We are using NHibernate over SQL Server and SQLite.
The database stores records in rows rather than columns -- each row having Path|Value as columns. Path and Value are both string properties.
For certain values of Path we would like to query for inequalities -- greater-than, less-than, etc.
The trouble we are having is that because the properties are strings, the inequalities are using string comparisons -- for example, searching for Value >= 18 returns rows where Value = 5. Unfortunately we are having trouble working around this.
1) This restriction produces incorrect results (saying 18 < 5):
Restrictions.Ge("Value", item.Value);
2) We tried casting the value to an integer, but this code produces a SqlException from NHibernate -- Error converting data type nvarchar to bigint.
Restrictions.Le(Projections.Cast(NHibernateUtil.Int64, Projections.Property("SearchString")), item.Value)
3) We were looking for a way to pad the property value with zeros (so that we would get 018 > 005), but could not find a way to do this in NHibernate.
Does anyone have any advice?
Thank you in advance!
Assuming that you want to compare on integer value, with IQueryOver:
1) This restriction produces incorrect results (saying 18 < 5):
Restrictions.Ge("Value", item.Value);
Restrictions.Ge
(
Projections.Cast(NHibernateUtil.Int32, Projections.Property<YourEntity>(x => x.YourProperty))
, intValue
)
Convert your datatype accordingly. If your C# datatype (intValue) is already numeric, no need to convert it. If your x.YourProperty is already numeric type, no need to convert it. Adjust above code accordingly.
2) We tried casting the value to an integer, but this code produces a SqlException from NHibernate -- Error converting data type nvarchar to bigint.
Restrictions.Le(Projections.Cast(NHibernateUtil.Int64, Projections.Property("SearchString")), item.Value)
Refer the above and check the datatype of item.Value.
Related
I wanted to return a value formatted with commas at every thousand if a number or just the value if it wasn't a number
I used the following statement which returned the error:
Conversion failed when converting the nvarchar value '1,000' to data type int.
Declare #QuantityToDelete int = 1000
SELECT CASE
WHEN ISNUMERIC(#QuantityToDelete)=1
THEN format(cast(#QuantityToDelete as int),'N0')
ELSE #QuantityToDelete
END [Result]
I can get it to work by using the following
SELECT CASE
WHEN ISNUMERIC(#QuantityToDelete)=1
THEN format(cast(#QuantityToDelete as int),'N0')
ELSE cast(#QuantityToDelete as varchar)
END [Result]
Result=1,000
Why doesn't the first example work when the ELSE #QuantityToDelete part of the statement isn't returned?
If I use the below switching the logic condition
SELECT CASE
WHEN ISNUMERIC(#QuantityToDelete)=0
THEN format(cast(#QuantityToDelete as int),'N0')
ELSE #QuantityToDelete
END [Result]
Result=1000
Which is expected, but no error, the case statement still has unmatched return types an nvarchar and an int as in the first example just different logic?
The important point to note is that a case expression returns a single scalar value, and that value has a single data type.
A case expression is fixed, it must evaluate the same and work the same for that query at runtime no matter what data flows through the query - in other words, the result of the case expression cannot be an int for some rows and a string for others.
Remember that the result of a query can be thought of, and used as, a table - so just like a table where you you define a column as being a specific data type, you cannot have a column where the data type can be different for rows of data.
Therefore with a case expression, SQL Server must determine at compile time what the resulting data type will be, which it does (if necessary) using data type precedence. If the case expression has different data types returned in different execution paths then it will attempt to implicitly cast them to the type with the highest precedence.
Hence your case expression that attempts to return two different data types fails because it's trying to return both a nvarchar and int and SQL Server is implicitly casting the nvarchar value to an int - and failing.
The second one works because you are controlling the casting and both paths result in the same varchar data type which works fine.
Also note that when defining a varchar it's good practice to define its length also, you can easily get complacent as it works here because the default length is 30 when casting however the default is 1 otherwise.
See the relevant part of the documentation
This has been bothering me with my coding continuously and I can't seem to google a good workaround.
I have a number of columns which are data type nvarchar(255). Pretty standard I would assume.
Anyway, I want to run:
DELETE FROM Ranks WHERE ISNULL(INST,0) = 0
where INST is nvarchar(255). I am thrown the error:
Conversion failed when converting the nvarchar value 'Un' to data type int.
which is the first non null in the column. However, I don't care for this showing me the error means it's not null? - I just want to delete the nulls!
