I have a table with duplicate records in all but one field (col4 for ex). I just need to delete the duplicate entries where the t1.col4 field is blank.
ID Col1 Col2 Col3 Col4
1 Joe 1 2 Yes
2 Sue 1 2
3 Joe 2 3
4 Joe 1 2
Goal: Delete only ID 4
I have tried both the inner join (I don't think msaccess allows this) and WHERE EXISTS/IN techniques with errors.
Exists technique deletes all records where t1.col4 is null (not just ones matched in subquery):
DELETE t1.*
FROM t1
WHERE Exists (
SELECT t1.col1, t1.col2, t1.col3
FROM t1
Group by t1.col1, t1.col2, t1.col3
HAVING Count(*) > 1
)
AND t1.col4 Is Null;
I've tried multiple iterations of the Inner Join technique but everything I've read here suggests it is not supported in Access. Happy to post what I've tried if it helps. I've also tried writing the subquery to a temptable and then trying to delete records matched by the inner join.
You need a correlated subquery:
DELETE t1
FROM t1
WHERE EXISTS (SELECT t1.col1, t1.col2, t1.col3
FROM t1 as tt1
WHERE t1.col1 = tt1.col1 AND t1.col2 = tt1.col2 AND t1.col3 = tt1.col3 AND t1.id <> tt1.id
) AND
t1.col4 Is Null;
Related
table 1
col1 col 2
A aaa
B bbb
C ccc
table 2
col1 col 2 col3
A aaa xx
B bbb yy
C ccc zz
D ddd hh
E eee mm
How to write a query where i get all of table1 data and only col3 to existing records of Table 1. table1 has only 50 records and Table2 has 100k. But i need only all 50 records of Table 1 and only col3 added to the record by joining
table1. col1 = table2.col1
Based on the description, I would suggest this query:
SELECT
t1.col1,
t2.col2,
t2.col3
FROM
table1 AS t1
INNER JOIN
table2 AS t2 ON (t2.col1 = t1.col1 AND t2.col2 = t1.col2)
The SELECT clause determines what columns will appear in the result set. Your description gives us some assistance here.
For a join, choosing the correct join type is important to what query you are making. Your description is helpful for this:
How to write a query where I get all of table1 data and only col3 to existing records of Table 1.
“get all of table1” implies that the result set should include all columns from that table.
SELECT table1.col1, table1.col2 […]
“get all of table1” implies that table1 is the primary source in the FROM clause.
[…] FROM table1 […]
“only col3 [from table2]” implies that the result set should also include that column.
SELECT […] table2.col3
“only […] to existing records of table1” implies that the join type is INNER JOIN.
FROM table1
INNER JOIN table2 […]
“only col3 to existing records of table1” implies that is the join condition.
FROM table1
INNER JOIN table2 ON table2.[…] = table1.[…]
But you don't specify exactly what condition tells us what records are equivalent between the tables. Shall we assume that the condition is for all columns named the same to have the same value?
FROM table1
INNER JOIN table2 ON (table2.col1 = table1.col1 AND table2.col2 = table1.col2)
We will be using the tables several times, so it's good practice to set concise AS aliases in the FROM clause.
You want INNER JOIN :
SELECT t1.col1, t1.col2, t2.col3
FROM table1 t1 INNER JOIN
table2 t2
ON t2.col1 = t1.col1;
Try left join:
SELECT t1.col1, t1.col2, t2.col3
FROM table1 t1 LEFT JOIN
table2 t2
ON t1.col1 = t2.col1 AND t1.col2 = t2.col2;
I have a source table A with a number of columns. I want to do a transformation of the source table to a target table. I would like to have a mapping table with same columns as the source table A and with rows that make up the translations.
Here is an example of the table A:
COL1 COL2 COL3
aktie ja 2
aktie nej 3
obli ja 2
and here is the mapping table
COL1 COL2 COL3 TRANSFORM
aktie ja NULL 3
aktie NULL NULL 4
Now, the idea is to join the source table with the mapping and get the transformed value returned. The use of NULL should serve as a wildcard. So my desired result should be that the first row in table A would match the first row in the mapping table and return the value 3
For the second row - and here is my challenge - I want it to match the second row in the mapping table because it is NOT matched by rows that have a value already (which would result in the transformed value 3) and as the second mapping row has NULL in column two, it should be treated as a wildcard (although taking into account other rows in the mapping table as well).
My first attempt would be something like
select A.*, m.res
from tab1 A
inner join mapping m on t.col1 = isnull(m.col1, t.col1)
and t.col2 = isnull(m.col2, t.col2)
and ...
but the problem is that the isnull(..,..) will match everything and not only return matches except the listed possible values that would result in a different transformation.
I am looking for a generic solution that would Work for any table with any number of columns, not only this particular table-layout mentioned here.
