Here is my query:
Select a.* from Table1 a, Table2 b
Where
a.tid=b.tid and
b.createddate=(Select max(createddate) from Table2) and
a.tid not in (Select distinct tid from Table3);
The problem is I know this should return some valid output but it does not. The issue us with the last line in the a.tid not in (Select distinct tid from Table3); if I replace Select distinct tid from Table3 with hard coded values like ('T001','T002','T003','T004') then it works fine and returns data.
Whats wrong? Am I missing something? Please help.
Try this:
Select a.* from Table1 a, Table2 b
Where
a.tid=b.tid and
b.createddate=(Select max(createddate) from Table2) and
a.tid not in (Select tid from Table3 where tid is not null);
As all the people in the comments mentioned, if there is at least one row with a null value for tid in table3 you will get no rows returned. This is because to Oracle null is like saying "I don't know what this value is". Oracle can't say with certainty that the value you are searching for is definitely not in your sub-select because it doesn't know what this "not-known" value actually is. Also, the documentation says it works that way:
http://docs.oracle.com/cd/B28359_01/server.111/b28286/conditions013.htm
Another option would be to write the query as:
Select a.* from Table1 a, Table2 b
Where
a.tid=b.tid and
b.createddate=(Select max(createddate) from Table2) and
not exists (Select null from Table3 t3 where t3.tid = a.tid);
The handling of nulls is one of the major differences between not exists and not in.
Your query, slightly rewritten:
Select a.*
from Table1 a join
Table2 b
on a.tid=b.tid
where b.createddate=(Select max(createddate) from Table2) and
a.tid not in (Select distinct tid from Table3)
What this tells me is that the tid with the maximum create date from Table2 is in Table3.
To test this, get the maximum create date from table2. Then get all records in table1 that correspond to this max. You will find that these are also in table3.
If I had to speculate, you might want the max create date per table in Table2, rather than the overall max.
By the way, in Oracle (and most other databases) the distinct in the last subquery is redundant. The database should be smart enough to remove duplicates in this case.
Related
table1 (id, name)
table2 (id, name)
Query:
SELECT name
FROM table2
-- that are not in table1 already
SELECT t1.name
FROM table1 t1
LEFT JOIN table2 t2 ON t2.name = t1.name
WHERE t2.name IS NULL
Q: What is happening here?
A: Conceptually, we select all rows from table1 and for each row we attempt to find a row in table2 with the same value for the name column. If there is no such row, we just leave the table2 portion of our result empty for that row. Then we constrain our selection by picking only those rows in the result where the matching row does not exist. Finally, We ignore all fields from our result except for the name column (the one we are sure that exists, from table1).
While it may not be the most performant method possible in all cases, it should work in basically every database engine ever that attempts to implement ANSI 92 SQL
You can either do
SELECT name
FROM table2
WHERE name NOT IN
(SELECT name
FROM table1)
or
SELECT name
FROM table2
WHERE NOT EXISTS
(SELECT *
FROM table1
WHERE table1.name = table2.name)
See this question for 3 techniques to accomplish this
I don't have enough rep points to vote up froadie's answer. But I have to disagree with the comments on Kris's answer. The following answer:
SELECT name
FROM table2
WHERE name NOT IN
(SELECT name
FROM table1)
Is FAR more efficient in practice. I don't know why, but I'm running it against 800k+ records and the difference is tremendous with the advantage given to the 2nd answer posted above. Just my $0.02.
SELECT <column_list>
FROM TABLEA a
LEFTJOIN TABLEB b
ON a.Key = b.Key
WHERE b.Key IS NULL;
https://www.cloudways.com/blog/how-to-join-two-tables-mysql/
This is pure set theory which you can achieve with the minus operation.
select id, name from table1
minus
select id, name from table2
Here's what worked best for me.
SELECT *
FROM #T1
EXCEPT
SELECT a.*
FROM #T1 a
JOIN #T2 b ON a.ID = b.ID
This was more than twice as fast as any other method I tried.
