Re: how to escape _ in select

On 7/28/2010 12:35 PM, Wes James wrote:
> I'm trying to do this:
>
> select * from table where field::text ilike '%\_%';
>
> but it doesn't work.
>
> How do you escape the _ and $ chars?
>
> The docs say to use \, but that isn't working.
>
> ( http://www.postgresql.org/docs/8.3/static/functions-matching.html )
>
> The text between '%...%' can be longer, I'm just trying to figure out
> how to escape some things.  I've found that ' works with '' and \
> works with \\
>

Instead of escaping how about looking at double $ quoting.

http://www.postgresql.org/docs/8.4/static/sql-syntax-lexical.html

4.1.2.4. Dollar-Quoted String Constants

While the standard syntax for specifying string constants is usually
convenient, it can be difficult to understand when the desired string
contains many single quotes or backslashes, since each of those must be
doubled. To allow more readable queries in such situations, PostgreSQL
provides another way, called "dollar quoting", to write string
constants. A dollar-quoted string constant consists of a dollar sign
($), an optional "tag" of zero or more characters, another dollar sign,
an arbitrary sequence of characters that makes up the string content, a
dollar sign, the same tag that began this dollar quote, and a dollar
sign. For example, here are two different ways to specify the string
"Dianne's horse" using dollar quoting:

$$Dianne's horse$$
$SomeTag$Dianne's horse$SomeTag$

Notice that inside the dollar-quoted string, single quotes can be used
without needing to be escaped. Indeed, no characters inside a
dollar-quoted string are ever escaped: the string content is always
written literally. Backslashes are not special, and neither are dollar
signs, unless they are part of a sequence matching the opening tag.

It is possible to nest dollar-quoted string constants by choosing
different tags at each nesting level. This is most commonly used in
writing function definitions. For example:

$function$
BEGIN
     RETURN ($1 ~ $q$[\t\r\n\v\\]$q$);
END;
$function$

Here, the sequence $q$[\t\r\n\v\\]$q$ represents a dollar-quoted literal
string [\t\r\n\v\\], which will be recognized when the function body is
executed by PostgreSQL. But since the sequence does not match the outer
dollar quoting delimiter $function$, it is just some more characters
within the constant so far as the outer string is concerned.

The tag, if any, of a dollar-quoted string follows the same rules as an
unquoted identifier, except that it cannot contain a dollar sign. Tags
are case sensitive, so $tag$String content$tag$ is correct, but
$TAG$String content$tag$ is not.

A dollar-quoted string that follows a keyword or identifier must be
separated from it by whitespace; otherwise the dollar quoting delimiter
would be taken as part of the preceding identifier.

Dollar quoting is not part of the SQL standard, but it is often a more
convenient way to write complicated string literals than the
standard-compliant single quote syntax. It is particularly useful when
representing string constants inside other constants, as is often needed
in procedural function definitions. With single-quote syntax, each
backslash in the above example would have to be written as four
backslashes, which would be reduced to two backslashes in parsing the
original string constant, and then to one when the inner string constant
is re-parsed during function execution.




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