分割SQL函数，计算字符串长度b/w 2和7逗号

⁠⁠⁠⁠⁠Suppose that I have string having comma between them and I want to find the length of string between 2nd to 7th comma or (n to n+). ⁠⁠⁠⁠⁠Suppose that I have string having comma be