Watch out for pitfalls. If the field Name in Table1 contain Nulls you are in for surprises.
Better is:
SELECT name
FROM table2
WHERE name NOT IN
(SELECT ISNULL(name ,'')
FROM table1)
You can use EXCEPT in mssql or MINUS in oracle, they are identical according to :
http://blog.sqlauthority.com/2008/08/07/sql-server-except-clause-in-sql-server-is-similar-to-minus-clause-in-oracle/
That work sharp for me
SELECT *
FROM [dbo].[table1] t1
LEFT JOIN [dbo].[table2] t2 ON t1.[t1_ID] = t2.[t2_ID]
WHERE t2.[t2_ID] IS NULL
You can use following query structure :
SELECT t1.name FROM table1 t1 JOIN table2 t2 ON t2.fk_id != t1.id;
table1 :
id
name
1
Amit
2
Sagar
table2 :
id
fk_id
email
1
1
amit#ma.com
Output:
name
Sagar
All the above queries are incredibly slow on big tables. A change of strategy is needed. Here there is the code I used for a DB of mine, you can transliterate changing the fields and table names.
This is the strategy: you create two implicit temporary tables and make a union of them.
The first temporary table comes from a selection of all the rows of the first original table the fields of which you wanna control that are NOT present in the second original table.
The second implicit temporary table contains all the rows of the two original tables that have a match on identical values of the column/field you wanna control.
The result of the union is a table that has more than one row with the same control field value in case there is a match for that value on the two original tables (one coming from the first select, the second coming from the second select) and just one row with the control column value in case of the value of the first original table not matching any value of the second original table.
You group and count. When the count is 1 there is not match and, finally, you select just the rows with the count equal to 1.
Seems not elegant, but it is orders of magnitude faster than all the above solutions.
IMPORTANT NOTE: enable the INDEX on the columns to be checked.
SELECT name, source, id
FROM
(
SELECT name, "active_ingredients" as source, active_ingredients.id as id
FROM active_ingredients
UNION ALL
SELECT active_ingredients.name as name, "UNII_database" as source, temp_active_ingredients_aliases.id as id
FROM active_ingredients
INNER JOIN temp_active_ingredients_aliases ON temp_active_ingredients_aliases.alias_name = active_ingredients.name
) tbl
GROUP BY name
HAVING count(*) = 1
ORDER BY name
See query:
SELECT * FROM Table1 WHERE
id NOT IN (SELECT
e.id
FROM
Table1 e
INNER JOIN
Table2 s ON e.id = s.id);
Conceptually would be: Fetching the matching records in subquery and then in main query fetching the records which are not in subquery.
First define alias of table like t1 and t2.
After that get record of second table.
After that match that record using where condition:
SELECT name FROM table2 as t2
WHERE NOT EXISTS (SELECT * FROM table1 as t1 WHERE t1.name = t2.name)
I'm going to repost (since I'm not cool enough yet to comment) in the correct answer....in case anyone else thought it needed better explaining.
SELECT temp_table_1.name
FROM original_table_1 temp_table_1
LEFT JOIN original_table_2 temp_table_2 ON temp_table_2.name = temp_table_1.name
WHERE temp_table_2.name IS NULL
And I've seen syntax in FROM needing commas between table names in mySQL but in sqlLite it seemed to prefer the space.
The bottom line is when you use bad variable names it leaves questions. My variables should make more sense. And someone should explain why we need a comma or no comma.
I tried all solutions above but they did not work in my case. The following query worked for me.
SELECT NAME
FROM table_1
WHERE NAME NOT IN
(SELECT a.NAME
FROM table_1 AS a
LEFT JOIN table_2 AS b
ON a.NAME = b.NAME
WHERE any further condition);
I want to get a value from an IN subquery with two columns, without needing to do two queries.
