For the following:
col1 col2
1 null
3 null
5 100
6 200
10 null
11 201
How do I get the most recent col2==null rows using LINQ? This would be only col1= (1,3). These values are coming from a database.
The result set would be:
col1 col2
1 null
3 null
I'm not so familiar with Linq-To-Sql, so i'm not sure if it is supported, but try:
var query = db.TableName
.Where(r1 => r1.Col2 == null
&& r1.Col1 < db.TableName
.Where(r2 => r2.Col1 != null)
.Select(r2 => r2.Col1)
.OrderBy(col1 => col1)
.FirstOrDefault());
At least it should be the LINQ equivalent of this (working) sql-query: http://sqlfiddle.com/#!6/439be/6/0
Related
For every row of my data set, there exist data for the only one of the two options for calculation and the other columns are Null.
My goal is to find simplest way to select not null result of calculation for each row. Expected result:
ROW_NUM result
-------- -------
1 4.5
2 4.56
My code:
With DATASET AS (
-- column 1 is just for row number,
-- column 2 and 3 for caculation option1,
--- columns 4~6 for caculation option2
SELECT 1 ROW_NUM, NULL time1, NULL qty1, 2 time2_1, 2.5 time2_2, 1 qty2
FROM DUAL
UNION
SELECT 2 ROW_NUM, 4.56 time1, 1 qty1, NULL time2_1, NULL time2_2, NULL qty2
FROM DUAL
)
SELECT ROW_NUM, time1/qty1 OPTION1, (time2_1+time2_2)/qty2 OPTION2
FROM DATASET;
Result:
ROW_NUM OPTION1 OPTION2
-------- ------- ---------
1 4.5
2 4.56
You can decode and use different representation when null:
SELECT ROW_NUM, decode(time1/qty1,null,(time2_1+time2_2)/qty2,time1/qty1) result FROM DATASET;
Or nvl
SELECT ROW_NUM, nvl(time1/qty1,(time2_1+time2_2)/qty2,time1/qty1) result FROM DATASET;
NVL lets you replace null (returned as a blank) with a string in the results of a query.
use COALESCE function as following:
With DATASET AS (
--each row contain information for either option1 or 2
SELECT *
FROM
(
--column 1 is just for row number, column 2 and 3 for caculation option1, columns 4~6 for caculation option2
SELECT 1 ROW_NUM, NULL time1, NULL qty1 , 2 time2_1 , 2.5 time2_2, 1 qty2 FROM DUAL
UNION
SELECT 2 ROW_NUM, 4.56 time1 , 1 qty1 , NULL time2_1 , NULL time2_2 , NULL qty2 FROM DUAL
)
)SELECT ROW_NUM, coalesce(time1/qty1,(time2_1+time2_2)/qty2) as result FROM DATASET;
db<>fiddle demo
Cheers!!
This question already has answers here:
Create leading zero in Oracle
(2 answers)
Closed 6 years ago.
I am trying to update a column value. The column datatype is Number. As per the requirement, for the right records this column will be updated with 000. I have included this in the Else part of the condition but when the table is getting updated it's taking only 0 not 000. Please suggest. How can I make it 000?
