I am trying to find the minimum length by getting the length of each values in a column (double) in a table and running a min function on top of it to get the minimum length.
This works well when the column is a string type but the 'length' function does not work for double datatype in impala, what is the other way to address this?
min(length(columnname))
All double columns are 8 bytes, as explained in the documentation. LENGTH() is a string function and it doesn't really make sense on a numeric value (although you can convert to a string and then measure the length).
Related
I am creating a table with several columns in sql:
CREATE TABLE.....
and one of them is going to have values like this: 675763582022462206:57. As you see it has : in it. So what is a type of it? Is it UInt16 or String?
It must be varchar or nvarchar in this case. The database doesn't recognize ":" as a part of a number, unless you say to Windows in advanced region settings that this is your decimal point. If you can store 57 (after ":") in a different column, then you can save the number before ":" as a bigint if you wish
This value can't be stored in a numeric type due to the colon (:), so you'll have to use one of the character types - i.e., a sufficiently long char or varchar.
The column type is nvarchar(200), but I get an error when I want to update a value with length of 99 characters. I found a lot of answers on the web, all of them saying "increase the column width", but as mentioned, it is already on 200 and I changed it to max, but still the same error. I am 100% sure I am using the correct database and correct column. Why is it not allowing me to add a string with length of 99 characters to a column with length of 200?
Screenshots:
Query:
Column property:
Query confirming column length
I am using the below query in SQL Server.
declare #dt float
set #dt = 1079938.05
select #dt AS Val,Convert(nvarchar(20),#dt) AS NVal, len(#dt) AS Len
Its output is
Val NVal Len
1079938.05 1.07994e+006 12
My questions are:
'Val' column shows right value.
'NVal' column shows strange value please explain us why it shows like this?
'Len' shows length and its actual length is 10 but it shows us 12. Please explain why it shows 12 instead of 10.
A float in sql server can be 4 or 8 byte. Find details.
LEN() is a function to measure the lenght of a string. So you want to measure the length of the string representation of the value, not the value itself.
The shown display value 1.07994e+006 is scientific notation and has 12 characters. Nothing wrong here.
Your call Convert(nvarchar(20),#dt) calls the CONVERT()-function with the defaul for FLOAT and REAL(Details and other formats here), which is scientific for numbers larger than 6 digits. The same happens implicitly when you call 'len(#dt)'. As the input of LEN() must be a string, the value is converted and then passed to the function.
What you can do:
You might think about a conversion to DECIMAL...
Another choice was first to use STR()-function together with RTRIM().
One more choice was FORMAT()-function (SQL Server 2012+)
.
Anyway you have to consider, that the text you see is not the real value.
LEN() works on [N]VARCHAR(), thus you're running into an implicit conversion from FLOAT to VARCHAR
see this: https://social.msdn.microsoft.com/Forums/sqlserver/en-US/a4ea2bc1-6f2f-4992-8132-f824fe4ffce0/length-of-float-values-in-ms-sql-server-gives-wrong-result?forum=transactsql
That means that LEN converts the value to VARCHAR before it actually calculates its length. That's because the length you get coincides with the length of your NVarChar value 1.07994e+006.
First of all: Don't use approximate data types when not forced to. A FLOAT is just an approximation, e.g. a simple value like 0.123 may be stored as 0.1230000000001 for instance. Use a precise type such as DECIMAL instead.
When converting a number to a string, you should usually specify a format as in format(#dt, '#,###,##0.00'). You don't do so, so it's up to the system what format to use. It uses a scientific notation 1.07994e+006 translating to 1.079940 x 10^6, which is approximately your number.
check:-
select #dt AS Val,Convert(nvarchar(20),#dt) AS NVal, len(CAST(CAST(#dt AS DECIMAL(20)) AS VARCHAR(20))) AS Len
I have method like this:
def self.weighted_average(column)
sql = "SUM(#{column} * market_cap) / SUM(market_cap) as weighted_average"
Company.select(sql).to_a.first.weighted_average
end
When the column is a decimal, it returns a value without problem.
But when the column is integer, the method ends up with a PG::NumericValueOutOfRange error.
Should I change column type integer to decimal, or is there a way to get the result of sum without changing column type?
You can always make float from your integer.
def self.weighted_average(column)
column = column.to_f
sql = "SUM(#{column} * market_cap) / SUM(market_cap) as weighted_average"
Company.select(sql).to_a.first.weighted_average
end
You can cast your value to alway be a decimal value, thus no need to change the column type:
sql = "SUM(#{column} * CAST(market_cap as decimal(53,8))) / SUM(CAST(market_cap as decimal(53,8))) as weighted_average"
P.S. I would go with changing the column type - it is consistent then.
I would suggest you to change the datatype to decimal. Because, when SUM gets PG::NumericValueOutOfRange, it means that your datatype is not sufficient. It will lead to gracefully handle this scenario, instead of a workaround.
Postgres documentation says this about SUM() return type:
bigint for smallint or int arguments, numeric for bigint arguments,
otherwise the same as the argument data type
This means that you will somehow need to change datatype that you pass to SUM. It can be one of the following:
Alter table to change column datatype.
Cast column to other datatype in your method.
Create a view that casts all integer columns to numeric and use that in your method.
You are trying to place a decimal value into a integer parameter. Unless you use the ABS() value that will not be possible, unless you are 100% sure that the % value will always be 0.
Use type Float or function ABS() if you HAVE to have an INT
Yo could try casting column to decimal
sql = "SUM(CAST(#{column}) AS DECIMAL * market_cap) / SUM(market_cap) as weighted_average"
I use Postgresql. I have a varchar column RAW_RET, mostly of numbers, and I'm trying to make a new column RET which is DOUBLE PRECISION. The problem is that a few rows of RAW_RET contain text, (Eg. character 'B' instead of numbers. Hence the following command:
update q_stock.daily set RET = cast(RAW_RET as double precision) ;
returns an error, invalid input syntax for type double precision: "B"
It seems like I need to do something like select only numeric rows, but I'm struggling at the moment to figure out how to do that...
For real numbers, you can use a regular expression:
update q_stock.daily
set RET = cast(RAW_RET as double precision)
where RAW_RET ~ '^[-]?[0-9]+\.?[0-9]*$';