Question

SELECT `01` FROM perf WHERE year = '2013' order by CAST(`01` AS INT) LIMIT 3

列01的数值为varchar。我需要将'01'的前3个整数排序。为什么这个查询不起作用？

这样的表;

+----------------------+
| name | 01 | 02 | year|
+----------------------+
|name1 | 90 |*** |2013 |
+----------------------+
|name2 | 93 | 55 |2013 |
+----------------------+
|name3 |*** | 78 |2013 |
+----------------------+

查询应按01排序（忽略 * ）并提供名称和值。

Answer 1

MySQL不允许你CAST('01' AS INT)。它需要SIGNED或UNSIGNED。

SELECT `01` FROM perf WHERE year = '2013' order by CAST(`01` AS SIGNED) LIMIT 3

查看MySQL docs on CAST()以获取完整详情。

mysql> SELECT CAST('01' AS SIGNED);
+----------------------+
| CAST('01' AS SIGNED) |
+----------------------+
|                    1 |
+----------------------+
1 row in set (0.00 sec)

要强制最后对非数字字符串进行排序，您需要在CASE中应用ORDER BY，这会为它们分配一个荒谬的高值。条件应该测试01中的值不等于0，和，当投放到SIGNED时，结果不是0，由于非数字字符串将被转换为零。

如果不满足这些条件，则假定该字符串为非数字，并在ORDER BY中给出值999999999，将其推送到最后。它们随后由name订购。

SELECT * FROM perf 
WHERE year = '2013'
ORDER BY
  CASE WHEN (`01` <> '0' AND CAST(`01` AS SIGNED) <> 0) THEN CAST(`01` AS SIGNED) ELSE 999999999 END,
  name
LIMIT 3

http://sqlfiddle.com/#!2/846e2/6

要使这些排序降序，请使用荒谬的低值（负值）而不是高值

  CASE WHEN (`01` <> '0' AND CAST(`01` AS SIGNED) <> 0) THEN CAST(`01` AS SIGNED) ELSE -999999999 END DESC,

MySQL顺序（str到int）

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