I tried to:
select 1>2 from dual;
but got:
ORA-00923: FROM keyword not found where expected
Is there boolean type for column expression in Oracle SQL?
I able to do:
select case when 1>2 then 'T' else 'F' end from dual;
Originally I tried to compare date fields and the quickest way I found was getting difference and look to sign...
UPDATE I tried SIGN function, I don't know if it is vendor specific extension:
select SIGN(1-2) from dual;
select SIGN(DATE '2017-01-02' - DATE '2017-02-12') from dual;
but this trick doesn't work for strings...
No there is not, you can use 0 and 1 just as yes/no.
If you need to get the result 1 if something is true and 0 if it is false, you can use a case expression:
select case when (any_logical_condition_here) then 1 else 0 end as my_col
from ....
where ....
For example:
select case when 1 > 2 then 1 else 0 end as bool_result
from dual;
BOOL_RESULT
---------------------------------------
0
NOTE though - "Boolean" refers strictly to the TRUE/FALSE logic, it has no place for UNKNOWN. When you deal with null, as you must in SQL, you need three-valued logic. The case expression as written above returns 1 when the logical condition is true and 0 otherwise. Try it with 1 > null - the truth value is UNKNOWN, the case expression will return 0.
Related
In mysql you can do select name <> '' from persons where person_id = 1000 and it will return a 1 or zero, is there a way to do something similar in Firebird with DML? Based on what I've been able to determine I'm guessing not.
In Firebird 3 and later this is possible, as the introduction of the BOOLEAN data type now allows this type of expression in the select clause. Such a boolean expression will return true/false, although some tools might map that to 1/0 for you.
In Firebird 2.5 and earlier you will have to map this yourself, for example using CASE:
select case when name <> '' then 1 else 0 end from atable where person_id = 1000
or IIF:
select iif(name <> '', 1, 0) from atable where person_id = 1000
This also works in Firebird 3 and higher.
I have created a PL/SQL function where I have a case expression in a SQL query. This is working fine, but when I add another when condition it will not compile. Even if I use when ... and 2 > 1, this is also not compiling.
In the below code, the commented part is not working properly.
What I want is to add one more check in my when clause. Please advise.
create or replace function FUNCTION_NAME (date1 in varchar2,value1 in varchar2)
RETURN date
IS
date2 date;
BEGIN
SELECT D DATE2
INTO DATE2 FROM (SELECT CASE (SELECT TO_DATE(MAX(G.DATE3),'DD-MON-YYYY')
FROM TABLE1 G,
TABLE2 N
WHERE G.DATE3=N.DATE3)
WHEN LAST_DAY(TO_DATE(DATE1,'DD-MON-YYYY'))
/* AND MONTHS_BETWEEN (LAST_DAY(TO_DATE(SYSDATE)),
LAST_DAY(TO_DATE(TO_CHAR(DATE1),'DD-MON-YYYY'))) */
THEN LAST_DAY(TO_DATE(DATE1,'DD-MON-YYYY'))
ELSE
TO_DATE('31-DEC-99','DD-MON-YYYY')
END D
FROM DUAL);
RETURN DATE2;
END;
What you have is a case expression (not a case statement).
Case expressions are of two kinds: "simple" (case <expr> when val1 then ... when val2 then... etc.) and "searched" ( case when condition1 then ... when condition2 then ... etc.)
You wrote your case expression as a simple case expression. You can't, then, add conditions to the WHEN part. You must change the case expression to be "searched" all the way through.
case when (select ...) = last_day(...) AND <your commented condition> THEN .....
EDIT - copying part of a clarifying comment below my Answer.
Simple case expression:
case x when 1 then ....
Can also be written as searched case expression:
case when x = 1 then ....
These two are logically equivalent. However, if we want to add "AND 3 > 1" to the WHEN part, that works only in the searched form of the case expression.
There are two flavours of CASE.
Simple CASE:
select case dummy
when 'X' then 1
end as case_demo
from dual;
Searched CASE:
select case
when dummy = 'X' then 1
end as case_demo
from dual;
In your query you are mixing them like this, which won't work:
select case dummy
when 'X' and 1 = 1
then 1
end as case_demo
from dual;
If you switch to a "searched CASE", then you can add more when conditions:
select case
when dummy = 'X' and 1 = 1
then 1
end as case_demo
from dual;
This is my first post, and I attempted to do a thorough search for this issue, so please accept my apologies if it has been posted elsewhere many times, but I'm wondering if anyone has encountered the following issue when attempting to remove NULLs from their result set:
case Occurrence
when NULL then '0'
else occurrence
end as Occurrence,
case Aggregate
when NULL then '0'
else Aggregate
end as Aggregate,
This didn't do anything to my NULLs; however, this did the trick:
case
when occurrence is NULL then '0'
else occurrence
end as Occurrence,
case
when aggregate is NULL then '0'
else Aggregate
end as Aggregate
Does anyone have any idea why this behaves this way? I'm using SQLServer2012.
