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);
Related
For example, I have a table with these values:
ID
Date
Col1
Col2
Col3
Col4
1
01/11/2021
A
A
B
2
01/11/2021
B
B
The A and B values are dynamic, they can be other characters as well.
Now I need somehow to get to the result that id 1 has 2 occurences of A and one of B. Id 2 has 0 occurences of A and 2 occurences of B.
I'm using dynamic SQL to do this:
for v_record in table_cursor
loop
for i in 1 .. 4
loop
v_query := 'select col'||i||' from table where id = '||v_record.id;
execute immediate v_query into v_char;
if v_char = "any letter I'm checking" then
amount := amount + 1;
end if;
end loop;
-- do somehting with the amount
end loop;
But there has to be a better much more efficient way to do this.
I don't have that much knowledge of plsql and I really don't know how to formulate this question in google. I've looked into pivot, but I don't think that will help me out in this case.
I'd appreciate it if someone could help me out.
Assuming the number of columns would be fixed at four, you could use a union aggregation approach here:
WITH cte AS (
SELECT ID, Col1 AS val FROM yourTable UNION ALL
SELECT ID, Col2 FROM yourTable UNION ALL
SELECT ID, Col3 FROM yourTable UNION ALL
SELECT ID, Col4 FROM yourTable
)
SELECT
t1.ID,
t2.val,
COUNT(c.ID) AS cnt
FROM (SELECT DISTINCT ID FROM yourTable) t1
CROSS JOIN (SELECT DISTINCT val FROM cte) t2
LEFT JOIN cte c
ON c.ID = t1.ID AND
c.val = t2.val
WHERE
t2.val IS NOT NULL
GROUP BY
t1.ID,
t2.val;
This produces:
Demo
I would like to query an Oracle DB table for the number of rows containing each distinct value in a CLOB column.
This returns all rows containing a value:
select * from mytable where dbms_lob.instr(mycol,'value') > 0;
Using DBMS_LOB, this returns the number of rows containing that value:
select count(*) from mytable where dbms_lob.instr(mycol,'value') > 0;
But is it possible to query for the number of times (rows in which) each distinct value appears?
Depending on what that column really contains, see whether TO_CHAR helps.
SQL> create table mytable (mycol clob);
Table created.
SQL> insert into mytable
2 select 'Query to count distinct values' from dual union all
3 select 'I have no idea which values are popular' from dual;
2 rows created.
SQL> select count(*), to_char(mycol) toc
2 from mytable
3 where dbms_lob.instr(mycol,'value') > 0
4 group by to_char(mycol);
COUNT(*) TOC
---------- ----------------------------------------
1 Query to count distinct values
1 I have no idea which values are popular
SQL>
If your CLOB values are more than 4000 bytes (and if not, why are they CLOBs?) then it's not perfect - collisions are possible, if unlikely - but you could hash the CLOB values.
If you want to count the number of distinct values:
select count(distinct dbms_crypto.hash(src=>mycol, typ=>2))
from mytable
where dbms_lob.instr(mycol,'value') > 0;
If you want to count how many times each distinct value appears:
select mycol, cnt
from (
select mycol,
count(*) over (partition by dbms_crypto.hash(src=>mycol, typ=>2)) as cnt,
row_number() over (partition by dbms_crypto.hash(src=>mycol, typ=>2) order by null) as rn
from mytable
where dbms_lob.instr(mycol,'value') > 0
)
where rn = 1;
Both are likely to be fairly expensive and slow with a lot of data.
(typ=>2 gives the numeric value for dbms_crypto.hash_md5, as you can't refer to the package constant in a SQL call, at least up to 12cR1...)
