Just need your help here.
I have a table T
A (nvarchar) B()
--------------------------
'abcd'
'xyzxcz'
B should output length of entries in A for which I did
UPDATE T
SET B = LEN(A) -- I know LEN function returns int
But when I checked out the datatype of B using sp_help T, it showed column B as nvarchar.
What's going on ?
select A
from T
where B > 100
also returned correct output?
Why is nvarchar working with logical operators ?
Please help.
Check https://learn.microsoft.com/en-us/sql/t-sql/data-types/data-type-conversion-database-engine?view=sql-server-2017 where it is said that data types are converted explicitly or implicitly when you move, compare or store a variable. In your case, you are comparing column B with 100, forcing sql server to implicitly convert it to integer type (check the picture about conversions on the same page). As a prove, try to alter a row putting some text in column B and, after repeating your select query B>100, sql server will throw a conversione error trying to obtain an integer out of your text.
It works because of implicit conversion between types.
Data type precedence
When an operator combines expressions of different data types, the data type with the lower precedence is first converted to the data type with the higher precedence. If the conversion isn't a supported implicit conversion, an error is returned.
Types precedence:
16. int
...
25. nvarchar (including nvarchar(max) )
In you example:
select A
from T
where B > 100
--nvarchar and int (B is implicitly casted to INT)
when adding a column to a table in ssms, not adding a datatype a "default" datatype is chosen. for me on 2017 developer it's nchar(10). if you want it to be int define the column with datatype of int. in tsql it'd be
create table T (
A nvarchar --for me the nvarchar without a size gives an nvarchar(2)
,B int
);
sp_help T
--to make a specific size, largest for nvarchar is 4000 or max...max is the replacement for ntext of old, as.
create table Tmax (
A nvarchar(max)
,B int
);
--understanding nvarchar and varchar for len() and datalength()
select
datalength(N'wibble') datalength_nvarchar -- nvarchar is unicode and uses 2 bytes per char, so 12
,datalength('wibble') datalength_varchar -- varchar uses 1 byte per so 6
,len(N'wibble') len_nvarchar -- count of chars, so 6
,len('wibble') len_varchar -- count of char so still 6
nvarchar(max) and varchar(max)
hope this helps, the question is a bit discombobulated
Related
How come string can contain integer. Even if I assume string storing numeric values as string, but even i can use in it calculation and getting the result as well. Just to try I wrote 5 in inverted commas and still calculation works fine. Not sure how?
declare #x varchar(20)
declare #y int
select #x='5'
select #y=6
select #x+#y
SQL Server -- and all other databases -- convert values among types when the need arises.
In this case, you have + which can be either string concatenation or number addition. Because one argument is an integer, it is interpreted as addition, and SQL Server attempts to convert the string to a number.
If the string cannot be converted, then you will get an error.
I would advise you to do your best to avoid such implicit conversions. Use the correct type when defining values. If you need to store other types in a string, use cast()/convert() . . . or better yet, try_cast()/try_convert():
try_convert(int, #x) + #y
A varchar can contain any character from the collations codepage you are using. For the purposes of this answer, I'm going to assume you're using something like the collation SQL_Latin1_General_CP1_CI_AS (which doesn't have any "international" characters, like Kanji, Hiragana, etc).
You first declare the variable #x as a varchar(20) and put the varchar value '5' in it. This is not an int, it's a varchar. This is an important distinction as a varchar and a numerical data type (like an int) behave very differently. For example '10' has a lower value than '2', where as the opposite is true for 10 and 2. (This is one reason why using the correct data type is always important.)
Then the second variable you have is #y, which is an int and has the value 6.
Then you have your expression SELECT #x+#y;. This has 2 parts to it. Firstly, as you have 2 datatypes, Data Type Precedence comes into play. int has a higher precedence than a varchar, and so #x is implicitly converted to an int. Then the expression is calculated, uses + as an addition operator (not a concatenation operator). Therefore the expression is effectively derived like this:
#x + #y = '5' + 6 = CONVERT(int,'5') + 6 = 5 + 6 = 11
SQL Server uses the following precedence order for data types:
user-defined data types (highest)
sql_variant
xml
datetimeoffset
datetime2
datetime
smalldatetime
date
time
float
real
decimal
money
smallmoney
bigint
int
smallint
tinyint
bit
ntext
text
image
timestamp
uniqueidentifier
nvarchar (including nvarchar(max) )
nchar
varchar (including varchar(max) )
char
varbinary (including varbinary(max) )
binary (lowest)
I'm trying to filter some data - I have a column which looks like it is mainly smallint/int. Is there anyway I can run a where statement to say where not int or where not small int??
Microsoft SQL Server manager.
If you want a where clause that can tell you if the column contain information that can't be converted to int or smallint, you can use try_cast:
SELECT *
FROM <TableName>
WHERE TRY_CAST(<ColumnName> AS Int) IS NULL
You can change the int to smallint to get values that can't be converted to smallint but might be convertible to int.
Don't forget to replace <TableName> and <ColumnName> to the names of the relevant table and column.
The Try_Cast built in function will return null if the value in <ColumnName> is null or if it can't be converted to int (and since all smallint values can also be converted to int, it also can't be converted to smallint).
If in a SELECT statement there is the following line:
iif(fr.BoundID=0,'OutBound','InBound') as 'FlightBound'
Then when I perform a CREATE TABLE statement, should I include the actual datatype of the BoundID field which is a tinyint in the database table, or shall the datatype be varchar because I think (but not 100% sure looking at the existing code) that the previous person writing this code is saying display 'OutBound, InBound' if the ID is 0?