I'm also not very versed in programming and only have less than a year SQL experience.
Thanks!
You should be using the ISNULL() or COALESCE() system function for handling nulls
something like
SELECT ISNULL(Occurrence , 0) AS Occurrence
,ISNULL(Aggregate , 0) AS Aggregate
FROM Table
OR
SELECT COALESCE(Occurrence , 0) AS Occurrence
,COALESCE(Aggregate , 0) AS Aggregate
FROM Table
The reason it didn't work in the case statement with
case Occurrence
when NULL then '0'
else occurrence
end as Occurrence,
is because it is interpreting it as
CASE
WHEN Occurrence = NULL THEN 0
ELSE Occurrence
END
Null is checked in sql server using IS NULL or IS NOT NULL if you use any other operator with null like = , <> or <, < it yields NULL hence the unexpected results.
Only for SQL Server 2012 and Later
In sql server 2012 and later versions you also have the IIF function
SELECT IIF(Occurrence IS NULL, 0, Occurrence) AS Occurrence
,IFF(Aggregate IS NULL , 0, Aggregate) AS Aggregate
FROM Table
You use simple case:
The simple CASE expression operates by comparing the first expression to the expression in each WHEN clause for equivalency. If these expressions are equivalent, the expression in the THEN clause will be returned.
Allows only an equality check.
case Occurrence
when NULL then '0'
else occurrence
end as Occurrence,
Which is executed as :
case
when occurence = NULL then '0'
else occurrence
end as Occurrence
Then expression occurence = NULL return NULL and is treated like False
Second your case use searched CASE with full condition and works fine:
case
when occurrence IS NULL then '0'
else occurrence
end as Occurrence,
So your question is about difference column IS NULL vs column = NULL
try
select 1 where null =null
select 1 where null is null
your statement looks like null equals null
select case when null is null then 1 else 0 end
select case null when null then 1 else 0 end
In your case use ISNULL this will give you the results your after
SELECT ISNULL(null,1)
I have the following Searched Case field selection in a Oracle 10g SELECT query
(case
when LOADER_CELLS.CELL_MODE='RW' then 1
when LOADER_CELLS.CELL_MODE='R' then 2
end) as CELL_EDIT_MODE_ID
but if I write it as a Simple Case expression, as follows:
(case LOADER_CELLS.CELL_MODE
when 'RW' then 1
when 'R' then 2
end) as CELL_EDIT_MODE_ID
I get a ORA-12704: character set mismatch error on the when 'RW' line.
I gave a look to the Oracle documentation, and it seems my syntax is correct. http://docs.oracle.com/cd/B19306_01/server.102/b14200/expressions004.htm
Can someone help me on this?
" I supposed that it could be a encoding problem but I don't know how to "cast" the constant strings to a NVARCHAR"
you do it with "N" syntax.
case LOADER_CELLS.CELL_MODE
when n'RW' then 1
when n'R' then 2
end
eg
SQL> select case a when 'a' then 1 end from foo;
select case a when 'a' then 1 end from foo
*
ERROR at line 1:
ORA-12704: character set mismatch
SQL> select case a when n'a' then 1 end from foo;
CASEAWHENN'A'THEN1END
---------------------
I want to compare two numbers. Let's take i.e. 1 and 2.
I've tried to write the following query but it simply doesn't work as expected (Toad says: ORA-00923: FROM keyword not found where expected):
SELECT 1 > 2 from dual
The DECODE is something like a Switch case, so how can I get the result of an expression evalutation (i.e. a number comparison) putting it in the select list?
I have found a solution using a functions instead of an expression in the SELECT LIST: i.e.
select DECODE(SIGN(actual - target)
, -1, 'NO Bonus for you'
, 0,'Just made it'
, 1, 'Congrats, you are a winner')
from some_table
Is there a more elegant way?
Also how do I compare two dates?
There is no boolean types in sql (at least in oracle).
you can use case:
SELECT CASE when 1 > 2 THEN 1 ELSE 0 END FROM dual
But your solution (decode) is also good, read here
The SIGN() function is indeed probably the best way of classifying (in)equality that may be of interest to you if you want to test a > b, a = b and a < b, and it will accept date-date or numeric-numeric as an argument.
I'd use a Case statement by preference, rather than a decode.
Select
case sign(actual-target)
when -1 then ...
when 0 then ...
when 1 then ...
end
SELECT (CASE
WHEN (SIGN(actual - target) > 0 ) THEN
'NO Bonus for you'
ELSE
'Just made it' END)
FROM dual
you can compare two dates with sql
METHOD (1):
SELECT TO_DATE('01/01/2012') - TO_DATE('01/01/2012')
FROM DUAL--gives zero
METHOD (2):
SELECT CASE
when MONTHS_BETWEEN('01/01/2012','01/01/2010') > 0
THEN 'FIRST IS GREATER'
ELSE 'SECOND IS GREATER OR EQUAL' END
FROM dual
sorry i cant format the code the formatting toolbar disappeared !
do any one know why?