#mysql - Sun 18 Mar 2007 between 00:26 and 00:51



[1]StevenBaoHi, can someone tell me why the following sql query isn't working? Is it the syntax?
SELECT * FROM pages WHERE `fold1`='products' AND fold2=NULL ORDER BY pid DESC LIMIT 1
Yes, all these records exist
ToeBeewhen comparing to null you need the "IS" compare operator not =
fold2 IS null
[1]StevenBaoTHANK YOU ToeBee!
ToeBeealways beware of nulls. They can cause very unexpected results
doolsif i run this query: select MIN(score) from vpc_key_behaviour_cohort_score where core_behaviour_id = 4 and key_behaviour_id = 3;, i get the result: MIN(score) = 1.3999999761581 but when i run the query select * from vpc_key_behaviour_cohort_score where score = 1.3999999761581; i get an empty set... how can that be possible?
[RainMkr]LoL you used floats as a data type.
ToeBeeheh
dools[RainMkr]: yeah, is that a bad idea?
[RainMkr]well... what do you think? ;)
dools[RainMkr]: ... i think if i'm storing a float value that i should use a float datatype?
[RainMkr]dools: I think if you are going to use a float data type you should learn about floats
dools[RainMkr]: thanks for your input
ToeBeefloats suck if you need precision
there are always rounding issues
doolsToeBee: i don't need precision, just need something that won't kill a floating point value. i looked at the types and float seemd appropriate. decimal also looked appropriate. perhaps i should have used decimal
Xgcdools: Don't expect to check for equality using floats unless you're checking identity.
doolsXgc: what do you mean by 'checking identity'?
Xgcdools: WHERE t1.colx=t2.colx ... when colx contains a particular stored value.
dools: by identify I mean tests for self.
dools: or anything similar.
doolsXgc: ah okay. so not with something like 'where score < 2'; which is also not returning that particular row
(although it is returning things like 1.7 and 1.4)
Xgcdools: Once you have a stored value, you can check col1=col1 successfully. But you can't assume some constant 5.678 can equal any stored float value.
doolsXgc: right. yes it does seem like using float datatypes is a bad idea
Xgcdools: Not so much a bad idea, but you need to know how to use them properly.
doolsXgc: would you be able to give me an example of where you would use them to benefit if no comparison with constants work properly?
ToeBeedools: what happens when you do a select * from table where value = (select min(score) from table) ?
doolsToeBee: it returns two rows which have a score of 1.4 in them
ToeBee: if i change that to MIN then it prints out 1.3999999761581 so it's apparently using different precisions depending on whether i've called MIN or not
ToeBeewell it might just be a display issue
doolsToeBee: yes, i suppose it must be because even if i use MIN, but include other columns, it shows up as 1.4
Xgcdools: When you only care about testing or ordering by stored values or where inequalities are all you care about (f1 < f2) or (f1 < constant).
doolsXgc: right thanks
ToeBee: which is problematic because i really want to find out the primary keys of the row with that minimum score :P
Xgcdools: That's not a problem.
dools: The MIN(f1) will always match some specific f1.
dools: Apart from null.

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