mysql - function like isnull() to check for zero-value

Question

I'm looking for a function to check if a column has the value 0 that behaves like the isnull() function.

This is what I've got so far:

CONCAT(
    SUBSTRING_INDEX(
        SUBSTRING(textCol, 1, 
            LOCATE(DATE_FORMAT(dateCol,'%d.%m.%Y  %H:%i'), textCol)-1),
            '|',
             -1),       
    SUBSTRING(
        textCol,
        LOCATE(DATE_FORMAT(dateCol,'%d.%m.%Y  %H:%i'), textCol),
        IFNULL(
            LOCATE( /* this will return 0 if it's the last entry */
                '|', 
                textCol, 
                LOCATE(DATE_FORMAT(dateCol,'%d.%m.%Y  %H:%i'), textCol)
            ) - LOCATE(DATE_FORMAT(dateCol,'%d.%m.%Y  %H:%i'), textCol),
            LENGTH(textCol))))

The data in textCol is sort of like a CSV-file with another CSV-file inside each column. Each dataset is delimited by | while each dataset inside that is delimited by &&. The inner fields are name, date like '%d.%m.%Y %H:%i' and a comment.

i want to extract the dataset that corresponds to a certain DATETIME I've got in dateCol. The problem is that if the one I'm looking for is the last entry in textCol, the LOCATE (see comment) returns 0. But that breaks my SUBSTRING so only the first half of the entry is returned.

I added a ISNULL(), which of course doesn't do anything here. What I would like to do is have something similar to the ISNULL() that sort of does a ISZERO(), much like the || operator in Perl behaves.

There might be an alltogether better way to achieve what I want. Please don't hesitate to tell me.

Answer 1

Might be useful here: there is a funky way to check if expression is either NULL or 0:

IFNULL(NULLIF(expr, 0), alt_expr)

This returns alt_expr if expr is NULL or 0, otherwise returns expr.

Answer 2

This is shorter and avoids repeating expression:

SELECT COALESCE( NULLIF( expression, 0 ), 'a substitute for zero' ) FROM mytable