为什么此查询返回空行？

Question

我有这种格式的数据

CREATE TABLE IF NOT EXISTS `historical_data` (
  `symbol_name` varchar(70) DEFAULT NULL,
  `current_day` varchar(50) DEFAULT NULL,
  `open_val` varchar(20) DEFAULT NULL,
  `high_val` varchar(20) DEFAULT NULL,
  `low_val` varchar(20) DEFAULT NULL,
  `close_val` varchar(20) DEFAULT NULL,
  `last_val` varchar(20) DEFAULT NULL,
  `prevclose_val` varchar(20) DEFAULT NULL,
  UNIQUE KEY `symbol_name` (`symbol_name`,`current_day`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;


INSERT INTO `historical_data` (`symbol_name`, `current_day`, `open_val`, `high_val`, `low_val`, `close_val`, `last_val`, `prevclose_val`) VALUES
    ('IBWSL', '10-DEC-2015', '9.35', '9.8', '9', '9.45', '9.6', '9.5'),
    ('ICICIBANK', '10-DEC-2015', '260.85', '261.9', '256', '258.95', '258.65', '259.45'),
    ('ICIL', '10-DEC-2015', '981', '1004.2', '981', '989.7', '992', '988.45'),
    ('ICNX100', '10-DEC-2015', '86.8', '87.99', '86.8', '87', '87', '82.5'),
    ('ICRA', '10-DEC-2015', '4175', '4280', '4144', '4211.4', '4279.95', '4175.3'),
    ('ZYDUSWELL', '14-DEC-2015', '815.75', '815.75', '785.25', '810.7', '810.5', '803.1'),
    ('ZYLOG', '14-DEC-2015', '2.9', '2.95', '2.85', '2.95', '2.95', '2.19');
/*!40000 ALTER TABLE `historical_data` ENABLE KEYS */;

我是这样写查询的

select * from (
    select 
      symbol_name , 
      (prevclose_val-close_val) as losers,
      'daily' as `type` 
    from
      historical_data
    where
      current_day >= STR_TO_DATE('14-DEC-2015', '%d-%MMM-%Y')
    order by losers asc limit 10 
) as sub_daily

这是我的 sqlfiddle

http://sqlfiddle.com/#!9/b4819

Answer 1

同时使用 STR_TO_DATE() 函数，因为您已将日期存储为数据库中的 varchar 列。

您还可以使用 DATE 作为 DATATYPE 在所有查询中删除此类日期转换

试试这个：

SELECT * 
FROM (SELECT symbol_name , (prevclose_val-close_val) AS losers,'daily' AS `type` 
      FROM historical_data 
      WHERE STR_TO_DATE(current_day, '%d-%M-%Y') >= STR_TO_DATE('14-DEC-2015', '%d-%M-%Y') 
      ORDER BY losers ASC 
      LIMIT 10 
     ) AS sub_daily;

勾选SQL FIDDLE DEMO

::输出::

| symbol_name |              losers |  type |
|-------------|---------------------|-------|
|   ZYDUSWELL |  -7.600000000000023 | daily |
|       ZYLOG | -0.7600000000000002 | daily |

Answer 2

您的问题是因为您将字段 current_day 创建为 VARCHAR，它应该是 DATE.

此外，在您的查询中，您仅将要过滤的值转换为日期，而不是字段本身。

因此，您应该修复 table 将该字段更改为在查询中执行此操作的日期 where 过滤器：

在 MySQL 文档中没有 %MMM 格式要么将其更改为 %b 缩写月份或 %M 月份名称格式参数遵循 DATE_FORMAT函数格式，看这里：DATE_FORMAT Formats

select * 
  from (select symbol_name , 
               (prevclose_val-close_val) as losers, 
               'daily' as `type` 
          from historical_data 
         where STR_TO_DATE(current_day, '%d-%b-%Y') >= STR_TO_DATE('14-DEC-2015', '%d-%b-%Y')  
         order by losers asc limit 10 
       ) as sub_daily

如果将该字段转换为 DATE 类型，您只需：

select * 
  from (select symbol_name , 
               (prevclose_val-close_val) as losers, 
               'daily' as `type` 
          from historical_data 
         where current_day >= '2015-12-14'  
         order by losers asc limit 10 
       ) as sub_daily

为什么此查询返回空行？

Why this query is returning empty rows?

mysql

sql

date

select

str-to-date