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Preface: That's one of the SQL pitfalls I've stumbeld over too often...

Well, sometimes I've to turn expressions from an ordinary programming language into a SQL query, and sometimes these expressions contain the classical scalar max() function, say like "where max(expr1, expr2) > 0".

The following (absolutely senseless) query would be a sample:

select * from systab
where max(table_page_count, ext_page_count) > 10;

Of course, using max() that way in a SQL query is doomed to fail, as MAX() is an aggregate function and works on rows of data, not on two (or more) separate expressions, so this raises

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Question: Is there a way to use max() as intended here?

asked 18 Mar '13, 17:04

Volker%20Barth's gravatar image

Volker Barth
accept rate: 34%

edited 18 Mar '13, 17:13

Well, you cannot use MAX() for that - but of course SQL Anywhere has according support:

Use GREATER() as a scalar MAX() and LESSER() as a scalar MIN(), such as

select * from systab
where greater(table_page_count, ext_page_count) > 10

And now I hope I won't forget that anymore:)

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answered 18 Mar '13, 17:10

Volker%20Barth's gravatar image

Volker Barth
accept rate: 34%

edited 18 Mar '13, 17:11


Thanks for the votes: You like to learn from my mistakes, don't you:)

Feel free to tell about your favourite pitfallslearning experiences, too...

(19 Mar '13, 12:47) Volker Barth

It should be noted that GREATER() and LESSER() are vendor extensions (as documented), so for portable SQL, one would probably need to

  • use a CASE expression ("case when isnull(table_page_count, 0) > isnull(ext_page_count, 0) then ...") or
  • try to re-state the logic by ORing expressions or the like.

Aside: I had thought of suggesting an IF expression here - but that's another one of these very helpful vendor extension itself:)

(21 Mar '13, 06:44) Volker Barth
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question asked: 18 Mar '13, 17:04

question was seen: 3,197 times

last updated: 21 Mar '13, 06:44