获取mysql DB中列的最大值

Question

我的数据库表列值是

tenant_ id  group_id
2           2-100
2           2-111
1           1-222
1           1-888
2           2-999 
2           2-1000

查询：

select max(group_id) from prospect_group where tenant_id=2

我已经使用上面的查询来获取tenant_id = 2的最大值，但它返回的值为999而不是1000.如何获得1000作为最大值。??? 谁能帮我..？？？

Answer 1

您需要具有GROUP BY子句

SELECT tenant_ID, MAX(CAST(group_ID AS SIGNED))
FROM tableName
-- WHERE  tenant_id=2 -- uncomment this if you select only for specific tenant_ID
GROUP BY tenant_ID

通过替换为空char来尝试它。

SELECT tenant_ID, 
       MAX(CAST(REPLACE(group_ID, CONCAT(tenant_ID, '-'), '')  AS SIGNED)) maxGID
FROM tableName
-- WHERE  tenant_id=2 -- uncomment this if you select only for specific tenant_ID
GROUP BY tenant_ID

SQLFiddle演示

Answer 2

您需要添加GROUP BY子句。

select max(group_id) from prospect_group where tenant_id=2 group by tenant_ id