PostgresQL 9.2 table query - underscores

Hello: My first post; a Postgres newbie ...

I am teaching myself PostgresQL using a trial database, and I am having trouble with underscores:

IN the following example,

development=# SELECT created_at, username FROM tweets;
created_at | username
-----------------------------------+-------------------
created_at | username
“Tue, 12 Feb 2013 08:43:09 +0000″ | “_DreamLead”
“Tue, 12 Feb 2013 07:31:06 +0000″ | “GunnarSvalander”
“Tue, 12 Feb 2013 07:30:24 +0000″ | “GEsoftware”
“Tue, 12 Feb 2013 06:58:22 +0000″ | “adrianburch”
“Tue, 12 Feb 2013 05:29:41 +0000″ | “AndyRyder5″
“Tue, 12 Feb 2013 05:24:17 +0000″ | “AndyRyder5″
“Tue, 12 Feb 2013 01:49:19 +0000″ | “Brett_Englebert”
“Tue, 12 Feb 2013 01:31:52 +0000″ | “Brett_Englebert”
“Mon, 11 Feb 2013 23:15:05 +0000″ | “NimbusData”
“Mon, 11 Feb 2013 22:15:37 +0000″ | “SSWUGorg”
(11 rows)

... why doesn't his work? :

development=# SELECT created_at, username FROM tweets WHERE username='_DreamLead';
created_at | username
------------+----------
(0 rows)

I understand why this works:

development=# SELECT created_at, username FROM tweets WHERE username LIKE '%_DreamLead%';
created_at | username
-----------------------------------+--------------
“Tue, 12 Feb 2013 08:43:09 +0000″ | “_DreamLead”
(1 row)

... but can't I tweak this,to work, somehow [without using the WHERE or SIMILAR TO clause(s)]? :

SELECT created_at, username FROM tweets WHERE username='_DreamLead';

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