Is there something simple I'm missing.
Any help would be fab!
An expression may only be of one type.
Expression ISNULL(INST,0) involves two source types, nvarchar(255) and int. However, no type change happens at this point, because ISNULL is documented to return the type of its first argument (nvarchar), and will convert the second argument to that type if needed, so the entire original expression is equivalent to ISNULL(INST, '0').
Next step is the comparison expression, ISNULL(INST, '0') = 0. It again has nvarchar(255) and int as the source data types, but this time nothing can stop the conversion - in fact, it must happen for the comparison operator, =, to even work. According to the data type precedence list, the int wins, and is chosen as the resulting type of the comparison expression. Hence all values from column INST must be converted to int before the comparison = 0 is made.
If you
just want to delete the nulls
, then just delete the nulls:
DELETE FROM Ranks WHERE INST IS NULL
If for some reason you absolutely have to use isnull in this fashion, which there is no real reason for, then you should have stayed in the realm of strings:
DELETE FROM Ranks WHERE ISNULL(INST, '') = ''
That would have deleted null entries and entries with empty strings (''), just like the WHERE ISNULL(INST, 0) = 0 would have deleted null entries and entries with '0's if all values in INST could have been converted to int.
With ISNULL(INST,0) you are saying: If the string INST is null, replace it with the string 0. But 0 isn't a string, so this makes no sense.
With WHERE ISNULL(INST,0) = 0 you'd access all rows where INST is either NULL or 0 (but as mentioned a string is not an integer).
So what do you want to achieve? Delete all rows where INST is null? That would be
DELETE FROM ranks WHERE inst IS NULL;
I have a nvarchar column in one of my tables that I have imported from Access. I am trying to change to an int. To move to a new table.
The original query:
insert into members_exams_answer
select
ua.members_exams_id, ua.exams_questions_id,
ua.members_exams_answers_value, ua.members_exams_answers_timestamp
from
members_exams as me
full join
UserAnswers1 as ua on me.members_exams_username = ua.members_exams_id
full join
exams_questions as eq on eq.exams_questions_id = ua.exams_questions_id
This throws an error:
Conversion failed when converting the nvarchar value 'AAAR78509883' to data type int.
I have tired:
select convert (int, UserAnswers1.members_exams_id)
from UserAnswers1
and
select cast(members_exams_id as integer) int_members_exams_id
from UserAnswers1
and
select cast (members_exams_id as int)
from UserAnswers1
All result in the same error
Conversion failed when converting the nvarchar value 'AAAR78509883' to data type int.
Clearly you are trying to convert data that is alphanumeric to an int and that cannot be done.
Looking at your data why are you insisting on converting it to an int when it cannot be an int? Why not just process it as an nvarchar?
Your problem could be systemic where all data has a leading alpha characters that you need to strip out (and hopefully the same number of alpha characters)
In that case use a substring to strip off the alphas (this assumes the name number of alphabetic characters in each record). Or use a varchar or nvarchar field instead of an int. If the number of leading characters varies or if they can be leading or trailing or some other combination, it will much more complex to fix than we can probably describe on the Internet.
The other possibility is that you simply have some bad data. In which case identify the records which are not numeric and fix them or null the value out if they cannot be fixed. This happens frequently when you have stored the data in an incorrect datatype.
SELECT logicalTime, traceValue, unitType, entName
FROM vwSimProjAgentTrace
WHERE valueType = 10
AND agentName ='AtisMesafesi'
AND ( entName = 'Hawk-1')
AND simName IN ('TipSenaryo1_0')
AND logicalTime IN (
SELECT logicalTime
FROM vwSimProjAgentTrace
WHERE valueType = 10 AND agentName ='AtisIrtifasi'
AND ( entName = 'Hawk-1')
AND simName IN ('TipSenaryo1_0')
AND CONVERT(FLOAT , traceValue) > 123
) ORDER BY simName, logicalTime
This is my sql command and table is a view table...
each time i put "convert(float...) part " i get
Msg 8114, Level 16, State 5, Line 1
Error converting data type nvarchar to float.
this error...
One (or more) of the rows has data in the traceValue field that cannot be converted to a float.
