mysql - 如何从字段mysql中选择前20个字符后的字符

Question

 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 个字符后的字符串？

Answer 1

获取前20个字符之后的字符(注意，如果没有20个字符，该函数将返回一个空字符串):

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

现在如果你需要地址 2 为 NULL，你首先检查字符长度:

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

要获取前 20 个字符，可以像这样使用 substring 函数:

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

现在最终的查询看起来像这样:

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