Rather more crudely, but possibly significantly quicker, you could base the count on the just the first 4000 characters - which may or may not be plausible for your actual data:
select count(distinct dbms_lob.substr(mycol, 4000, 1))
from mytable
where dbms_lob.instr(mycol,'value') > 0;
select dbms_lob.substr(mycol, 4000, 1), count(*)
from mytable
where dbms_lob.instr(mycol,'value') > 0
group by dbms_lob.substr(mycol, 4000, 1);
Standard Oracle functions do not support distinction of CLOB values. But, if you have access to DBMS_CRYPTO.HASH function, you can compare CLOB hashes instead, and thus, get the desired output:
select myCol, h.num from
myTable t join
(select min(rowid) rid, count(rowid) num
from myTable
where dbms_lob.instr(mycol,'value') > 0
group by DBMS_CRYPTO.HASH(myCol, 3)) h
on t.rowid = h.rid;
Also, note, that there's a very little possibility of hash collision. But if that's ok with you, you can use this approach.
I have two tables Table1 and Table2 both with the same columns TestResult and Testcounts. Table1 has testresult as varchar and Table2 has testresult as number.
I have a string .for eg "Oracle" as value for testresult of varchar type for Table1 which needs to be inserted to testresult of number type of Table2 as null.How can i do this? Any suggestions will be highly appreciated :)
EDIT
I have table1 with columns as TestResult varchar2(50) and Testcount number with values as "0.5","0.6","0.8","Oracle" for TestResult and 1,2,3,4 for Testcount.
Now i have another table Table2 as TestResult number and Testcount number with no values, in other words its empty.. I would like to insert all data from table1 to table2 with "Oracle" being inserted as "null"
The following will do what you've asked for:
INSERT INTO TABLE2 (TESTRESULT, TESTCOUNTS)
SELECT CASE
WHEN LENGTH(REGEXP_SUBSTR(TESTRESULT, '[0-9.]*')) = LENGTH(TESTRESULT) THEN TESTRESULT
ELSE NULL
END,
TESTCOUNTS
FROM TABLE1
SQLFiddle here
If you only have a single string value that you can't convert to a number, and you want to set that to null, you can just use a case expression to supply the null:
insert into table2 (testresult, testcounts)
select case when testresult = 'Oracle' then null else to_number(testresult) end,
testcounts
from table1;
Demo:
create table table1 (testresult varchar2(10), testcounts number);
insert into table1
select '0.5', 1 from dual
union all select '0.6', 2 from dual
union all select '0.8', 3 from dual
union all select 'Oracle', 4 from dual;
create table table2 (testresult number, testcounts number);
insert into table2 (testresult, testcounts)
select case when testresult = 'Oracle' then null else to_number(testresult) end,
testcounts
from table1;
select * from table2;
TESTRESULT TESTCOUNTS
---------- ----------
.5 1
.6 2
.8 3
4
db<>fiddle
If you are using Oracle 12c Release 2 (or above) you could also just try to convert the string to a number and use the default ... on conversion error clause to substitute null for that, or any other, non-numeric value:
insert into table2 (testresult, testcounts)
select to_number(testresult default null on conversion error), testcounts
from table1;
select * from table2;
TESTRESULT TESTCOUNTS
---------- ----------
.5 1
.6 2
.8 3
4
In earlier versions you could do the same thing with a user-defined function that wraps the real to_number() call and returns null on error. Or a regex/translate check similar to what #BobJarvis has shown.
Having multiple rows with null would make the data hard to interpret though, so hopefully you only have this one fixed value...
I have a gauge chart that displays a value label and a percentage. it is based on a query that returns VALUE and MAX_VALUE. In some cases the query returns 0 as MAX_VALUE and then the chart displays a message 'Invalid data'. I believe this is happening because of division by zero. How to prevent this message from getting displayed and return 0 as both VALUE and MAX_VALUE and 0%?
