Mysql 选择每组一列的最大值

我想显示

porcentaje

列的值，但仅显示id最高的记录（每个

项

）：

输出：

item                       id     porcentaje
--------------------------------------------
EXCAVACION DE FUNDACION    90     100
EXCAVACION DE FUNDACION    91     50
HORMIGON FUNDACIONES       92     90
HORMIGON FUNDACIONES       93     40

我只想显示标记的记录：

item                       id     porcentaje
--------------------------------------------
EXCAVACION DE FUNDACION    90     100
EXCAVACION DE FUNDACION    91     50 <------
HORMIGON FUNDACIONES       92     90
HORMIGON FUNDACIONES       93     40 <------

---

您应该按项目分组，然后可以使用

group_concat

，它有一个

order by

子句，然后从中提取第一个值：

SELECT     tb_avance.item, 
           max(tb_avance.id) as id,
           cast(group_concat(tb_proceso.porcentaje order by id desc) as unsigned) 
              as porcentaje
FROM       tb_avance_detalle
INNER JOIN tb_avance on tb_avance_detalle.id_avance = tb_avance.id
INNER JOIN tb_proceso ON tb_proceso.id_avance_detalle = tb_avance_detalle.id
INNER JOIN tb_mapa ON tb_mapa.id = tb_avance_detalle.id_mapa
WHERE      tb_mapa.manzana = 107 
       AND tb_mapa.lote = 12
GROUP BY   tb_avance.item

看见

item                       id     porcentaje
--------------------------------------------
EXCAVACION DE FUNDACION    91     50
HORMIGON FUNDACIONES       93     40

SELECT     tb_avance.item, 
           max(tb_avance.id) as id,
           cast(group_concat(tb_proceso.porcentaje order by id desc) as unsigned) 
              as porcentaje
FROM       tb_avance_detalle
INNER JOIN tb_avance on tb_avance_detalle.id_avance = tb_avance.id
INNER JOIN tb_proceso ON tb_proceso.id_avance_detalle = tb_avance_detalle.id
INNER JOIN tb_mapa ON tb_mapa.id = tb_avance_detalle.id_mapa
WHERE      tb_mapa.manzana = 107 
       AND tb_mapa.lote = 12
GROUP BY   tb_avance.item