MERGE INTO mem_src_extn t USING
(
SELECT mse.rowid row_id,
CASE WHEN mse.type_value IS NULL OR mse."TYPE" IS NULL OR mse.VALUE_1 IS NULL or mse.VALUE_2 IS NULL THEN 100
WHEN ( SELECT count(*) FROM cmc_mem_src cms WHERE cms.tn_id = mse.type_value ) = 0 THEN 222
WHEN count(mse.value_1) over ( partition by type_value ) > 1 THEN 333
ELSE 000 int_value_1 <-- here
FROM mem_src_extn mse
) u
ON ( t.rowid = u.row_id )
WHEN MATCHED THEN UPDATE SET t.int_value_1 = u.int_value_1
If your column int_value_1 is varchar2 use quote
MERGE INTO mem_src_extn t USING
(
SELECT mse.rowid row_id,
CASE WHEN mse.type_value IS NULL OR mse."TYPE" IS NULL OR mse.VALUE_1 IS NULL or mse.VALUE_2 IS NULL THEN '100'
WHEN ( SELECT count(*) FROM cmc_mem_src cms WHERE cms.tn_id = mse.type_value ) = 0 THEN '222'
WHEN count(mse.value_1) over ( partition by type_value ) > 1 THEN
'333'
ELSE '000' int_value_1
END
FROM mem_src_extn mse
) u
ON ( t.rowid = u.row_id )
WHEN MATCHED THEN UPDATE SET t.int_value_1 = u.int_value_1
but if you have a number as you say and want just to see 000 insead of 0
You may use to_char with format string
select to_char(int_value_1,'099') from mem_src_extn;
Given following table1
id category city value
100 A x 10
100 A y 20
100 B x 1000
101 A x 100
101 C x 2
102 B x 3
We want to transpose the values of category_city as columns, i.e.
id A_x A_y B_x B_y C_x
100 10 20 1000 NULL NULL
101 100 NULL NULL NULL 2
102 NULL NULL 3 NULL NULL
The "max(case when ...)" method mentioned in this thread doesn't works well. Say, even if we have only 100 distinct values of category and 10 distinct values of city, the combination of category_city will be 1000. We need to manually write 1000 lines of "case(when ...) as category_city". This is ugly.
SELECT t.userid
MAX(CASE WHEN t.fieldname = 'Username' THEN t.fieldvalue ELSE NULL END) AS Username,
MAX(CASE WHEN t.fieldname = 'Password' THEN t.fieldvalue ELSE NULL END) AS Password,
MAX(CASE WHEN t.fieldname = 'Email Address' THEN t.fieldvalue ELSE NULL END) AS Email
FROM TABLE t
GROUP BY t.userid
Any beautiful way to do this?
I have a table with two columns that might be null (as well as some other columns). I would like to count how many rows that have column a, b, both and neither columns set to null.
Is this possible with Oracle in one query? Or would I have to create one query for each? Can't use group by or some other stuff I might not know about for example?
COUNT(expr) will count the number of rows where expr is not null, thus you can count the number of nulls with expressions like these:
SELECT count(a) nb_a_not_null,
count(b) nb_b_not_null,
count(*) - count(a) nb_a_null,
count(*) - count(b) nb_b_null,
count(case when a is not null and b is not null then 1 end)nb_a_b_not_null
count(case when a is null and b is null then 1 end) nb_a_and_b_null
FROM my_table
Something like this:
SELECT sum(case
when a is null and b is null then 1
else 0
end) as both_null_count,
sum(case
when a is null and b is not null then 1
else 0
end) as only_a_is_null_count
FROM your_table
You can extend that for other combinations of null/not null
select sum(decode(a,null,0,1)) as "NotNullCount", sum(decode(a,null,1,0)) as "NullCount"
from myTable;
Repeat for as many fields as you like.
It can be accomplished in Oracle just in 1 row:
SELECT COUNT(NVL(potential_null_column, 0)) FROM table;
Function NVL checks if first argument is null and treats it as value from second argument.
This worked well for me for counting getting the total count for blank cells on a group of columns in a table in oracle: I added the trim to count empty spaces as null
SELECT (sum(case
when trim(a) is null Then 1
else 0
end)) +
(sum(case
when trim(b) is null
else 0
end)) +
(sum(case
when trim(c) is null
else 0
end)) as NullCount
FROM your_table
Hope this helps
Cheers.
SQL>CREATE TABLE SAMPLE_TAB (COL1 NUMBER NOT NULL, COL2 DATE DEFAULT SYSDATE, COL3 VARCHAR2(20));
SQL>INSERT INTO SAMPLE_TAB(COL1,COL2,COL3) VALUES(121,SYSDATE-2,'SAMPLE DATA');
SQL>INSERT INTO SAMPLE_TAB(COL1,COL2,COL3) VALUES(122,NULL,NULL); --ASSIGN NULL TO COL2
SQL>INSERT INTO SAMPLE_TAB(COL1,COL3) VALUES(123,'SAMPLE DATA RECORD 3');--COL2 DEFAULT VALUE ASSIGN AS SYSDDATE AS PER STRUCTURE.
