PostgreSQL: Regular Expression Query

Taken from PostgreSQL Introduction & Concepts

regular expression: ~
regular expression (case-insensitive): ~*
not equal to regular expression: !~
not equal to regular expression (case-insensitive): !~*

Basic Rules:

start: ^
end: $
any single character: .
set of characters: [abc]
set of characters not equal: [^abc]
range of characters: [a-z]
range of characters not equal: [^a-z]
zero or 1: ?
zero or more: *
one or more: +
OR: |

Examples:

begins with D: ~ '^D'
contains D: ~ 'D'
D in second position: ~ '^.D'
begins with D and contains e: ~ 'D.*e'
begins with D, contains e, then f: ~ '^D.*e.*f'
contains A, B, C, or D: ~ '[A-D]' or ~ '[ABCD]'
contains A or a: ~ * 'a' or ~ '[Aa]'
does not contain D: !~ 'D'
does not begin with D: !~ '^D' or ~ '^[^D]'
begin with D, one optional space in front: ~ '^ ?D'
begin with D, with optional leading spaces: ~ '^ *D'
begin with D, with at least 1 space: ~ '^ +D'
end with G, with optional trailing spaces: ~ 'G *$'