I am having a column named DP as shown:
07-APR-2011
12-APR-2011
26-APR-2011
Now to retrieve the query for selecting the payments made in the month of april i came across a query
select * from payments where instr(dp,'APR')<>0
Okay , i am well acquainted with INSTR function and > sign , but cant interpret the logic with<> sign here !
[UPDATE]
i am also aware that <> is equivalent of != .
But my point is we could have used
instr(dp,'APR') instead of doing instr(dp,'APR')<>0
<> means "is not equal to". You can also write !=, if you prefer.
instr(dp,'APR') returns zero if 'APR' is not a substring of dp, so instr(dp,'APR')<>0 means "'APR' is a substring of dp". It could also be written as dp LIKE '%APR%'.
Update for updated question:
But my point is we could have used instr(dp,'APR') instead of doing instr(dp,'APR')<>0
No, you couldn't have. Some dialects of SQL treat zero as "false" and other integers as "true", but Oracle does not do this. It treats integers and Booleans as separate types, and does not implicitly convert between them. WHERE 0 is not a valid WHERE-clause.
<> is Not Equals - basically it's checking that a substring of 'APR' appears in the string.
If that function returned 0 then it would indicate 'APR' does not appear anywhere in the string to be searched.
Related
I am tasked with doing a SQL coalesce on DEA and NPI numbers in order to return the available value, there will be no cases where both DEA and NPI values are available for a Dr. This is what I am currently using in my script:
coalesce(nullif(convert(varchar,NationalProviderIdentifier),'0'), DEANumber) as 'DrID'
Unknown values can be defined as having the following values:
"Unknown"
0
0000000000
"blank"
I will need to provide a hover over the Dr. id value that will either say "DEA Number" or "NPI Number" depending on what is being displayed. I have written the following VB code for the ToolTip expression and it works fine:
=IIF(Fields!DrID.Value = "Unknown" or Fields!DrID.Value = "" or Fields!DrID.Value = "0000000000", "DEA/NPI Unavailable",
IIF(Len(Fields!DrID.Value) > 9, "NPI", "DEA"))
There will be cases when both DEA and NPI number are unknown, which is what I am checking for in the first IIF section of the VB. The second IFF statement is determining whether the value being returned is an NPI (10 digits long) or DEA (9 digits long) number.
I was advised to make my VB less complex by using a SQL function. I have not written a whole lot of functions and I am not not sure how to proceed. I assume that I will not reference the function in the Visual Studio but somewhere in the main dataset that retrieves the DrID data field?
Well the simple way would be to add an additional column to your SQL query, like so (assumes that NationalProviderIdentifier is an INT and that neither allows NULLs):
CASE WHEN NationalProviderIdentifier <> 0 THEN 'NPI'
WHEN DEANumber IN('Unknown','','0000000000') THEN 'N/A'
ELSE 'DEA' END as 'DrIdSrc'
I need to checking a column where numeric or not in SQL Server 2012.
This my case code.
CASE
WHEN ISNUMERIC(CUST_TELE) = 1
THEN CUST_TELE
ELSE NULL
END AS CUSTOMER_CONTACT_NO
But when the '78603D99' value is reached, it returns 1 which means SQL Server considered this string as numeric.
Why is that?
How to avoid this kind of issues?
Unfortunately, the ISNUMERIC() function in SQL Server has many quirks. It's not exactly buggy, but it rarely does what people expect it to when they first use it.
However, since you're using SQL Server 2012 you can use the TRY_PARSE() function which will do what you want.
This returns NULL:
SELECT TRY_PARSE('7860D399' AS int)
This returns 7860399
SELECT TRY_PARSE('7860399' AS int)
https://msdn.microsoft.com/en-us/library/hh213126.aspx
Obviously, this works for datatypes other than INT as well. You say you want to check that a value is numeric, but I think you mean INT.
Although try_convert() or try_parse() works for a built-in type, it might not do exactly what you want. For instance, it might allow decimal points, negative signs, and limit the length of digits.
Also, isnumeric() is going to recognize negative numbers, decimals, and exponential notation.
If you want to test a string only for digits, then you can use not like logic:
(CASE WHEN CUST_TELE NOT LIKE '%[^0-9]%'
THEN CUST_TELE
END) AS CUSTOMER_CONTACT_NO
This simply says that CUST_TELE contains no characters that are not digits.
Nothing substantive to add but a couple warnings.
1) ISNUMERIC() won't catch blanks but they will break numeric conversions.
2) If there is a single non-numeric character in the field and you use REPLACE to get rid of it you still need to handle the blank (usually with a CASE statement).
For instance if the field contains a single '-' character and you use this:
cast(REPLACE(myField, '-', '') as decimal(20,4)) myNumField
it will fail and you'll need to use something like this:
CASE WHEN myField IN ('','-') THEN NULL ELSE cast(REPLACE(myField, '-', '') as decimal(20,4)) END myNumField
All,
I'm writing a query that includes a CASE statement which compares two datetime fields. If Date B is > Date A, then I'd like the query to display Date B. However, if Date B is not > Date A, then the user who will be getting the report created by the query wants the column to be blank (in other words, not contain the word 'NULL', not contain a hyphen, not contain a low values date). I've been researching this today but have not come up with a viable solution so thought I'd ask here. This is what I have currently:
CASE
WHEN B.DTE_LNP_LAST > A.DTE_PROC_ACT
THEN B.DTE_LNP_LAST
ELSE ?
