使用AS

Question

我有简单的SQL：

SELECT TIMESTAMPDIFF(YEAR, bdate, CURDATE()) as age, id, bdate 
from  my_table
where age between 20 and 30

我收到了这个错误：

  

未知列＆＃39;年龄＆＃39;在＆＃39; where子句＆＃39;

Answer 1

您无法在where clause中使用别名，您需要在where子句中重用别名的公式或使用having clause或使用外部查询

SELECT TIMESTAMPDIFF(YEAR, bdate, CURDATE()) as age, id, bdate 
from  my_table
having age between 20 and 30

OR

select * from  (
 SELECT TIMESTAMPDIFF(YEAR, bdate, CURDATE()) as age, id, bdate 
 from  my_table
)x
where age between 20 and 30

Answer 2

MySQL中的WHERE子句中没有别名。

  

标准SQL不允许在WHERE子句中引用列别名。强制执行此限制是因为在评估WHERE子句时，可能尚未确定列值。   的 MySQL Docs

你必须使用

 WHERE TIMESTAMPDIFF(YEAR, bdate, CURDATE())  BETWEEN 20 AND 30