Question

I need to run dynamically constructed queries against Informix IDS 9.x; while WHERE clause is mostly quite simple, Projection clause can be quite complicated with lots of columns and formulas applied to columns. Here is one example:

SELECT ((((table.I_ACDTIME + table.I_ACWTIME + table.I_DA_ACDTIME + table.I_DA_ACWTIME +
           table.I_RINGTIME))+(table.I_ACDOTHERTIME + table.I_ACDAUXINTIME + 
           table.I_ACDAUX_OUTTIME)+(table.I_TAUXTIME + table.I_TAVAILTIME + 
           table.I_TOTHERTIME)+((table.I_AVAILTIME + table.I_AUXTIME)*
         ((table.MAX_TOT_PERCENTS/100)/table.MAXSTAFFED)))/(table.INTRVL*60))
FROM table
WHERE ...

The problem arises when some of the fields used contain zeroes; Informix predictably throws division by zero error, but the error message is not very helpful:

DBD::Informix::st fetchrow_arrayref failed:
SQL: -1202: An attempt was made to divide by zero.

In this case, it is desirable to return NULL upon failed calculation. Is there any way to achieve this other than parse Projection clause and enclose each and every division attempt in CASE … END? I would prefer to use some DBD::Informix magic if it’s there.

Answer 1

I don’t believe you’ll be able to solve this with DBD::Informix or any other database client, without resorting to parsing the SQL and rewriting it. There’s no option to just ignore the column with the /0 arithmetic: the whole statement fails when the error is encountered, at the engine level.

If it’s any help, you can write the code to avoid /0 as a DECODE rather than CASE ... END, which is a little cleaner, ie:

DECODE(table.MAXSTAFFED, 0, NULL,
  ((table.MAX_TOT_PERCENTS/100)/table.MAXSTAFFED)))/(table.INTRVL*60)))