I have been thinking a lot about this and cannot really seem to come up with the solution, so please help :)
Here is one way to do this using a CTE (will work on SQL Server and Oracle)
WITH Map3 as
( -- TRANSFORM WILL BE NULL IF A MATCH WAS NOT MADE
SELECT T1.COL1, T1.COL2, T1.COL3, M.TRANSFORM
FROM Table1 T1
LEFT JOIN Mapping M ON T1.COL1 = M.COL1
AND T1.COL2 = M.COL2
AND T1.COL3 = COALESCE(M.COL3, T1.COL3)
), Map2 as
(
SELECT T1.COL1, T1.COL2, T1.COL3, COALESCE(T1.TRANSFORM,M.TRANSFORM)
FROM Map3 T1
LEFT JOIN Mapping M ON T1.COL1 = M.COL1
AND T1.COL2 = COALESCE(M.COL2, T1.COL2)
AND T1.TRANSFORM IS NULL
)
SELECT *
FROM Map2
I believe it is clear how this works and how to "extend" this to more columns.
If you can't use a CTE this is functionally the same and can be nested as far as you like:
SELECT T1.COL1, T1.COL2, T1.COL3, COALESCE(T1.TRANSFORM,M.TRANSFORM)
FROM (
-- TRANSFORM WILL BE NULL IF A MATCH WAS NOT MADE
SELECT T1.COL1, T1.COL2, T1.COL3, M.TRANSFORM
FROM Table1 T1
LEFT JOIN Mapping M ON T1.COL1 = M.COL1
AND T1.COL2 = M.COL2
AND T1.COL3 = COALESCE(M.COL3, T1.COL3)
) T1
LEFT JOIN Mapping M ON T1.COL1 = M.COL1
AND T1.COL2 = COALESCE(M.COL2, T1.COL2)
AND T1.TRANSFORM IS NULL
I am working on SQL 2008. I have two identical tables with same column names.
On Table2, i am missing some records. Some records got deleted in the Table2.
I have to compare Table1 and Table2 and retrieve only missing records from table1.
Use a LEFT JOIN and check for IS NULL like below. where t2.col2 is null will be TRUE only when there are records in table1 which are not present in table2. Which is what you are looking for. [This is a sample code and have no resemblance with your original query]
select t1.col1,t1.col2,t1.col3
from table1 t1
left join table2 t2 on t1.some_column = t2.some_column
where t2.col2 is null
You should use SQL Except. There is no Join involved.
Select * from dbo.TableA
Except
Select * from dbo.TableB
In set theory, the difference of sets A, B (A-B) is the set of elements that belong to A and do not belong to B.
With an " not exists", you have a solution :
select * from Table1 t1 where not exists (select 1 from Table2 t2
where t1.col1 = t2.col1
and t1.col2 = t2.col2
and t1.col3 = t2.col3
and ... // check here all columns ...
)
There is however a little problem in this solution in the case of null values, which can only be tested via a "IS NOT NULL" or "IS NULL", hence the complementary solution:
select * from Table1 t1 where not exists (select 1 from Table2 t2
where (t1.col1 = t2.col1 or (t1.col1 IS NULL and t2.col1 IS NULL))
and (t1.col2 = t2.col2 or (t1.col2 IS NULL and t2.col2 IS NULL))
and (t1.col3 = t2.col3 or (t1.col3 IS NULL and t2.col3 IS NULL))
and ... // check here all columns ...
)
I have 2 tables table A and table B. In table B we have to check if all the column entered is exactly as in table A, means if a row exists in table B then the same row will be there in table A too. also table A may have rows which are not in table B. if there is a row which is not in table A and is there in table B, an alert should be displayed showing which element is extra in table B.
Can we do this using join? if so what will be the sql code?
this is the best picture about joins i've ever seen :)
You probably want to have a look at the following article
SQL SERVER – Introduction to JOINs – Basic of JOINs
This should give you a very clear understanding of JOINs in Sql.
From there you should be able to find the solution.
As an example, you would have to look at something like
TABLE1
Col1
Col2
Col3
Col4
TABLE2
Col1
Col2
Col3
Col4
--all rows that match
SELECT *
FROM TABLE1 t1 INNER JOIN
TABLE2 t2 ON t1.Col1 = t2.Col1
AND t1.Col2 = t2.Col2
...
AND t1.Col3 = t2.Col3
--rows only in TABLE1
SELECT *
FROM TABLE1 t1 LEFT JOIN
TABLE2 t2 ON t1.Col1 = t2.Col1
AND t1.Col2 = t2.Col2
...
AND t1.Col3 = t2.Col3
WHERE t2.Col1 IS NULL
--rows only in TABLE2
SELECT *
FROM TABLE1 t2 LEFT JOIN
TABLE2 t1 ON t1.Col1 = t2.Col1
AND t1.Col2 = t2.Col2
...
AND t1.Col3 = t2.Col3
WHERE t1.Col1 IS NULL
If you want to compare based on single column, then you can do something like this:
SELECT ID FROM B LEFT JOIN A ON B.ID = A.ID WHERE A.ID IS NULL;
The above query will give you the list of records that are not present in A but in B.
Instead if you want to compare the entire row, you can use the following approach:
SELECT COUNT(*) FROM B;
SELECT COUNT(*) FROM A;
SELECT COUNT(*) FROM (
SELECT * FROM B UNION SELECT * FROM A
)
If all the queries returns the same count then you can assume that both the tables are exactly equal.
