN
      echo "Null"
    ELSE
       echo "NOT NULL"
END)
from rc WHERE business_date = '2017-03-17';
rcard

但我收到错误

ERROR 1064 (42000) at line 2: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(CASE WHEN (cut_off_dt = "NULL")
    THEN
      echo "Null"
    ELSE
   ' at line 2

在MySQL中编写IF ELSE是正确的方法吗？

Answer 1

这不是检查NULL值的正确方法。

试试这个：

SELECT *,
       IF(mepslog_cut_off_dt IS NULL, 'NULL', 'NOT NULL')  
from rc_mepslog 
WHERE mepslog_business_date = '2017-03-17';

您也可以使用CASE表达式：

SELECT *,
       CASE 
          WHEN mepslog_cut_off_dt IS NULL THEN 'NULL'
          ELSE 'NOT NULL'
       END
from rc_mepslog 
WHERE mepslog_business_date = '2017-03-17';

Answer 2

SELECT *, (CASE WHEN (mepslog_cut_off_dt IS NULL)
    THEN
      'Null'
    ELSE
       'NOT NULL' END) from rc WHERE business_date = '2017-03-17'

要比较值是否为null，请使用column IS NULL代替column = 'NULL';后者会检查你要比较的列是否有字符串'null'

Answer 3

在select *之后缺少逗号，并且您在查询中指定的任何表名都不存在。要将表与列分开，请使用点.。还有其他错误的书面列名。此外，您不使用echo，只需指定要执行的操作。另外，我建议在案例（AS 'nullOrNotNull'）

中使用所选列的别名

SELECT * ,
CASE WHEN cut_off_dt IS NULL
    THEN
      'Null'
    ELSE
      'NOT NULL'
END AS 'nullOrNotNull'
from rc WHERE business_date = '2017-03-17';

在MYSQL中写入IF..ELSE

3 个答案: