In SQL Server, I am trying to update null fields in a table with existing vales in the table.
Example:
Table has 4 columns:A,B,C,D
A B C D
1 2 3 4
5 Null Null 4
How can I populate the Null values with the values in B,C where D=4
Update Table
Set B=B
Where B is null
and D=4
One option is to use a self join:
update t
set t.b = t2.b
from yourtable t
join yourtable t2 on t.d = t2.d
and t2.b is not null
where t.b is null
What if multiple records exist for b grouped by d where b is not null? That could mess this up. Instead you'd have to decide which value to use. Here's an example choosing the min:
update t
set t.b = t2.b
from yourtable t
join (select d, min(b) b
from yourtable
where b is not null
group by d) t2 on t.d = t2.d
where t.b is null
Or with a correlated subquery:
update yourtable t
set b = (select min(b) from yourtable t2 where t.id = t2.id)
where t.b is null
A lot of options here...
Related
I have this tables:
I need to update sum_ok and avg_ok considering values from table 1 like this:
I have this code SQL, but don't work fine:
update
t2
set sum_ok = sum(case when t2.[status]='OK' then 1 else 0 end )
,avg_ok = avg(case when t2[status]='OK' then status end )
from t1
inner join t2
on t1.A = t2.A --and t1.C = t2.C
where C is not null
group by A, C
Thanks!!
One option is to compute your "sum_ok" and "avg_ok" values separately, then apply the UPDATE statement while joining your "t2" table and your computed values:
WITH cte AS (
SELECT A,
C,
SUM(CASE WHEN [status] = 'ok' THEN 1 END) AS sum_ok,
AVG(CAST ([value] AS FLOAT)) AS avg_ok
FROM t1
GROUP BY A, C
)
UPDATE t2
SET t2.sum_ok = cte.sum_ok,
t2.avg_ok = cte.avg_ok
FROM t2
INNER JOIN cte
ON t2.A = cte.A AND t2.C = cte.C;
Check the demo here.
Note: in your query you're trying to access the "t2.status" field, whereas "t2" table doesn't have it.
I have written the query:
Select distinct a,b from t1 minus Select distinct a,b from t2.
Here t1 and t2 are two tables. I want distinct values of a and b that occur in t1 but not in t2. So I'm using minus operator. I want values of both a and b but I know that in some cases the value of b in t1 and t2 maybe different. This would result in values of a and b that are present in both t1 and t2 as minus would not happen if values of b do not match in both the tables. How can I do this successfully?
How can I get values of a and b that are present in table t1 but not in table t2 even though in some cases values of b might not match in both the tables?
table1: table2:
column1 column2 column1 column2
1 a 1 c
2 b 3 d
In this case I would want values (2,b) only. I would not want (1,a) as 1 is also present in table2.
Start with not exists:
select distinct. . .
from t1
where not exists (select 1 from t2 where t2.a = t1.a and t2.b = t1.b);
From you describe, you might want the comparison only on a:
select distinct a, b
from t1
where not exists (select 1 from t2 where t2.a = t1.a);
Another option is to use sub query in the WHERE condition as below-
SELECT A.*
FROM table1 A
WHERE A.column1 NOT IN
(SELECT DISTINCT column1 FROM table2)
You can also use LEFT JOIN as below which will provide you the same output as below-
SELECT A.*
FROM table1 A
LEFT JOIN table2 B ON A.column1 = B.column1
WHERE B.column1 IS NULL
For the data not include in t2, you can either go for the NOT EXISTS or LEFT OUTER JOIN.
Here is the solution.
Using NOT EXISTS
SELECT DISTINCT A,B FROM T1 WHERE NOT EXISTS (SELECT 1 FROM T2 WHERE T2.A = T1.A AND T2.B = T1.B);
Using Left Join
SELECT DISTINCT a,b,c FROM T1 LEFT JOIN T2 ON T1.a = T2.a and T1.b = T2.b WHERE T2.a IS NULL AND T2.b IS NULL
Hope it helps.
I am having an issue in extracting data using data of two tables in SQL.
select A, B, C, D
from Table_one T1
where A in (select T2.A from Table_two T2
where T2.E <> 'ZZZ');
This returns A, B, C, D where E in T2 is not ZZZ.
However, when I add another where clause like below,
it returns data where T2 is ZZZ also.
select A, B, C, D
from Table_one T1
where A in (select T2.A from Table_two T2
where T2.E <> 'ZZZ')
and D <> 0 ;
This ignores "T2.E <> 'ZZZ'" part, but "D<>0" is not ignored.
Why is this happening?
Because you have duplicates in Table_two. For some of those duplicates, one has the value of ZZZ and the other does not.
You are using the wrong logic if you want to exclude rows that have a ZZZ in table_two. I would recommend NOT EXISTS:
select A, B, C, D
from Table_one T1
where not exists (select 1
from Table_two T2
where T1.A = T2.A and
T2.E = 'ZZZ'
) and
D <> 0 ;
How do I get not-null results from a sub query in SELECT statement?
SELECT a, b, c,
(SELECT d
FROM table2
WHERE ...) as d
FROM table 1
WHERE ...
I want to get results only when all values (a, b, c , d) not Null.
It won't be kind of weird/non-efficient to use the same sub-query in main WHERE clause as well but with EXISTS?
The easiest way to do this is to put your original query in a subquery, then you can check whether the whole row that the subquery returns is NULL:
SELECT *
FROM (
SELECT a, b, c,
(SELECT d
FROM table2
WHERE ...)
FROM table 1
WHERE ...
) AS sub
WHERE sub IS NOT NULL
sub being the row of (a,b,c,d) returned by the subquery.
You can use a subquery:
select a, b, c, d
from (SELECT a, b, c,
(SELECT d
FROM table2
WHERE ...) as d
FROM table 1
WHERE ... and
a is not null and b is not null and c is not null
) x
where d is not null;
In all likelihood, though, you can use JOIN:
SELECT a, b, c, x.d
FROM table 1 JOIN
(SELECT d
FROM table2
WHERE ...
) x
WHERE ... and
a is not null and b is not null and c is not null and d is not null;
SELECT
t1.a,
t1.b,
t1.c,
t2.d
FROM table1 t1
left join table2 as t2 on t2.ID = t1.ID
WHERE t1.a is not null and t1.b is not null and t1.c is not null and t2.d is not null
I want to get the top 1 row for each unique value of b with the minimum value of c for that particular value of b. Even though there can be more than 1 row with the same min value (just chose the first one)
myTable
a integer (unique)
b integer
c integer
I've tried this query
SELECT t1.*
FROM myTable t1,
(SELECT b,
MIN(c) as c
FROM myTable
GROUP BY b) t2
WHERE t1.b = t2.b
AND t1.c = t2.c
However, in this table it's possible for there to be more than 1 instance of the minimum value of c for a given value of b. The above query generates duplicates under these conditions.
I've got a feeling that I need to use rownum somewhere, but I'm not quite sure where.
You can use ROW_NUMBER:
SELECT *
FROM (
SELECT *, ROW_NUMBER() OVER (PARTITION BY b ORDER BY c) AS rn
FROM myTable
) AS T1
WHERE rn = 1
To tie-break between the equal c's, you will need to subquery one level further to get the min-a for each group of equal c's per b. (A mouthful!)
select t0.*
FROM myTable t0
inner join (
select t1.b, t1.c, MIN(a) as a
from myTable t1
inner join (
select b, min(c) as c
from myTable
group by b
) t2 on t1.b = t2.b and t1.c = t2.c
group by t1.b, t1.c
) t3 on t3.a = t0.a and t3.b = t0.b and t3.c = t0.c