mysql - SQL从值创建列并填充其他列

Question

我想从 1 列中获取值，并将它们转换为另一列的标题。它更容易向您展示:

初始表:

Name      | Label   | Value
Tom Jones | January | 42
Rick James| March   | 83

结束表:

Name      | January | March
Tom Jones | 42      | NULL
Rick James| NULL    | 83

由于我在标签上进行的排序和排序类型，因此需要这样的格式。

更新: 当我提到多列值(value)时，我的意思是这样的:

Name      | Label_1   | ValueA_1 | ValueB_1 | Label_2 | ValueA_2 | ValueB_2
Tom Jones | January   | 42       | 77       | March   | 99       | 22
Rick James| March     | 83       | 17       | May     | NULL     | 112

Answer 1

使用 CREATE TABLE NewTable AS SELECT ...:

CREATE TABLE newTable
SELECT
  NAme, 
  SUM(CASE WHEN Label = 'January' THEN value  END) AS January,
  SUM(CASE WHEN Label = 'March' THEN value END) AS March
FROM tablename AS t1
GROUP BY Name;

这将创建一个全新的表 newTable，其结构与 SELECT 语句相同。

---

更新:

根据您的评论，如果您想获取逗号分隔的 value 的值:

CREATE TABLE newTable
SELECT
  Name, 
  GROUP_CONCAT(CASE WHEN Label = 'January' THEN value  END) AS January,
  GROUP_CONCAT(CASE WHEN Label = 'March' THEN value  END) AS March
FROM table1 AS t1
GROUP BY Name;

• SQL Fiddle Demo

---

更新:

如果您想动态执行此操作，而不是对值进行硬编码，则必须使用动态 sql 来执行此操作，如下所示:

SET @sql = NULL;

SELECT
  GROUP_CONCAT(DISTINCT CONCAT('GROUP_CONCAT(IF(Label = ''',
      Label, ''', value, NULL)) AS ', '''', Label , '''')
  ) INTO @sql
FROM Table1 ;

SET @sql = CONCAT('CREATE TABLE newTable ',
                  'SELECT Name,' ,
                  @sql, ' FROM table1 ',
                  ' GROUP BY Name');


prepare stmt 
FROM @sql;

execute stmt;

Updated SQL Fiddle Demo