最近用到城市矩阵相关 需要将城市与城市距离转化为二维表 通过动态SQL直接实现 贴出来一起学习：

表就三个字段，包含在sql内。

SET @sql:='';SELECT @sql:=GROUP_CONCAT(item) FROM(SELECT CONCAT(@sql,'SUM(IF(to_city=\'',to_city,'\'',',distance,0)) AS \'',to_city,'\'') itemFROM (SELECT cm.to_city FROM `cities_matrix`  cm  GROUP BY cm.to_city ORDER BY cm.to_city)a)a;SET @sql:=CONCAT('SELECT cm.from_city,',@sql,' FROM cities_matrix cm GROUP BY cm.from_city'); PREPARE stmt FROM @sql;  EXECUTE stmt;