mySQL:查找 VARCHAR 字段中字符串的重复项？

Question

我有一张这样的 table

TITLE          |   DESCRIPTION
------------------------------------------------
test1          |   value blah blah value
test2          |   value test
test3          |   test test test
test4          |   value test value test

如何仅选择包含后续冗余字符串的行(“blah blah”，而不是“blah bleh blah”)？

所需的输出应该只是

TITLE          |   DESCRIPTION
------------------------------------------------
test1          |   value blah blah value
test3          |   test test test

Answer 1

您可以针对此问题(以及许多其他问题)创建一个包含自然数的辅助表(仅一次)。它可用于多种用途:

create table seq (num int);
insert into seq values (1),(2),(3),(4),(5),(6),(7),(8);
insert into seq select num+8  from seq;
insert into seq select num+16 from seq;
insert into seq select num+32 from seq;
insert into seq select num+64 from seq;
/* continue doubling the number of records until you feel you have enough */

然后您可以在查询中联接该表，其中每个数字用作短语中单词的序列号。这样您就可以提取每个单词并将其与下一个进行比较:

select     title, description
from       phrases
where      description not in (
        select     description
        from       phrases p
        inner join seq 
                on seq.num <= length(p.description)
                            - length(replace(p.description,' ',''))
               and substring_index(substring_index(
                                   description, ' ', num), ' ', -1)
                   = substring_index(substring_index(
                                   description, ' ', num+1), ' ', -1)
        )

示例数据的输出为:

| title |           description |
|-------|-----------------------|
| test2 |            value test |
| test4 | value test value test |

SQL fiddle