获取表中某字段的最大值并加1

获取表中某字段的最大值并加1，此字段可以为varchar。

SELECT IFNULL(MAX(CAST(某字段 AS UNSIGNED)),0) + 1 FROM 表

SELECT IFNULL(MAX(CAST(t.orgNo AS UNSIGNED)),0) AS orgNo FROM (SELECT SUBSTRING(ORG_NO,2) AS orgNo FROM SYS_ORG WHERE PARENT_NO = 'C1') t