Having long strings in MySql stored procedures - mysql

Question

Is there a way of enabling a long strings to be put onto multiple lines so that when viewed on screen or printed the code is easier to read?
Perhaps I could be clearer.
Have a stored procedure with lines like
IF ((select post_code REGEXP '^([A-PR-UWYZ][A-HK-Y]{0,1}[0-9]{1,2} [0-9][ABD-HJLNP-UW-Z]{2})|([A-PR-UWYZ][0-9][A-HJKMPR-Y] [0-9][ABD-HJLNP-UW-Z]{2})|([A-PR-UWYZ][A-HK-Y][0-9][ABEHMNPRV-Y]) [0-9][ABD-HJLNP-UW-Z]{2})$') = 0)
Would like to be able to modify the string so that I can view it within 80 character width. Anybody got any ideas of how to do this.
PS: It is the regular expression for UK postcodes

Answer 1

For example,
-- a very long string in one block
set my_str = 'aaaabbbbcccc';
can be also written as
-- a very long string, as a concatenation of smaller parts
set my_str = 'aaaa' 'bbbb' 'cccc';
or even better
-- a very long string in a readable format
set my_str = 'aaaa'
'bbbb'
'cccc';
Note how the spaces and end of line between the a/b/c parts are not part of the string itself, because of the placement of quotes.
Also note that the string data here is concatenated by the parser, not at query execution time.
Writing something like:
-- this is broken
set my_str = 'aaaa
bbbb
cccc';
produces a different result.
See also
http://dev.mysql.com/doc/refman/5.6/en/string-literals.html
Look for "Quoted strings placed next to each other are concatenated to a single string"

Answer 2

You could split it up into the front and back components of the postcode and then dump the whole lot into a UDF.
This will keep the ugliness in one place and means you'll only have to make changes to one block of code when/if Royal Mail decide to change the format of UK postcodes ;-)
Something like this should do the trick:
DELIMITER $$
CREATE FUNCTION `isValidUKPostcode`(candidate varchar(255)) RETURNS BOOLEAN READS SQL DATA
BEGIN
declare back varchar(3);
declare front varchar(10);
declare v_out boolean;
set back = substr(candidate,-3);
set front = substr(candidate,1,length(candidate)-3);
set v_out = false;
IF (back REGEXP '^[0-9][ABD-HJLNP-UW-Z]{2}$'= 1) THEN
CASE
WHEN front REGEXP '^[A-PR-UWYZ][A-HK-Y]{0,1}[0-9]{1,2} $' = 1 THEN set v_out = true;
WHEN front REGEXP '^[A-PR-UWYZ][0-9][A-HJKMPR-Y] $' = 1 THEN set v_out = true;
WHEN front REGEXP '^[A-PR-UWYZ][A-HK-Y][0-9][ABEHMNPRV-Y] $' = 1 THEN set v_out = true;
END CASE;
END IF;
return v_out;
END