Pattern matching with identical wildcards

问题

I'm working with PostgreSQL and want to know whether you can have a wildcard retain its value.

So for example say I had

select * from tableOne where field like ‘_DEF_’;

Is there a way to get the first and last wildcard to be the exact same character?

So an example matching result could be: ADEFA or ZDEFZ.

回答1:

You can use a regular expression with a back-reference:

select * 
from some_table
where some_column ~* '^(.)DEF(\1)$'

^(.)DEF(\1)$ means: some character at the beginning followed DEF followed by the first character must occur at the end of the string.

The () defines a group and the \1 references the first group (which is the first character in the input sequence in this example)

SQLFiddle example: http://sqlfiddle.com/#!15/d4c4d/1

回答2:

Use regular expression:

with test as (
    select 'xABa' as foo
    union select 'xABx'
    union select 'xJBx'
)
select * from test
where foo ~* E'^(.)AB\\1$'

Outputs:

 foo  
------
 xABx
(1 row)

来源：https://stackoverflow.com/questions/29033022/pattern-matching-with-identical-wildcards