string - Postgres : limit length of returned string but needs to end on a full word

Question

对于 Postgres，我试图在返回字符串之前截断它，以便我可以在客户端的部分结果列表中显示它。关键是它需要以一个完整的词结尾。我已经做到了: SELECT comments, substr(comments, 1, 80) AS "trunc"FROM book; 下一步是否是使用 RegEx 对子字符串进行子字符串处理(可能试图确保字符串以 a 结尾)空间)？

Answer 1

使用substring(string from pattern) . 12 个字符的示例:

with the_data(comments) as (
    values
        ('follow me'::text),
        ('abcdef ghijkl'),
        ('abcd efgh ijkl'),
        ('abc def ghi jkl'),
        ('ab cd ef gh ij kl')
    )

select substring(left(comments || ' ', 12) from '.*\s')
from the_data;

  substring   
--------------
 follow me 
 abcdef 
 abcd efgh 
 abc def ghi 
 ab cd ef gh 
(5 rows)