Make sure you've used the right combination of dots and commas to signal floating point values, as well as making sure you don't have pure invalid data (text for instance) in that field.
You can try this SQL to find the invalid rows, but there might be cases it won't handle:
SELECT * FROM vwSimProjAgentTrace WHERE NOT ISNUMERIC(traceValue)
You can find the documentation of ISNUMERIC here.
If you look in BoL (books online) at the convert command, you see that a nvarchar conversion to float is an implicit conversion. This means that only "float"-able values can be converted into a float. So, every numeric value (that is within the float range) can be converted. A non-numeric value can not be converted, which is quite logical.
Probably you have some non numeric values in your column. You might see them when you run your query without the convert. Look for something like comma vs dot. In a test scenario a comma instead of a dot gave me some problems.
For an example of isnumeric, look at this sqlfiddle
This was my Interview Question
there are two columns called Length and Breadth in Area table
Length Breadth Length*Breadth
20 NULL ?
30 ?
21.2 1 ?
I tried running the same question on MYSQL while inserting,To insert an empty value I tried the below query . Am I missing anything while inserting empty values in MYSQL.
insert into test.new_table values (30,);
Answers: With Null,Result is Null.
With float and int multiplication result is float
As per your question the expected results would be as below.
SELECT LENGTH,BREADTH,LENGTH*BREADTH AS CALC_AREA FROM AREA;
LENGTH BREADTH CALC_AREA
20
30 0 0
21.2 1 21.2
For any(first) record in SQL SERVER if you do computation with NULL the answer would be NULL.
For any(second) record in SQL SERVER, if you do product computation between a non-empty value and an empty value the result would be zero as empty value is treated as zero.
For any(third) record in SQL SERVER, if you do computation between two non-empty data type values the answer would be a NON-EMPTY value.
Check SQL Fiddle for reference - http://sqlfiddle.com/#!3/f250a/1
That blank Breath (second row) cannot happen unless Breath is VARCHAR. Assuming that, the answers will be:
NULL (since NULL times anything is NULL)
Throws error (since an empty string is not a number. In Sql Server, the error is "Error converting data type varchar to numeric.")
21.20 (since in Sql Server, for example, conversion to a numeric type is automatic, so SELECT 21.2 * '1' returns 21.20).
Assuming that Length and Breadth are numerical types of some kind the second record does not contain possible values — Breadth must be either 0 or NULL.
In any event, any mathematical operation in SQL involving a NULL value will return the value NULL, indicating that the expression cannot be evaluated. The answer are NULL, impossible, and 21.2.
The product of any value and NULL is NULL. This is called "NULL propagation" if you want to Google it. To score points in an interview, you might want to mention that NULL isn't a value; it's a special marker.
The fact that the column Breadth has one entry "NULL" and one entry that's blank (on the second row) is misleading. A numeric column that doesn't have a value in a particular row means that row is NULL. So the second column should also show "NULL".
The answer to the third row, 21.2 * 1, depends on the data type of the column "Length*Breadth". If it's a data type like float, double, or numberic(16,2), the answer is 21.2. If it's an integer column (integer, long, etc.), the answer is 21.
A more snarky answer might be "There's no answer. The string "Length*Breadth" isn't a legal SQL column name."
In standard SQL they would all generate errors because you are comparing values (or nulls) of different types:
CAST ( 20 AS FLOAT ) * CAST ( NULL AS INTEGER ) -- mismatched types error
CAST ( '' AS INTEGER ) -- type conversion error
CAST ( AS INTEGER ) -- type conversion error
CAST ( 21.2 AS FLOAT ) * CAST ( 2 AS INTEGER ) -- mismatched types error
On the other hand, most SQL product would implicitly cast values when comparing values (or nulls) of different types according to type precedence e.g. comparing float value to an integer value would in effect cast the integer to float and result in a float. At the product level, the most interesting question is what happens when you compare a null of type integer with a value (or even a null) of type float...
...but, frankly, not terribly interesting. In an interview you are presented with a framework (in the form of questions asked of you) on which to present your knowledge, skills and experience. The 'answer' here is to discuss nulls (e.g. point out that nulls are tricky to define and behave in unintuitive ways, which leads to frequent bugs and a desire to avoid nulls entirely, etc) and whether implicit casting is a good thing.