END AS "DATE OF DISCONNECT"
If I put NULL where the ? is, then I get a hyphen (-) in my query result. If I omit the Else statement, I also get a hyphen in the query result. ' ' doesn't work at all. Does anyone have any thoughts?
Typically the way nulls are displayed is controlled by the client software used to display query results. If you insist on doing that in SQL, you will need to convert the date to a character string:
CASE
WHEN B.DTE_LNP_LAST > A.DTE_PROC_ACT
THEN VARCHAR_FORMAT(B.DTE_LNP_LAST)
ELSE ''
END AS "DATE OF DISCONNECT"
Replace VARCHAR_FORMAT() with the formatting function available in your DB2 version on your platform, if necessary.
You can use the coalesce function
Coalesce (column, 'text')
If the first value is null, it will be replaced by the second one.
I just had a trivial but genuine use for NULLIF(), for the first time in my career in SQL. Is it a widely used tool I've just ignored, or a nearly-forgotten quirk of SQL? It's present in all major database implementations.
If anyone needs a refresher, NULLIF(A, B) returns the first value, unless it's equal to the second in which case it returns NULL. It is equivalent to this CASE statement:
CASE WHEN A <> B OR B IS NULL THEN A END
or, in C-style syntax:
A == B || A == null ? null : A
So far the only non-trivial example I've found is to exclude a specific value from an aggregate function:
SELECT COUNT(NULLIF(Comment, 'Downvoted'))
This has the limitation of only allowing one to skip a single value; a CASE, while more verbose, would let you use an expression.
For the record, the use I found was to suppress the value of a "most recent change" column if it was equal to the first change:
SELECT Record, FirstChange, NULLIF(LatestChange, FirstChange) AS LatestChange
This was useful only in that it reduced visual clutter for human consumers.
I rather think that
NULLIF(A, B)
is syntactic sugar for
CASE WHEN A = B THEN NULL ELSE A END
But you are correct: it is mere syntactic sugar to aid the human reader.
I often use it where I need to avoid the Division by Zero exception:
SELECT
COALESCE(Expression1 / NULLIF(Expression2, 0), 0) AS Result
FROM …
Three years later, I found a material use for NULLIF: using NULLIF(Field, '') translates empty strings into NULL, for equivalence with Oracle's peculiar idea about what "NULL" represents.
NULLIF is handy when you're working with legacy data that contains a mixture of null values and empty strings.
Example:
SELECT(COALESCE(NULLIF(firstColumn, ''), secondColumn) FROM table WHERE this = that
SUM and COUNT have the behavior of turning nulls into zeros. I could see NULLIF being handy when you want to undo that behavior. If fact this came up in a recent answer I provided. If I had remembered NULLIF I probably would have written the following
SELECT student,
NULLIF(coursecount,0) as courseCount
FROM (SELECT cs.student,
COUNT(os.course) coursecount
FROM #CURRENTSCHOOL cs
LEFT JOIN #OTHERSCHOOLS os
ON cs.student = os.student
AND cs.school <> os.school
GROUP BY cs.student) t
I have the following SQL query:
select AuditStatusId
from dbo.ABC_AuditStatus
where coalesce(AuditFrequency, 0) <> 0
I'm struggling a bit to understand it. It looks pretty simple, and I know what the coalesce operator does (more or less), but dont' seem to get the MEANING.
Without knowing anymore information except the query above, what do you think it means?
select AuditStatusId
from dbo.ABC_AuditStatus
where AuditFrequency <> 0 and AuditFrequency is not null
Note that the use of Coalesce means that it will not be possible to use an index properly to satisfy this query.
COALESCE is the ANSI standard function to deal with NULL values, by returning the first non-NULL value based on the comma delimited list. This:
WHERE COALESCE(AuditFrequency, 0) != 0
..means that if the AuditFrequency column is NULL, convert the value to be zero instead. Otherwise, the AuditFrequency value is returned.
Since the comparison is to not return rows where the AuditFrequency column value is zero, rows where AuditFrequency is NULL will also be ignored by the query.
It looks like it's designed to detect a null AuditFrequency as zero and thus hide those rows.
From what I can see, it checks for fields that aren't 0 or null.
I think it is more accurately described by this:
select AuditStatusId
from dbo.ABC_AuditStatus
where (AuditFrequency IS NOT NULL AND AuditFrequency != 0) OR 0 != 0
I'll admit the last part will never do anything and maybe i'm just being pedantic but to me this more accurately describes your query.
The idea is that it is desireable to express a single search condition using a single expression but it's merely style, a question of taste:
One expression:
WHERE age = COALESCE(#parameter_value, age);
Two expressions:
WHERE (
age = #parameter_value
OR
#parameter_value IS NULL
);
Here's another example:
One expression:
WHERE age BETWEEN 18 AND 65;
Two expressions
WHERE (
age >= 18
AND
age <= 65
);
Personally, I have a strong personal perference for single expressions and find them easier to read... if I am familiar with the pattern used ;) Whether they perform differently is another matter...