I have 1 table with data thus:
Col1 Col2
------- --------
Admin001 A
Admin001 B
Admin002 C
Admin002 C
Admin003 A
Admin003 C
I need to find all instances of Col2 values with 'A' immediately followed by 'B'. 'A' followed by any other symbol does not count. Is there a way to use SQL to accomplish this?
Environment is DB2 LUW v9.5
Update:
How can I do this if I make the table like below?
Col1 Col2 Col3
---- ------- --------
1 Admin001 A
2 Admin002 C
3 Admin002 C
4 Admin003 A
5 Admin003 C
6 Admin001 B
7 Admin001 A
8 Admin001 C
9 Admin001 B
Given that there is no implicit ordering of a set, then no, there isn't any reliable way to do this. Your data will need to be ordered (perhaps by a third column, or by column 1) for this to make any sense.
SELECT DISTINCT T1.Col2
FROM Table T1 INNER JOIN Table T2
ON T2.Col2 = T1.Col2 AND T2.Col1 = (T1.Col1 + 1)
WHERE T1.Col3 = 'A' AND T2.Col3 = 'B'
Update: As mentioned by Peter Lang, below, this will not work if the sequence in Col1 is interrupted. This version handles that situation and is more guaranteed to produce the correct result although if you're 100% certain the sequence will not be interrupted (that is, if you generate the sequence yourself in the same transaction as the analysis) the first should be faster:
SELECT DISTINCT T1.Col2
FROM Table T1 INNER JOIN Table T2
ON T2.Col2 = T1.Col2
AND T2.Col1 = (SELECT MIN(Col1) FROM Table T3 WHERE T3.Col1 > T1.Col1)
WHERE T1.Col3 = 'A' AND T2.Col3 = 'B'
It looks like you're trying to find out who's grade dropped from A to B, so we'll also assume that you want the results where B follows A for the same admin.
SELECT DISTINCT t1.Col2
FROM table t1
INNER JOIN table t2 ON t1.Col2 = t2.Col2
LEFT OUTER JOIN table t3 ON t1.Col2 = t3.Col2
AND t3.Col1 < t2.Col1 AND t3.Col1 > t1.Col1
WHERE t1.Col3 = 'A'
AND t2.Col3 = 'B' AND t2.Col1 > t1.Col1
AND t3.Col1 IS NULL
This yields any admin who has 'A' followed by 'B'.
The INNER JOIN and the first two expressions in the WHERE clause finds all records where 'B' occurs after 'A'. The left OUTER join and the last expression in the WHERE clause finds all records where there are grades between the A and B, and only takes the records without.
You asked to get these results, one per row, like this:
Col1 Col2 Col3
---- ------- --------
1 Admin001 A
6 Admin001 B
I'm going to adapt the above query the easy way.
I'll simply get the A records, get the B records, and union them:
(SELECT t1.Col1, t1.Col2, t1.Col3
FROM table t1
INNER JOIN table t2 ON t1.Col2 = t2.Col2
LEFT OUTER JOIN table t3 ON t1.Col2 = t3.Col2
AND t3.Col1 < t2.Col1 AND t3.Col1 > t1.Col1
WHERE t1.Col3 = 'A'
AND t2.Col3 = 'B' AND t2.Col1 > t1.Col1
AND t3.Col1 IS NULL)
UNION
(SELECT t2.Col1, t2.Col2, t2.Col3
FROM table t1
INNER JOIN table t2 ON t1.Col2 = t2.Col2
LEFT OUTER JOIN table t3 ON t1.Col2 = t3.Col2
AND t3.Col1 < t2.Col1 AND t3.Col1 > t1.Col1
WHERE t1.Col3 = 'A'
AND t2.Col3 = 'B' AND t2.Col1 > t1.Col1
AND t3.Col1 IS NULL)
ORDER BY Col2, Col1
Notice that we're ordering by Col2 first, then Col1. You may also get more than one set of records for each user.
How are you sorting the columns? If you aren't sorting them, you could get different results each time, as sometimes A would follow B, and sometimes B would follow A. If you are sorting them, you may be able to use an 'exists' test with the sorting expression.
There is no general method of getting the next (or previous) row in SQL, but many implementations provide their own built-in functions to help with that kind of thing. Unfortunately I'm not familiar with DB2.
This query assumes that col1 is some sort of sequence or timestamp for each row. Without it, there's no way to determine if A happened before or after B.
WITH sorted AS
(SELECT col1, col2, col3, ROWNUMBER()
OVER (PARTITION BY col2 ORDER BY col1) AS col4
FROM sometable
)
SELECT a.col1, a.col2, a.col3, b.col1, b.col3
FROM sorted a INNER JOIN sorted b
ON a.col2 = b.col2
WHERE a.col3 = 'A' AND b.col3 = 'B'
AND b.col4 = a.col4 + 1
;
I think the following should work, assuming your updated table layout with 3 columns. (Otherwise it's impossible, because no ordering is available):
select t1.col2
from yourtable t1, yourtable t2
where t1.col3 = 'A'
and t2.col3 = 'B'
and t1.col1 + 1 = t2.col1;