<p>我正在使用以下表来存储产品数据：</p> <pre class="brush:php;toolbar:false;">mysql> SELECT * FROM product; +---------------+---------------+--------+ | id | name | description | stock | +---------------+---------------+--------+ | 1 | product1 | first product | 5 | | 2 | product2 | second product| 5 | +---------------+---------------+--------+ mysql> SELECT * FROM product_additional; +-----------------+------------+ | id | fieldname | fieldvalue | +-----------------+------------+ | 1 | size | S | | 1 | height | 103 | | 2 | size | L | | 2 | height | 13 | | 2 | color | black | +-----------------+------------+</pre> <p>使用以下查询从两个表中选择记录：</p> <pre class="brush:php;toolbar:false;">mysql> SELECT p.id , p.name , p.description ,MAX(IF(pa.fieldname = 'size', pa.fieldvalue, NULL)) as `size` ,MAX(IF(pa.fieldname = 'height', pa.fieldvalue, NULL)) as `height` ,MAX(IF(pa.fieldname = 'color', pa.fieldvalue, NULL)) as `color` FROM product p LEFT JOIN product_additional AS pa ON p.id = pa.id GROUP BY p.id +---------------+---------------+--------+---------+--------+ | id | name | description | size | height | color | +---------------+---------------+--------+---------+--------+ | 1 | product1 | first product | S | 103 | null | | 2 | product2 | second product| L | 13 | black | +---------------+---------------+--------+---------+--------+</pre> <p>一切都正常工作 :) </p> <p>因为我动态填充“additional”表，所以如果查询也是动态的就好了。这样我就不必每次输入新的字段名和字段值时都要更改查询。</p>

SET @sql = '';
SELECT
    @sql := CONCAT(@sql,if(@sql='','',', '),temp.output)
FROM
(
    SELECT
      DISTINCT
        CONCAT(
         'MAX(IF(pa.fieldname = ''',
          fieldname,
          ''', pa.fieldvalue, NULL)) AS ',
          fieldname
        ) as output
    FROM
        product_additional
) as temp;

SET @sql = CONCAT('SELECT p.id
                    , p.name
                    , p.description, ', @sql, ' 
                   FROM product p
                   LEFT JOIN product_additional AS pa 
                    ON p.id = pa.id
                   GROUP BY p.id, p.name, p.description');

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

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(IF(pa.fieldname = ''',
      fieldname,
      ''', pa.fieldvalue, NULL)) AS ',
      fieldname
    )
  ) INTO @sql
FROM product_additional;

SET @sql = CONCAT('SELECT p.id
                    , p.name
                    , p.description, ', @sql, ' 
                   FROM product p
                   LEFT JOIN product_additional AS pa 
                    ON p.id = pa.id
                   GROUP BY p.id, p.name, p.description');

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