In your case it will be VARCHAR(8). You can always check metadata using sys.dm_exec_describe_first_result_set:
SELECT *
FROM sys.dm_exec_describe_first_result_set(
'SELECT iif(BoundID=0,''OutBound'',''InBound'') as ''FlightBound''
FROM #tab',NULL,0)
LiveDemo
What datatype to choose for new table TINYINT vs Textual representation is dependent on your business requirements. I would probably stay with TINYINT (search for lookup table named like BoundType or ask senior developer/architect).
The return type is the type in true_value and false_value with the highest precendence (reference, see return types)
Returns the data type with the highest precedence from the types in true_value and false_value. For more information, see Data Type Precedence (Transact-SQL).
Data type precendence here up to SQL Server 2016:
user-defined data types (highest)
sql_variant
xml
datetimeoffset
datetime2
datetime
smalldatetime
date
time
float
real
decimal
money
smallmoney
bigint
int
smallint
tinyint
bit
ntext
text
image
timestamp
uniqueidentifier
nvarchar (including nvarchar(max) )
nchar
varchar (including varchar(max) )
char
varbinary (including varbinary(max) )
binary (lowest)
Recently I was Playing with SQL Server data types, and a Large number of data in the table and trying to figure out the Performance with Varchar and Numeric data. But, I got some error which I don't think should not have been but it is. My problem is below :
I have a table :
create table sa(f1 varchar(100))
I have a Stored Procedure that Inserts 100000 data into the table :
create proc sad
as
begin
declare #i int=0
while #i<100000
begin
insert into sa values(#i)
set #i=#i+1
end
end
exec sad
And I have tested the following:
select CONVERT(int,f1) from sa //Works Fine, i tested after the Problem
select sum(convert(int,f1)) from sa //Didn't Worked, So i tested above and Below
select sum(convert(decimal(18,2),f1)) from sa //And, it again works fine
But, When I sum Converting F1 to Int, it shows me an error.
But, when I only select Converting to Int it's fine.
And, when I sum Converting F1 to decimal it works Fine.
What is the SUM function data type?
On the Above data, it works well with Decimal but not Int?
Why?
I'm Getting the Following error
Arithmetic overflow error converting expression to data type int.
You're summing as INT which has a range that cannot hold that sum.
The DECIMAL can.
The sum of all values from 1 up to 99999 is 4999950000, the maximum INT value is 2147483647, less than half of what the sum ends up as.
When you sum INT's, you're getting a new INT. When you're summing DECIMAL's, you're getting a new DECIMAL, so the input type defines the output type.
You can switch to using bigint instead, and it should "be fine".
Also, on a second note, please don't store numbers as text!
According to MS documentation (see https://learn.microsoft.com/en-us/sql/t-sql/functions/sum-transact-sql), the SUM() function returns values of a different type, according to the datatype of the column you are adding: if the column is of type int, tinyint, or smallint, then SUM returns values of type int.
Converting to bigint or decimal makes SUM() return a larger datatype, this explains why in that case you have no overflow.
Expect you have exceeded the maximum int value that SQL Server allows (2,147,483,647) - see https://learn.microsoft.com/en-us/sql/t-sql/data-types/int-bigint-smallint-and-tinyint-transact-sql.
Decimal allows a far higher limit of up to 10^38 - 1 (i.e. 1 with 38 zeros after) - see https://learn.microsoft.com/en-us/sql/t-sql/data-types/decimal-and-numeric-transact-sql.
However, if the values are of type int, I wouldn't recommend converting to decimal. Decimal values are useful when you have figures with possible numbers after the decimal place with a known precision and scale (e.g. for currency, percentages etc.) As another poster has suggested, the best conversion here would be to a bigint:
select sum(cast(f1 as bigint)) from sa
Looks like your resulting sum is too big for int, use bigint, also check int, bigint, smallint, and tinyint (Transact-SQL)
select sum(convert(bigint,f1)) from sa
Try this:
CONVERT(NUMERIC(18,2),SUM(0))
Please suppose that in SQL Server 2005, if you launch the following query:
SELECT CHICKEN_CODE FROM ALL_CHICKENS WHERE MY_PARAMETER = 'N123123123';
you obtain:
31
as result.
Now, I would like to write a function that, given a value for MY_PARAMETER, yields the corresponding value of CHICKEN_CODE, found in the table ALL_CHICKENS.
I have written the following stored function in SQL Server 2005:
ALTER FUNCTION [dbo].[determines_chicken_code]
(
#input_parameter VARCHAR
)
RETURNS varchar
AS
BEGIN
DECLARE #myresult varchar
SELECT #myresult = CHICKEN_CODE
FROM dbo.ALL_CHICKENS
WHERE MY_PARAMETER = #input_parameter
RETURN #myresult
END
But if I launch the following query:
SELECT DBO.determines_chicken_code('N123123123')
it yields:
NULL
Why?
Thank you in advance for your kind cooperation.
define the length of your varchar variables like this
varchar(100)
Without the 100 (or whatever length you choose) its lengh is 1 and the where clause will filter out the correct results.
Specify a length for your varchar (ex.: varchar(100)). Without length, varchar = 1 char.
As per other PS, You can store only one char in the #myresult because you have not specified any length, bcoz 1 char length is default for Varchar datatype.
Why we are getting NUll, not the first char:
If there are multiple records are filtered on basis of Where clause in ALL_CHICKENS table then the value of CHICKEN_CODE column is picked up from last row in ALL_CHICKENS table.
It seems that the last row has null value in CHICKEN_CODE column.
Specify a length for #input_parameter, #myresult as by default varchar lengh is 1.