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Archive-name: databases/sybase-faq/part13
URL: http://www.isug.com/Sybase_FAQ
Version: 1.7
Maintainer: David Owen
Last-modified: 2003/01/17
Posting-Frequency: posted every 3rd month
   A how-to-find-the-FAQ article is posted on the intervening months.

                                 SQL Advanced                                  
                                                                               
 

    6.2.1    How to emulate the Oracle decode function/crosstab
    6.2.2    How to implement if-then-else within a select-clause.
    6.2.3    deleted due to copyright hassles with the publisher
    6.2.4    How to pad with leading zeros an int or smallint.
    6.2.5    Divide by zero and nulls.
    6.2.6    Convert months to financial months.
    6.2.7    Hierarchy traversal - BOMs.
    6.2.8    Is it possible to call a UNIX command from within a stored
    procedure or a trigger?
    6.2.9    Information on Identities and Rolling your own Sequential Keys
    6.2.10  How can I execute dynamic SQL with ASE
    6.2.11  Is it possible to concatenate all the values from a column and
    return a single row?
    6.2.12  Selecting rows N to M without Oracle's rownum?
    6.2.13  How can I return number of rows that are returned from a grouped
    query without using a temporary table?
   
Useful SQL Tricks SQL Fundamentals ASE FAQ

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6.2.1: How to emulate the Oracle decode function/crosstab

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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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6.2.2: How to implement if-then-else in a select clause

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ASE 11.5 introduced the case statement, which can be used to replace a lot of
this 'trick' SQL with more readable (and standard) code. With a case statement,
an if then else is as easy as:

declare @val char(20)
select @val = 'grand'

select case when @val = 'small' then
                'petit'
            else
                'grand'
            end

However, quite a number of people are still using pre-11.5 implementations,
including those people using the free 11.0.3.3 Linux release. In that case you
can use the following recipe.

To implement the following condition in a select clause:

if @val = 'small' then
    print 'petit'
else
    print 'grand'
fi

in versions of ASE prior to 11.5 do the following:

select isnull(substring('petit', charindex('small', @val), 255), 'grand')

To test it out, try this:

declare @val char(20)
select @val = 'grand'
select isnull(substring('petit', charindex('small', @val), 255), 'grand') 

This code is not readily understandable by most programmers, so remember to
comment it well.

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6.2.3: Removed

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6.2.4: How to pad with leading zeros an int or smallint.

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By example:

declare @Integer        int

/* Good for positive numbers only. */
select @Integer = 1000

select "Positives Only" =
       right( replicate("0", 12) + convert(varchar, @Integer), 12)

/* Good for positive and negative numbers. */
select @Integer = -1000

select "Both Signs" =
       substring( "- +", (sign(@Integer) + 2), 1) +
       right( replicate("0", 12) + convert(varchar, abs(@Integer)), 12)

select @Integer = 1000

select "Both Signs" =
       substring( "- +", (sign(@Integer) + 2), 1) +
       right( replicate("0", 12) + convert(varchar, abs(@Integer)), 12)

go

Produces the following results:

 Positives Only
 --------------
 000000001000

 Both Signs
 -------------
 -000000001000

 Both Signs
 -------------
 +000000001000

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6.2.5: Divide by zero and nulls

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During processing, if a divide by zero error occurs you will not get the answer
you want. If you want the result set to come back and null to be displayed
where divide by zero occurs do the following:

1> select * from total_temp
2> go
 field1      field2
 ----------- -----------
          10          10
          10           0
          10        NULL

(3 rows affected)
1> select field1, field1/(field2*convert(int,
                  substring('1',1,abs(sign(field2))))) from total_temp
2> go
 field1
 ----------- -----------
          10           1
          10        NULL
          10        NULL

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6.2.6: Convert months to financial months

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To convert months to financial year months (i.e. July = 1, Dec = 6, Jan = 7,
June = 12 )

Method #1

select ... ((sign(sign((datepart(month,GetDate())-6) * -1)+1) *
   (datepart(month, GetDate())+6))
      + (sign(sign(datepart(month, GetDate())-7)+1) *
   (datepart(month, GetDate())-6)))
   ...
  from ...

Method #2

select charindex(datename(month,getdate()),
"          July      August    September October   November  December
January   Febuary   March     April     May       June      "
                     ) / 10

In the above example, the embedded blanks are significant.

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-- 

- David Alex Lamb, one of the *.answers moderators
[email protected]

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