Question

我的疑问：

  set @sql = NULL;
select
  group_concat(distinct
    concat(
   'max(if(first.study = ''',
  study, ''', first.avg_scores, NULL)) as ',
  study
)
  ) into @sql
from `table`;

SET @sql = concat('select first.name,
              ', @sql, ' 
               from `table` first
                 join `table` second
                   on first.name = second.name
               group by first.name');

prepare stmt from @sql;
execute stmt;
deallocate prepare stmt;

当列＃34;研究＆＃34;

中的数据时

=================================
  name  |  study  |  avg_scores
=================================
  alfa      c         75
  beta      c         70
  alfa     php        85
  beta     php        90

和结果：它是真的。

===========================
  name   |   c   |  php
===========================
  alfa      75      85
  beta      70      90

当我在表格中有数据时出现问题：

===================================
  name  |  study     |  avg_scores
===================================
  alfa    junior c         75
  beta    junior c         70
  alfa    junior php       85
  beta    junior php       90

错误：＆＃34;您的SQL语法有错误;查看与MySQL服务器版本对应的手册正确的语法使用近＆c; c，max（if（first.study =＆＃39; junior php＆＃39;， first.avg_scores，NULL））作为初级php＆＃39;在第2行：从@sql＆＃34;

准备stmt

所以：如何修复我的查询？

Answer 1

问题是您需要转义标识符，因为列名不能有空格。以下使用名称的双引号（您也可以使用反引号）：

set @sql = NULL;
select group_concat(distinct concat('max(if(first.study = ''', study,
                                    ''', first.avg_scores, NULL)) as "', study, '"'
---------------------------------------------------------------------^ ----------^    
                                   )
                   ) into @sql
from `table`;

SET @sql = concat('select first.name, ', @sql, '
                   from `table` first join `table` second on first.name = second.name
                   group by first.name');

查询枢轴，带有两个单词，列中有空格

1 个答案: