I have a table and sample data as below.
create table MyTable
(
Col1 NUMBER,
Col2 VARCHAR2(30)
)
MyTable
Col1 Col2
1 | Val1
2 | Val2
3 | Val3
4 | Val4
Below is the query which is already written and deployed to the application by some one else.
SELECT Col2
FROM MyTable A WHERE Col1 IN (2,3,4)
AND NOT EXISTS
(SELECT 1
FROM MyTable B
WHERE B.Col1 <> A.Col1)
How does <> compare multiple values in this case?
Does it just compare with value 2? Or randomly compares with any value amoung 2,3 or 4?
The values are compare one by one.
If you have the sample data:
CREATE TABLE MyTable(col1, col2) AS
SELECT 1, 'Val1' FROM DUAL UNION ALL
SELECT 2, 'Val2' FROM DUAL UNION ALL
SELECT 3, 'Val3' FROM DUAL UNION ALL
SELECT 4, 'Val4' FROM DUAL;
Then:
SELECT *
FROM MyTable A
WHERE Col1 IN (2,3,4)
Will return 3 rows:
COL1
COL2
2
Val2
3
Val3
4
Val4
For your full query:
SELECT Col2
FROM MyTable A
WHERE Col1 IN (2,3,4)
AND NOT EXISTS(
SELECT 1
FROM MyTable B
WHERE B.Col1 <> A.Col1
)
Then for each of the rows it will check that a row does NOT EXISTS in the MyTable table where B.Col1 <> A.Col1. In your case, there are 3 rows that exist in the sub-query for each of the matched rows in the main query. You can see this with the query:
SELECT Col2,
(SELECT LISTAGG(col1, ',') WITHIN GROUP (ORDER BY col1)
FROM MyTable B
WHERE B.Col1 = A.Col1) AS equal,
(SELECT LISTAGG(col1, ',') WITHIN GROUP (ORDER BY col1)
FROM MyTable B
WHERE B.Col1 <> A.Col1) AS not_equal
FROM MyTable A
WHERE Col1 IN (2,3,4)
Which outputs:
COL2
EQUAL
NOT_EQUAL
Val2
2
1,3,4
Val3
3
1,2,4
Val4
4
1,2,3
Given that there is always (more than) one row that exists then the NOT EXISTS condition will exclude every row and your result set will be empty.
db<>fiddle here
Related
I have this table:
COL1 COL2 COL3
--------------------
A 1 VAL1
A 2 VAL2
A 4 VAL3
B 2 VAL4
B 4 VAL5
B 5 VAL6
And I would like to obtain this output:
COL1 COL2 COL3
--------------------
A 1 VAL1
A 2 VAL2
A 3 NULL
B 2 VAL4
B 3 NULL
B 4 VAL6
Logic:
with the smallest COL2 value for each partition of COL1, take the following 3 numbers and, if the combination COL1 and COL2 present in the first table, show COL3 and NULL otherwise.
Your question is a good example of what PARTITIONED OUTER JOIN was created for: DBFiddle
with top3 as (
select *
from (
select
col1, col2, col3
,min(col2)over(partition by col1) min_col2
,col2 - min(col2)over(partition by col1) + 1 as rn
from t
)
where col2 < min_col2 + 3
)
select
top3.col1
,r3.n as col2
,top3.col3
from
top3
partition by (col1)
right join
(select level n from dual connect by level<=3) r3
on r3.n=top3.rn;
As you can see, the first step is to get top3 and then just use partition by (col1) right join r3, where r3 is just generator of 3 rows.
Results:
COL1 COL2 COL3
----- ---------- ----
A 1 VAL1
A 2 VAL2
A 3
B 1 VAL4
B 2
B 3 VAL5
6 rows selected.
Note, this approach allows you to scan your table just once!
Let's see. Here is the table
select * from t order by col1, col2;
COL1 COL2 COL3
----- ---------- -----
A 1 VAL1
A 2 VAL2
A 4 VAL3
B 2 VAL4
B 4 VAL5
B 5 VAL6
6 rows selected
and now let's try to apply the described logic
with offsets as
(select level - 1 offset from dual connect by level <= 3),
smallest_col2 as
(select col1, min(col2) min_col2 from t group by col1)
select sc2.col1, sc2.min_col2 + o.offset col2, t.col3
from smallest_col2 sc2
cross join offsets o
left join t
on t.col1 = sc2.col1
and t.col2 = sc2.min_col2 + o.offset
order by 1, 2;
COL1 COL2 COL3
----- ---------- -----
A 1 VAL1
A 2 VAL2
A 3
B 2 VAL4
B 3
B 4 VAL5
6 rows selected
Use a recursive CTE to get the COL2s from the min of each COL1 up to the next 2 and then a left join to the table:
WITH cte(COL1, COL2, max_col2) AS (
SELECT COL1, MIN(COL2), MIN(COL2) + 2
FROM tablename
GROUP BY COL1
UNION ALL
SELECT COL1, COL2 + 1, max_col2
FROM cte
WHERE COL2 < max_col2
)
SELECT c.COL1, c.COL2, t.COL3
FROM cte c LEFT JOIN tablename t
ON t.COL1 = c.COL1 AND t.COL2 = c.COL2
ORDER BY c.COL1, c.COL2
See the demo.
The partitioned outer join, already demonstrated in Sayan's answer, is probably the best approach for that part of the assignment (data densification).
For the first part, in Oracle 12.1 and higher you can use the match_recognize clause:
select col1, col2, col3
from this_table
match_recognize(
partition by col1
order by col2
measures col2 - a.col2 + 1 as rn
all rows per match
pattern ( ^ a b* )
define b as col2 <= a.col2 + 2
)
partition by (col1)
right outer join
(select level as rn from dual connect by level <= 3) using (rn)
;
Another solution with the "recursive WITH clause"
With rws_numbered (COL1, COL2, COL3, rn) as (
select COL1, COL2, COL3
, row_number()over(order by col1, col3) rn
from Your_table
)
, cte ( COL1, COL2, COL3, rn ) as (
select COL1, COL2, COL3, rn
from rws_numbered
where rn = 1
union all
select
t.COL1
, case when t.col1 = c.col1 then c.col2 + 1 else t.col2 end COL2
, t.COL3
, t.rn
from rws_numbered t
join cte c
on c.rn + 1 = t.rn
)
select COL1, COL2, case when exists (select null from Your_table t where t.COL1 = cte.COL1 and t.COL2 = cte.COL2) then COL3 else null end COL3
from cte
order by 1, 2
;
db<>fiddle
I have a table A like this :
col1col2col3
1 0null
nullnullnull
3nullnull
null 5 1
I want an output like this in Oracle 10G :
column_namenull_count
col1 2
col2 2
col3 3
I have achieved this using UNION ALL like this:
select "col1" column_name,sum(case when col1 is null then 1 else 0 end) as null_count from A group by "col1"
union all
select "col2" column_name,sum(case when col2 is null then 1 else 0 end) as null_count from A group by "col2"
union all
select "col3" column_name,sum(case when col3 is null then 1 else 0 end) as null_count from A group by "col3";
It is working fine , but it is taking lots of time , as there are nearly 100 UNION ALLs . I want to achieve the same output without using UNION ALL.
Is there any way to achieve this without using UNION ALL ?
You can use UNPIVOT for that (I am not sure if the ancient Oracle 10 already supported that - I haven't used that for over a decade)
select colname, count(*) - count(val) as num_nulls
from t1
UNPIVOT include nulls
(val for colname in (col1 as 'C1',
col2 as 'C2',
col3 as 'C3'))
group by colname
order by colname;
Not sure if that is faster though.
Online example: https://dbfiddle.uk/?rdbms=oracle_11.2&fiddle=4e807b8b2d8080abac36574f776dbf04
Oracle 10g doesn't support the UNPIVOT and PIVOT operators, so to do what you're after in 10g, you'd need to use a dummy table (containing the same number of rows as columns being unpivoted - in your case, that's 3), like so:
WITH your_table AS (SELECT 1 col1, 0 col2, NULL col3 FROM dual UNION ALL
SELECT NULL col1, NULL col2, NULL col3 FROM dual UNION ALL
SELECT 3 col1, NULL col2, NULL col3 FROM dual UNION ALL
SELECT NULL col1, 5 col2, 1 col3 FROM dual)
SELECT CASE WHEN dummy.id = 1 THEN 'col1'
WHEN dummy.id = 2 THEN 'col2'
WHEN dummy.id = 3 THEN 'col3'
END column_name,
COUNT(CASE WHEN dummy.id = 1 THEN CASE WHEN col1 IS NULL THEN 1 END
WHEN dummy.id = 2 THEN CASE WHEN col2 IS NULL THEN 1 END
WHEN dummy.id = 3 THEN CASE WHEN col3 IS NULL THEN 1 END
END) null_count
FROM your_table
CROSS JOIN (SELECT LEVEL ID
FROM dual
CONNECT BY LEVEL <= 3) dummy
GROUP BY dummy.id;
COLUMN_NAME NULL_COUNT
----------- ----------
col1 2
col2 2
col3 3
If you think that will take an age to write for a large number of columns, you can always write a query that will generate the bulk of the case statements yourself, e.g.:
SELECT 'when dummy.id = '||row_number() OVER (PARTITION BY owner, table_name ORDER BY column_id)||' then '''||LOWER(column_name)||'''' first_part,
'when dummy.id = '||row_number() OVER (PARTITION BY owner, table_name ORDER BY column_id)||' then case when '||column_name||' is null then 1 end' second_part
FROM all_tab_columns a
WHERE owner = ...
AND table_name = ...
-- and column_name in (...)
ORDER BY column_id;
(I included the row_number() analytic function rather than using column_id because if you're excluding some columns, the column_id column will no longer be consecutive numbers starting with 1.)
I have a table of two columns
Col1 Col2
A 1
A 2
A 3
B 1
B 2
B 3
Output I need is like this
Col1 Col2
A 1
A 1,2
A 1,2,3
B 1
B 1,2
B 1,2,3
Thank you in advance.
Here is a solution which would work for MySQL. It uses a correlated subquery in the select clause to group concatenate together Col2 values. The logic is that we only aggregate values which are less than or equal to the current row, for a given group of records sharing the same Col1 value.
SELECT
Col1,
(SELECT GROUP_CONCAT(t2.Col2 ORDER BY t2.Col2) FROM yourTable t2
WHERE t2.Col2 <= t1.Col2 AND t1.Col1 = t2.Col1) Col2
FROM yourTable t1
ORDER BY
t1.Col1,
t1.Col2;
Demo
Here is the same query in Oracle:
SELECT
Col1,
(SELECT LISTAGG(t2.Col2, ',') WITHIN GROUP (ORDER BY t2.Col2) FROM yourTable t2
WHERE t2.Col2 <= t1.Col2 AND t1.Col1 = t2.Col1) Col2
FROM yourTable t1
ORDER BY
t1.Col1,
t1.Col2;
Demo
Note that the only real change is substituting LISTAGG for GROUP_CONCAT.
with s (Col1, Col2) as (
select 'A', 1 from dual union all
select 'A', 2 from dual union all
select 'A', 3 from dual union all
select 'B', 1 from dual union all
select 'B', 2 from dual union all
select 'B', 3 from dual)
select col1, ltrim(sys_connect_by_path(col2, ','), ',') path
from s
start with col2 = 1
connect by prior col2 = col2 - 1 and prior col1 = col1;
C PATH
- ----------
A 1
A 1,2
A 1,2,3
B 1
B 1,2
B 1,2,3
6 rows selected.
WE have below data in oracle database -
col1 col2
Z1 A
Z1 B
Z2 A
Z2 C
Z3 A
Z4 D
I want count on column two in such a way that -
Ouput -
col2 count
A 3 (Z1,Z2,Z3)
B 0 (Dont count if A is already present for record)
C 0
D 1 (Z4)
Best Regards
You can use window function rank() to achieve this.
select col2, count(case when rn = 1 then 1 end) cnt from (
select t.*,
rank() over (partition by col1 order by case when col2 = 'A' then 1 else 2 end) rn
from table t
) group by col2;
The most general solution to your propositions where each key COL1 is counted only in the first occurrence of the key COL2 (in alphabetical order)
WITH tab AS
(
SELECT 'Z1' col1, 'A' col2 FROM dual UNION ALL
SELECT 'Z1' col1, 'B' col2 FROM dual UNION ALL
SELECT 'Z2' col1, 'A' col2 FROM dual UNION ALL
SELECT 'Z2' col1, 'C' col2 FROM dual UNION ALL
SELECT 'Z3' col1, 'A' col2 FROM dual UNION ALL
SELECT 'Z4' col1, 'D' col2 FROM dual
), tab2 as (
select COL1, COL2,
row_number() over (partition by COL1 order by COL2) as rn
from tab)
select COL1, COL2,
case when rn = 1 then 1 else 0 end is_valid
from tab2
order by 1,2
;
COL1 COL2 IS_VALID
---- ---- ----------
Z1 A 1
Z1 B 0
Z2 A 1
Z2 C 0
Z3 A 1
Z4 D 1
The rest is simple group by with a SUM on IS_VALID
select COL2, sum(is_valid) cnt from tab3 -- TAB3 is the above row source
group by COL2
order by 1
COL2 CNT
---- ----------
A 3
B 0
C 0
D 1
Thanks Guys. But I could do this way -
select count(case
when (LISTAGG(col2,'-') WITHIN GROUP (ORDER BY col2)) like '%A%' then 1
else null
end) A,
count(case
when (LISTAGG(col2,'-') WITHIN GROUP (ORDER BY col2)) = 'B' then 1
else null
end) B,
count(case
when (LISTAGG(col2,'-') WITHIN GROUP (ORDER BY col2)) = 'C' then 1
else null
end) C,
count(case
when (LISTAGG(col2,'-') WITHIN GROUP (ORDER BY col2)) = 'D' then 1
else null
end) D
from T
GROUP BY col1
Thanks for your replies
Assume your table name is table_name, One way to do it is using this:
WITH table_a AS
(
SELECT DISTINCT col1
FROM table_name
WHERE col2 = 'A'
)
SELECT col2,
SUM(CASE WHEN col1 IN (SELECT col1 FROM table_a)
THEN DECODE(col2, 'A', 1, 0)
ELSE 1 END
) count
FROM table_name
