如何選擇字段後的前20個字符mysql

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個字符後選擇字符串？

Answer 1

爲了得到第20個字符後面的字符（注意，如果沒有二十個字符，函數將返回一個空字符串）：

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

現在，如果您需要解決2爲NULL，你檢查字符長度第一：

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

爲了得到第20個字符，你可以使用子功能是這樣的：

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

現在

最終的查詢看起來是這樣的：

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

Answer 2

的substring就是你要找的內容：

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