SQL>COMMIT;
SQL> SELECT * FROM SAMPLE_TAB;
SQL> SELECT *
FROM USER_TAB_COLUMNS U
WHERE 1=1
AND TABLE_NAME='SAMPLE_TAB'
AND NUM_NULLS!=0;
SQL> ANALYZE TABLE SAMPLE_TAB COMPUTE STATISTICS;
SQL> SELECT *
FROM USER_TAB_COLUMNS U
WHERE 1=1
AND TABLE_NAME='SAMPLE_TAB'
AND NUM_NULLS!=0;
One way to do it would be:
select count(*) from table group by nvl2(a, 0, 1), nvl2(b, 0, 1) having nvl2(a,0,1) = nvl2(b,0,1);
I have a table that has 5 "optional" fields. I'd like to find out how many rows have all 5 null, how many have 1 field non-null, etc.
I've tried a couple of things, like:
select
count(*),
( (if field1 is null then 1 else 0) +
(if field2 is null then 1 else 0) +
etc.
but of course that doesn't work.
Ideally, I'm looking for output that's something like
Nulls Cnt
0 200
1 345
...
5 40
Is there an elegant solution?
The keyword is not if, it is case, and you must use end to end the case statement.
Here is a query that can suit you:
WITH subQuery AS
(
SELECT My_Table.*, (CASE WHEN My_Table.field1 IS NULL THEN 1 ELSE 0 END +
CASE WHEN My_Table.field2 IS NULL THEN 1 ELSE 0 END +
CASE WHEN My_Table.field3 IS NULL THEN 1 ELSE 0 END +
CASE WHEN My_Table.field4 IS NULL THEN 1 ELSE 0 END +
CASE WHEN My_Table.field5 IS NULL THEN 1 ELSE 0 END ) NumberOfNullFields
FROM My_Table
)
SELECT NumberOfNullFields, COUNT(*)
FROM subQuery
GROUP BY NumberOfNullFields;
While there is nothing wrong with the case WHEN counting, I just wanted to see if there was another way.
WITH SAMPLEDATA AS(--just generate some data with nulls for 5 cols
select level ,
(case when mod(level,2) = 0 then 1 else null end) colA,
(case when mod(level,3) = 0 then 1 else null end) colB,
(case when mod(level,5) = 0 then 1 else null end) colC,
(case when mod(level,7) = 0 then 1 else null end) colD,
(case when mod(level,11) = 0 then 1 else null end) colE
from dual
connect by level < 1000
), --utilize the count(Aggregate)'s avoidance of nulls to our summation advantage
nullCols as(
SELECT COUNT(COLA) aNotNull
,cOUNT(*)-COUNT(COLA) aNull
,count(colB) bNotNull
,cOUNT(*)-count(colB) bNull
,count(colc) cNotNull
,cOUNT(*)-count(colc) cNull
,count(cold) dNotNull
,cOUNT(*)-count(cold) dNull
,count(cole) eNotNull
,cOUNT(*)-count(cole) eNull
, cOUNT(*) TotalCountOfRows
from SAMPLEDATA )
SELECT (select count(*) from sampledata where cola is null and colb is null and colc is null and cold is null and cole is null) allIsNull
,nullCols.*
FROM nullCols;
ALLISNULL ANOTNULL ANULL BNOTNULL BNULL CNOTNULL CNULL DNOTNULL DNULL ENOTNULL ENULL TOTALCOUNTOFROWS
---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ----------------------
207 499 500 333 666 199 800 142 857 90 909 999
this utilizes the
If expression in count(expression)
evaluates to null, it is not counted:
as noted from here
This method, as is obvious above, does not 'eloquently' sum all null columns well. Just wanted to see if this was possible without the CASE logic.