如何从字段mysql中的前20个字符后选择字符

Question

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

如何在20个字符后选择字符串？

Answer 1

获取前20个字符后的字符（请注意，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，如果您需要地址2为NULL，则首先检查字符长度：

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

要获取前20个字符，可以使用子字符串函数，如下所示：

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

现在最终查询可能如下所示：

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

Answer 2

您正在寻找substring：

SELECT SUBSTRING(address, 1, 20) AS Address1, 
       SUBSTRING(address FROM 20) AS Address2
FROM   customer