GROUP BY col2
ORDER BY col2;
Tested ok:
WITH table_name AS
(
SELECT 'Z1' col1, 'A' col2 FROM dual UNION ALL
SELECT 'Z1' col1, 'B' col2 FROM dual UNION ALL
SELECT 'Z2' col1, 'A' col2 FROM dual UNION ALL
SELECT 'Z2' col1, 'C' col2 FROM dual UNION ALL
SELECT 'Z3' col1, 'A' col2 FROM dual UNION ALL
--SELECT 'Z4' col1, 'B' col2 FROM dual UNION ALL
SELECT 'Z4' col1, 'D' col2 FROM dual
)
, table_a AS
(
SELECT DISTINCT col1
FROM table_name
WHERE col2 = 'A'
)
SELECT col2,
SUM(CASE WHEN col1 IN (SELECT col1 FROM table_a)
THEN DECODE(col2, 'A', 1, 0)
ELSE 1 END
) count
FROM table_name
GROUP BY col2
ORDER BY col2;
You want to count each record where either col2 is 'A' or no 'A' record exists for col1.
select
col2,
count(
case
when col2 = 'A' or col1 not in (select col1 from table_name where col2 = 'A') then 1
end) as cnt
from table_name
group by col2;
select col2, count(case when col2 = col3 then 'x' end) as ct
from ( select col2, min(col2) over (partition by col1) as col3
from your_table
)
group by col2
order by col2 -- if needed
;
Explanation:
There is an inner query (a.k.a. "subquery") which returns one row for each row in the original table. It returns col2 as is, and an additional (new) column, labeled col3. col3 is calculated as the "first" or min() value of col2 (in alphabetical order) for all the rows in the original table that have the same value in col1 as the current row does. This is a typical example of an analytic function; partition by col1 is similar to group by col1 but it returns all the rows in the group (all the original rows from the original table) instead of one row per group, as would an aggregate function.
To see what the inner query does by itself, select it and run it in your favorite front-end. You may add col1 to the select in the inner query - that will make what's going on in this query even clearer. You'll get the initial table, with one more column, col3, that shows the "min" col2 for each value of col1. I didn't include col1 in the subquery because I don't need it, but add it back to see what the subquery really does.
Then in the outer query I take the results from the inner query and I group by col2. For each col2 I count just how many times it is equal to the "min" value of col2 for the corresponding col1 value. That's what the case expression does in the count() function; when col2 is not equal to col3, then case returns null (by default) so the expression - and therefore the row - is not counted.
I should add that the query written this way assumes there are no duplicate (col1, col2) rows in the original table. If there are, then the inner subquery should select from a sub-subquery; line 3 of my code should be
from (select distinct col1, col2 from your_table)
Use the below script:
SELECT A.COL2, NVL(B.CNT, 0) AS CNT
FROM (SELECT DISTINCT COL2 FROM TET) A
LEFT JOIN (SELECT COL2, COUNT(COL2) AS CNT
FROM (SELECT SUBSTR(F, 1, INSTR(F, ',') - 1) AS COL2,
ROW_NUMBER() OVER(PARTITION BY SUBSTR(F, 1, INSTR(F, ',') - 1) ORDER BY SUBSTR(F, 1, INSTR(F, ',') - 1)) AS U
FROM (SELECT COL1,
LISTAGG(COL2, ',') WITHIN GROUP(ORDER BY COL2) || ',' AS F
FROM TET
GROUP BY COL1)) A
GROUP BY COL2) B
ON A.COL2 = B.COL2
ORDER BY A.COL2;
My table:
Col1 Col2
1 xyz
1 abc
2 abc
3 yyy
4 zzz
4 zzz
I have a table with two columns. I want to query for records where col1 has more than one DISTINCT col2 values. In the example table given above, the query should return records for col1 with value "1".
Expected query result:
Col1 Col2
1 xyz
1 abc
SELECT *
FROM tableName
WHERE Col1 IN
(
SELECT Col1
FROM tableName
GROUP BY Col1
HAVING COUNT(DISTINCT col2) > 1
)
SQLFiddle Demo
select t.col1, t.col2
from (
select col1
from tbl
group by col1
having MIN(col2) <> MAX(col2)
) x
join tbl t on t.col1 = c.col1