Using alias name in another column

这个问题是延长我的前面的问题的一部分， 查找字符串号位置 。

我有表myTable如下（myWord ==> VARCHAR（10））

++++++++++++
+ myWord   +    
++++++++++++
+ AB123    +
+ A413     +
+ X5231    +
+ ABE921   +
+ 15231    +
+ 523      +
+ ABC      +
++++++++++++

我想，如下是。

++++++++++++++++++++++++++++++++
+ myWord   + myPos + NewString +
++++++++++++++++++++++++++++++++
+ AB123    + 3     + AB        +
+ A413     + 2     + A         +
+ X5231    + 2     + X         +
+ ABE921   + 4     + ABE       +
+ 15231    + 1     +           +
+ 523      + 1     +           +
+ ABC      + 999   + ABC       +
++++++++++++++++++++++++++++++++

要得到上面的输出，我用下面的查询。

SELECT 
  myWord, 
  LEAST (
    if (Locate('0',myWord) >0,Locate('0',myWord),999),
    if (Locate('1',myWord) >0,Locate('1',myWord),999),
    if (Locate('2',myWord) >0,Locate('2',myWord),999),
    if (Locate('3',myWord) >0,Locate('3',myWord),999),
    if (Locate('4',myWord) >0,Locate('4',myWord),999),
    if (Locate('5',myWord) >0,Locate('5',myWord),999),
    if (Locate('6',myWord) >0,Locate('6',myWord),999),
    if (Locate('7',myWord) >0,Locate('7',myWord),999),
    if (Locate('8',myWord) >0,Locate('8',myWord),999),
    if (Locate('9',myWord) >0,Locate('9',myWord),999)
  ) as myPos,
  if (LEAST (
    if (Locate('0',myWord) >0,Locate('0',myWord),999),
    if (Locate('1',myWord) >0,Locate('1',myWord),999),
    if (Locate('2',myWord) >0,Locate('2',myWord),999),
    if (Locate('3',myWord) >0,Locate('3',myWord),999),
    if (Locate('4',myWord) >0,Locate('4',myWord),999),
    if (Locate('5',myWord) >0,Locate('5',myWord),999),
    if (Locate('6',myWord) >0,Locate('6',myWord),999),
    if (Locate('7',myWord) >0,Locate('7',myWord),999),
    if (Locate('8',myWord) >0,Locate('8',myWord),999),
    if (Locate('9',myWord) >0,Locate('9',myWord),999)
  )=999,myWord,SUBSTR(myWord,1,LEAST (
    if (Locate('0',myWord) >0,Locate('0',myWord),999),
    if (Locate('1',myWord) >0,Locate('1',myWord),999),
    if (Locate('2',myWord) >0,Locate('2',myWord),999),
    if (Locate('3',myWord) >0,Locate('3',myWord),999),
    if (Locate('4',myWord) >0,Locate('4',myWord),999),
    if (Locate('5',myWord) >0,Locate('5',myWord),999),
    if (Locate('6',myWord) >0,Locate('6',myWord),999),
    if (Locate('7',myWord) >0,Locate('7',myWord),999),
    if (Locate('8',myWord) >0,Locate('8',myWord),999),
    if (Locate('9',myWord) >0,Locate('9',myWord),999)
  )-1)) as NewString
FROM myTable;

我的问题是

作为MyPos列船名后，为什么我不能在另一列使用该名称如下图所示的查询？

SELECT 
  myWord, 
  LEAST (
    if (Locate('0',myWord) >0,Locate('0',myWord),999),
    if (Locate('1',myWord) >0,Locate('1',myWord),999),
    if (Locate('2',myWord) >0,Locate('2',myWord),999),
    if (Locate('3',myWord) >0,Locate('3',myWord),999),
    if (Locate('4',myWord) >0,Locate('4',myWord),999),
    if (Locate('5',myWord) >0,Locate('5',myWord),999),
    if (Locate('6',myWord) >0,Locate('6',myWord),999),
    if (Locate('7',myWord) >0,Locate('7',myWord),999),
    if (Locate('8',myWord) >0,Locate('8',myWord),999),
    if (Locate('9',myWord) >0,Locate('9',myWord),999)
  ) as myPos,
  if (myPos=999,myWord,SUBSTR(myWord,1,myPos-1)) as NewString
FROM myTable;

但是，这给了我错误的

Unknown column 'myPos' in 'field list':

在这里看到更多的细节

请建议我可以做些什么，使这个查询使用别名短 。

Answer 1:

尝试把至少一部分作为子查询中。 你可以别名。

事情是这样的：

SELECT 
  mytable.myWord, 
  myPos.l,
  if (l=999,mytable.myWord,SUBSTR(mytable.myWord,1,l-1)) as NewString
FROM myTable, 
(select myword, LEAST (
    if (Locate('0',myWord) >0,Locate('0',myWord),999),
    if (Locate('1',myWord) >0,Locate('1',myWord),999),
    if (Locate('2',myWord) >0,Locate('2',myWord),999),
    if (Locate('3',myWord) >0,Locate('3',myWord),999),
    if (Locate('4',myWord) >0,Locate('4',myWord),999),
    if (Locate('5',myWord) >0,Locate('5',myWord),999),
    if (Locate('6',myWord) >0,Locate('6',myWord),999),
    if (Locate('7',myWord) >0,Locate('7',myWord),999),
    if (Locate('8',myWord) >0,Locate('8',myWord),999),
    if (Locate('9',myWord) >0,Locate('9',myWord),999)
  ) as l from mytable)
as myPos
where myPos.myword = mytable.myword

SQLFiddle例子

Answer 2:

基于@juergend答案，我也试图与下面及其工作过。

SELECT 
  t1.myWord, t2.l as MyPos, if (t2.l=999,t1.myWord,SUBSTR(t1.myWord,1,t2.l-1)) as NewString
FROM myTable t1 JOIN  
(select id, LEAST (
    if (Locate('0',myWord) >0,Locate('0',myWord),999),
    if (Locate('1',myWord) >0,Locate('1',myWord),999),
    if (Locate('2',myWord) >0,Locate('2',myWord),999),
    if (Locate('3',myWord) >0,Locate('3',myWord),999),
    if (Locate('4',myWord) >0,Locate('4',myWord),999),
    if (Locate('5',myWord) >0,Locate('5',myWord),999),
    if (Locate('6',myWord) >0,Locate('6',myWord),999),
    if (Locate('7',myWord) >0,Locate('7',myWord),999),
    if (Locate('8',myWord) >0,Locate('8',myWord),999),
    if (Locate('9',myWord) >0,Locate('9',myWord),999)
  ) as l from mytable) as t2
 ON t1.id=t2.id;

注意 ：对于这个我已经加入id表连接两张表。

演示

文章来源: Using alias name in another column