SELECT NUM_FAILED VALUE, TOTAL_NUM MAX_VALUE
FROM
(
SELECT (
SELECT COUNT(*) FROM (select t1.name, t1.run_id
from Table1 t1
LEFT JOIN Table2 t2 ON t1.ID=t2.ID
WHERE t1.START_DATE > SYSDATE - 1
GROUP BY t1.name, t1.run_id)
) AS TOTAL_NUM,
(
SELECT COUNT(*) FROM (select name, run_id
from Table1 t1
LEFT JOIN Tabe2 t2 ON t1.ID=t2.ID
where t1.run_id IN (SELECT run_id FROM Table1 where err_code > 0)
AND t1.START_DATE > SYSDATE - 1
GROUP BY t1.name, t1.run_id)
) as NUM_FAILED
FROM dual)
Thank you for posting a query.
If you want to avoid 0 as a result, how about DECODE?
SELECT decode(NUM_FAILED, 0, 1E99, NUM_FAILED) VALUE,
decode(TOTAL_NUM , 0, 1E99, TOTAL_NUM ) MAX_VALUE
FROM (the rest of your query goes here)
You didn't say what's going on afterwards (i.e. what exactly causes division by zero - is it NUM_FAILED, or TOTAL_NUM)? The idea is: instead of dividing by zero, divide by a very large value (such as 1E99) and you'll get a very small number, for example:
SQL> select 24/1E99 from dual;
24/1E99
----------
2,4000E-98
SQL>
which is, practically, zero. See if you can do something with such an approach.
I have table structure and data as below
https://ibb.co/mkGp67
I want a SQL Query to retrieve data only for those columns which have at least one not null value in it, in above case i want data comes out to be
https://ibb.co/mz9967
i.e. i don't need column Col2, Col5 and Col6, also which column having all null value is not fixed.
Please let me know the SQL query which retreive data that having only those column which having not null value with data as above.
As far, as I know, you will not be able to achieve this with an SQL query. One of the strong assumptions of SELECT statements is that the list of returned columns is static - defined in the query, not by the data. Even for PIVOT queries (available - as far, as I know - since Oracle 11), the list of columns is defined in the query, by providing a list of values to be converted to columns has to be explicitly given.
What you are looking for is some kind of code, dynamically generating the query. This can be PL/SQL, returning cursor references or any application code.
Edit:
What you could do with a query, is to have a clear information on which columns do contain nulls, which do not, etc. It could look something like this:
SELECT CASE
WHEN COUNT(*) = 0 THEN 'no rows'
WHEN COUNT(Col1) = 0 THEN 'all NULLs'
WHEN COUNT(Col1) = COUNT(*) THEN 'no NULLs'
ELSE 'some NULLs'
END Col1NullStatus,
CASE
WHEN COUNT(*) = 0 THEN 'no rows'
WHEN COUNT(Col2) = 0 THEN 'all NULLs'
WHEN COUNT(Col2) = COUNT(*) THEN 'no NULLs'
ELSE 'some NULLs'
END Col2NullStatus,
CASE
WHEN COUNT(*) = 0 THEN 'no rows'
WHEN COUNT(Col3) = 0 THEN 'all NULLs'
WHEN COUNT(Col3) = COUNT(*) THEN 'no NULLs'
ELSE 'some NULLs'
END Col3NullStatus,
CASE
WHEN COUNT(*) = 0 THEN 'no rows'
WHEN COUNT(Col4) = 0 THEN 'all NULLs'
WHEN COUNT(Col4) = COUNT(*) THEN 'no NULLs'
ELSE 'some NULLs'
END Col4NullStatus,
CASE
WHEN COUNT(*) = 0 THEN 'no rows'
WHEN COUNT(Col5) = 0 THEN 'all NULLs'
WHEN COUNT(Col5) = COUNT(*) THEN 'no NULLs'
ELSE 'some NULLs'
END Col5NullStatus,
CASE
WHEN COUNT(*) = 0 THEN 'no rows'
WHEN COUNT(Col6) = 0 THEN 'all NULLs'
WHEN COUNT(Col6) = COUNT(*) THEN 'no NULLs'
ELSE 'some NULLs'
END Col6NullStatus
FROM myTable
See SQL Fiddle for the above.
