PostgreSQL has a useful function called GREATEST. It returns the largest value of those passed to it as documented here.
Is there any equivalent in SQLite?
As a note, I only need it to work with 2 arguments.
SELECT MAX(1,2,..)
ref: https://sqlite.org/lang_corefunc.html#maxoreunc
max(X,Y,...)
The multi-argument max() function returns the argument with the maximum value, or return NULL if any argument is NULL. The multi-argument max() function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. If none of the arguments to max() define a collating function, then the BINARY collating function is used. Note that max() is a simple function when it has 2 or more arguments but operates as an aggregate function if given only a single argument.
using a second value in MAX(value1, value2) would be the equivalent
Example:
UPDATE products SET Quantity = MAX(Quantity - #value, 0)...
if (Quantity - value) return a "Negative Number -0" then Max( , 0) will return 0 because 0 is bigger than -0 / -1 / -2 ... and so on
Max( , 1) will return 1 if the same condition (Quantity - value) return 0 or a Negative Number .. etc, you get the idea !
if we assume that both Quantity and #value could be NULL then use the combination: IFNULL(MAX(Quantity-#value,0),0)
IFNULL(..., 0) will return the second value of your choice IF the first one is NULL
Related
In Oracle, any number divided by NULL returns NULL. I was wondering what is the case for DB2 Databases?
The whole point of it is to check whether the following expression behaves in the same way for Oracle and DB2:
SELECT a / NULLIF(b, 0) FROM some_table;
Say b=0, we would get a division by null.
The NULLIF function returns the null value if the two arguments are equal; otherwise, it returns the value of the first argument.
-NULLIF(expression,expression)-------------------------------
The result of using NULLIF(e1,e2) is the same as using the CASE expression:
CASE WHEN e1=e2 THEN NULL ELSE e1 END
Copy
When e1=e2 evaluates to unknown because one or both arguments is null, CASE expressions consider the evaluation not true. In this case, NULLIF returns the value
of the first argument.
IBM DB2 docs
So for DB2 and oracle it works same way
Db2 returns null when one of the operators in a math expression is null. For example
values (3 / cast(null as integer)) will return null.
On the other hand, the definition of NULLID is equal to that in Oracle. If both arguments are equal, it will return null.
I am selecting values from the database using Functions. I have three different functions in which if the first does not return anything I check for the second and third functions for values using NVL2. The problem is when I execute independent functions they return values but not in the NVL2 function My query is:
select NVL2(CRBP.FPDATE(LAM.ACID),
CRBP.FPDATE1(LAM.ACID),
CRBP.ODSANCDATE(GAM.ACID)) from
tbaadm.lam, TBAADM.GAM
where gam.acid = lam.acid
and gam.acid = 'VM12990'
This does not return any value.
But when I execute :
select CRBP.FPDATE (LAM.ACID) from tbaadm.lam where lam.acid = 'VM12990';
This Already returns a value. Shouldn't this be the value returned by my first query considering that it is the first in the check. What is the Problem with My first Query??
If CRBP.FPDATE returns a value the query should return the value returned by the function CRBP.FPDATE1 and if CRBP.FPDATE returns NULL then the query should return CRBP.ODSANCDATE's vlaue.
Does CRBP.FPDATE1 return anything?
NVL2(a,b,c) is a "if a is null then a else b" type function. so the value of a is never returned.
it sounds like you want COALESCE which will return the first not null value from the set of parameters
I'd like to perform division in a SELECT clause. When I join some tables and use aggregate function I often have either null or zero values as the dividers. As for now I only come up with this method of avoiding the division by zero and null values.
(CASE(COALESCE(COUNT(column_name),1)) WHEN 0 THEN 1
ELSE (COALESCE(COUNT(column_name),1)) END)
I wonder if there is a better way of doing this?
You can use NULLIF function e.g.
something/NULLIF(column_name,0)
If the value of column_name is 0 - result of entire expression will be NULL
Since count() never returns NULL (unlike other aggregate functions), you only have to catch the 0 case (which is the only problematic case anyway). So, your query simplified:
CASE count(column_name)
WHEN 0 THEN 1
ELSE count(column_name)
END
Or simpler, yet, with NULLIF(), like Yuriy provided.
Quoting the manual about aggregate functions:
It should be noted that except for count, these functions return a
null value when no rows are selected.
I realize this is an old question, but another solution would be to make use of the greatest function:
greatest( count(column_name), 1 ) -- NULL and 0 are valid argument values
Note:
My preference would be to either return a NULL, as in Erwin and Yuriy's answer, or to solve this logically by detecting the value is 0 before the division operation, and returning 0. Otherwise, the data may be misrepresented by using 1.
Another solution avoiding division by zero, replacing to 1
select column + (column = 0)::integer;
If you want the divider to be 1 when the count is zero:
count(column_name) + 1 * (count(column_name) = 0)::integer
The cast from true to integer is 1.
I am trying to create a score based on the char_length of a field. I am using a fraction of the char_length returned.
(CASE WHEN (char_length(e.summary)/100) is null THEN +0
ELSE +(char_length(e.summary)/100) END)
I would like to know how to set a maximum return value. Is there a simple function or do I need to do one more CASE WHEN with if >=10 THEN ... ?
Simplify to:
LEAST(COALESCE(length(e.summary)/100, 0), 10)
Use LEAST() to introduce an upper border as #Mark already mentioned.
Use COALESCE() to provide a default for NULL values.
length() does the same as char_length()
You can use the least function.
least(<YOUR CALC HERE>, 10) limits the maximum value returned to 10.
Is there a simple built in function in sql2000 that returns 0 or 0.00 if money or a float column is null? Or do I need to build the function myself, and how would I build it? if (isnull(col1)) then 0 else col1?
Yes, the function is called ISNULL, you use it like this:
SELECT ISNULL(columnname, 0.0) AS xyz FROM tablename
You basically specify which value to return in case the first value is null.
Note that ISNULL does not return a boolean value indicating whether the parameter is null or not, instead you pass it 2 parameters and it does the following:
If the first argument is non-null, return the value of the first argument
Otherwise, return the second argument
You can also use the COALESCE function for this, which takes an unspecified number of parameters, and returns the first non-null argument value back, in the order they're specified.
In other words:
ISNULL(columnname, 0.0)
and
COALESCE(columnname, 0.0)
behaves the same, but I don't know if there is a difference in "sargeability" of these two, ie. whether they can use indexes or not.