如何从字段mysql中选择前20个字符之后的字符

 select address (first 20 character) as Address1 , 
        address (characters after first 20 if less then 20 then NULL) as Address2
 from customer

如何选择20个字符之后的字符串？

要获取前 20 个字符之后的字符（请注意，如果不足 20 个字符，该函数将返回空字符串）：

SELECT SUBSTRING('Some Random Address That is Longer than 20 characters' FROM 20);

现在，如果您需要地址 2 为 NULL，请首先检查字符长度：

SELECT if(char_length(address) > 20, SUBSTRING(address FROM 20), NULL);

要获取前 20 个字符，您可以使用 substring 函数，如下所示：

SELECT SUBSTRING('Some Random Address', 1, 20);

现在最终的查询可能如下所示：

SELECT SUBSTRING(address, 1, 20) as Address1, 
    IF(CHAR_LENGTH(address) > 20, SUBSTRING(address FROM 20), NULL) as Address2
FROM customer