Edit 2:
And the output of this query would look something like this:
Col1NullStatus | Col2NullStatus | Col3NullStatus | Col4NullStatus | Col5NullStatus | Col6NullStatus
---------------+----------------+----------------+----------------+----------------+----------------
no NULLs | all NULLs | some NULLs | no NULLs | all NULLs | all NULLs
This is the format, you could be using, to post your input data and expected results.
So, since you give no no formal table structure, and you seem to be confusing numbers and chars(s), I will do my best to try and make a query that will at least produce the results you want.
create table foo as (
col1 varchar(10),
col2 varchar(10),
col3 varchar(10),
col4 varchar(10),
col5 varchar(10),
col6 varchar(10)
);
select *
CASE cust1 WHEN null then 'null' else cust1 as cust1 end,
CASE cust2 WHEN null then 'null' else cust1 as cust1 end,
CASE cust3 WHEN null then 'null' else cust1 as cust1 end,
CASE cust4 WHEN null then 'null' else cust1 as cust1 end,
CASE cust5 WHEN null then 'null' else cust1 as cust1 end,
CASE cust6 WHEN null then 'null' else cust1 as cust1 end
from foo ;
As per below query , I able to get not null columns at row-level col1,col3 and col4.
Query :
select 'col1' as "Name",col1 from temp
where exists (select 1
from temp
group by to_char(col1)
having (count(to_char(col1)))> 0)
union all
select 'col2' as "Name",to_char(col2) from temp
where exists (select 1
from temp
group by to_char(col2)
having (count(to_char(col2)))> 0)
union all
select 'col3' as "Name" , to_char(col3) from temp
where exists (select 1
from temp
group by to_char(col3)
having (count(to_char(col3)))> 0)
union all
select 'col4'as "Name" , to_char(col4) from temp
where exists (select 1
from temp
group by to_char(col4)
having (count(to_char(col4)))> 0)
union all
select 'col5' as "Name" , to_char(col5) from temp
where exists (select 1
from temp
group by to_char(col5)
having (count(to_char(col5)))> 0)
union all
select 'col6' as "Name" , to_char(col6) from temp
where exists (select 1
from temp
group by to_char(col6)
having (count(to_char(col6)))> 0)
output:
col1 A
col1 B
col1 C
col1 D
col3 10
col3 20
col3 -
col3 10
col4 12
col4 23
col4 34
col4 43
I tried to make this output of rows to columns but I couldn't make it in single query ... Hope this will be helpful ...
I would do this usually in three steps.
Firstly, make sure that the table statistics are up to date. Check if last_analyzed is later than the last change to the table.
SELECT last_analyzed FROM user_tables WHERE table_name = 'MYTABLE';
If in doubt, update the statistics with
BEGIN dbms_stats.gather_table_stats('MYSCHEMA','MYTABLE'); END;
/
Now, the view user_tab_columns has a column num_nulls. This is the number of rows where this column is NULL. If the value is the same than the number of rows in the table, all rows are NULL. This can be used to let Oracle generate the required SQL:
WITH
qtab AS (SELECT owner, table_name, num_rows
FROM all_tables
WHERE owner='SCOTT' -- change to your schema
AND table_name='EMPLOYEES' -- change to your table name
),
qcol AS (SELECT owner, table_name, column_name, column_id
FROM qtab t
JOIN all_tab_columns c USING (owner, table_name)
WHERE c.nullable = 'N' -- protected by NOT NULL constraint
OR c.num_nulls = 0 -- never NULL
OR c.num_nulls < t.num_rows -- at least 1 row is NOT NULL
)
)
SELECT 'SELECT '||LISTAGG(column_name,',') WITHIN GROUP (ORDER BY column_id)||
' FROM '||owner||'.'||table_name||';' AS my_query
FROM qcol
GROUP BY owner, table_name;
This will output a query like
SELECT col1, col3, col4, col5 FROM myschema.mytable;
This query can now be executed to show the column values.