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How to emulate the Oracle decode function/crosstab in Sybase
If you are using ASE version 11.5 or later, the simplest way to implement the Oracle decode is with the CASE statement. The following code snippet should be compared with the example using a characteristic function given below .
SELECT STUDENT_ID,
(CASE WHEN COURSE_ID = 101 THEN 1 ELSE 0 END) AS COURSE_101,
(CASE WHEN COURSE_ID = 105 THEN 1 ELSE 0 END) AS COURSE_105,
(CASE WHEN COURSE_ID = 201 THEN 1 ELSE 0 END) AS COURSE_201,
(CASE WHEN COURSE_ID = 210 THEN 1 ELSE 0 END) AS COURSE_210,
(CASE WHEN COURSE_ID = 300 THEN 1 ELSE 0 END) AS COURSE_300
GROUP BY STUDENT_ID
ORDER BY STUDENT_ID
However, if you have a version of ASE that does not support the case statement, then you will have to try the following. There may be other reasons to try characteristics functions. If you go to the Amazon web site and look for reviews for of Rozenshteins book, Advanced SQL, you will see that one reviewer believes that a true crosstab is not possible with the case statement. I am not sure. I have also not done any performance tests to see which is quicker.
There is a neat way to use boolean logic to perform cross-tab or rotation queries easily, and very efficiently. Using the aggregate 'Group By' clause in a query and the ISNULL(), SIGN(), ABS(), SUBSTRING() and CHARINDEX() functions, you can create queries and views to perform all kinds of summarizations.
This technique does not produce easily understood SQL statements.
If you want to test a field to see if it is equal to a value, say 100, use the following code:
SELECT (1- ABS( SIGN( ISNULL( 100 - <field>, 1))))
The innermost function will return 1 when the field is null, a positive value if the field < 100, a negative value if the field is > 100 and will return 0 if the field = 100. This example is for Sybase or Microsoft SQL server, but other servers should support most of these functions or the COALESCE() function, which is the ANSI equivalent to ISNULL.
The SIGN() function returns zero for a zero value, -1 for a negative value, 1 for a positive value The ABS() function returns zero for a zero value, and > 1 for any non-zero value. In this case it will return 0 or 1 since the argument is the function SIGN(), thus acting as a binary switch.
Put it all together and you get '0' if the value match, and '1' if they don't. This is not that useful, so we subtract this return value from '1' to invert it, giving us a TRUE value of '1' and a false value of '0'. These return values can then be multiplied by the value of another column, or used within the parameters of another function like SUBSTRING() to return a conditional text value.
For example, to create a grid from a student registration table containing STUDENT_ID and COURSE_ID columns, where there are 5 courses (101, 105, 201, 210, 300) use the following query:
Compare this version with the case statement above.
SELECT STUDENT_ID,
(1- ABS( SIGN( ISNULL( 101 - COURSE_ID, 1)))) COURSE_101,
(1- ABS( SIGN( ISNULL( 105 - COURSE_ID, 1)))) COURSE_105,
(1- ABS( SIGN( ISNULL( 201 - COURSE_ID, 1)))) COURSE_201,
(1- ABS( SIGN( ISNULL( 210 - COURSE_ID, 1)))) COURSE_210,
(1- ABS( SIGN( ISNULL( 300 - COURSE_ID, 1)))) COURSE_300
GROUP BY STUDENT_ID
ORDER BY STUDENT_ID
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