当行是动态-MYSQL时，将行转换为列

Question

我想将行转换为列，行数是动态的。 我已经检查了一些问题，他们使用静态值在mysql中使用CASE。就我而言，价值观将是动态的。这是我的结构：

我将以where meeting_id=1的形式查询表格，我试图得到这样的输出：

meeting_id, first_name, last_name, occupation
         1, danyal    , sandeelo , engineer

Answer 1

您可以使用GROUP_CONCAT和Prepared statements来处理MySQL Pivot中的动态字段数。

请在下面查询一些测试数据。

  

准备数据

CREATE TABLE Meeting
(
    ID INT,
    Meeting_id INT,
    field_key VARCHAR(100),
    field_value VARCHAR(100)
);

INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (1, 1,'first_name' , 'danyal');
INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (2, 1,'last_name' , 'sandeelo');
INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (3, 1,'occupation' , 'engineer');
INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (4,2,'first_name' , 'John');
INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (5,2,'last_name' , 'Matthew');
INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (6,2,'occupation' , 'engineer');
INSERT INTO Meeting(ID,Meeting_id,field_key,field_value)
VALUES (7,2,'field4' , 'xyz');

  

SQL查询

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'max(case when field_key = ''',
      field_key,
      ''' then field_value end) ',
      field_key
    )
  ) INTO @sql
FROM
  Meeting;
SET @sql = CONCAT('SELECT Meeting_id, ', @sql, ' 
                  FROM Meeting 
                   GROUP BY Meeting_id');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;