Sample:
SELECT * FROM table1 WHERE id IN(SELECT id, flags FROM table2);
Now I want to get flags directly. Is it possible, and if yes, how?
Any help is appreciated :)
It sounds like you are trying to achieve one of two things:
1) Select every field of records in table1 (and the associated table 2 flag) where the record's id is also found in the id column of table2. If that is the case, then yes, a join will accomplish what you want:
SELECT t1.*,
t2.flags
FROM table1 t1
JOIN table2 t2
ON t1.id = t2.id;
Note that JOIN is used here (rather than other types of joins such as LEFT JOIN) because JOIN will return only table1 records with a match in table2.id. LEFT JOIN, on the other hand, would return every table1 record, and table1 ids without a match in table2 would simply have null in the flags column of your returned table.
2) Select every field of records in table1 where the record's id is also found in either the id column of table2 or the flags column of table2. If that is the case, there are a few ways you could get the desired result, but achieving this using a subquery similar to the question
SELECT *
FROM table1
WHERE id IN (SELECT id FROM table2 UNION DISTINCT SELECT flags FROM table2)
You do this using join:
SELECT t1.*, t2.flags
FROM table1 t1 JOIN
table2 t2
ON t1.id = t2.id;
We have records (Table1), who have a workflow (submitted, approved, etc.) that occurs through inserting records in a child table (Table2). For example if the record in Table1 is submitted, a corresponding record in Table2 is inserted that has the workflow status (StatusField), date, and person submitting. When I then try to query Table1 based on its status (e.g. only submitted records), I'm trying to figure out the most efficient way and am unsure. I've tried creating functions where the PK of Table1 is the parameter and then it kicks out the most recent Statusfield from Table2 with a matching FK. I've also tried making a View with the PK of Table2 for the Max PK grouped by FK and then linked via LEFT OUTER JOIN (as there may be no corresponding records in Table2, meaning the status is pending). The way that seems faster is to do a subquery like so:
SELECT a.*
,(SELECT TOP 1 StatusField
FROM Table2 b
WHERE b.FK=a.PK
ORDER BY b.DateField DESC) StatusField
FROM Table1 a
WHERE (SELECT TOP 1 StatusField
FROM Table2 b
WHERE b.FK=a.PK
ORDER BY b.DateField DESC)='Submitted'
I still feel like there is a better way. Any thoughts? If there is a similar question and answer someone can point me to, that would also be awesome. Thank you!
One possible solution (question is tagged MySQL) - use a derived table to obtain the maximum datefield for each fk, then join back to table2 to see if statusfield is submitted....
select a.*
, b.StatusField
from table1 a
join (select fk
, max(datefield) datefield
from table2
group by fk) max on (max.fk = a.fk)
join table2 b on (b.fk = a.fk and b.datefield = max.datefield) and b.StatusField = 'Submitted');
I have two datasets on two seperate servers. They both pull one column of information each.
I would like to build a report showing the values of the rows that only appear in one of the datasets.
From what I have read, it seems I would like to do this on the SQL side, not the reporting side; I am not sure how to do that.
If someone could shed some light on how that is possible, I would really appreciate it.
You can use the NOT EXISTS clause to get the differences between the two tables.
SELECT
Column
FROM
DatabaseName.SchemaName.Table1
WHERE
NOT EXISTS
(
SELECT
Column
FROM
LinkedServerName.DatabaseName.SchemaName.Table2
WHERE
Table1.Column = Table2.Column --looks at equalities, and doesn't
--include them because of the
--NOT EXISTS clause
)
This will show the rows in Table1 that don't appear in Table2. You can reverse the table names to find the rows in Table2 that don't appear in Table1.
Edit: Made an edit to show what the case would be in the event of linked servers. Also, if you wanted to see all of the rows that are not shared in both tables at the same time, you can try something as in the below.
SELECT
Column, 'Table1' TableName
FROM
DatabaseName.SchemaName.Table1
WHERE
NOT EXISTS
(
SELECT
Column
FROM
LinkedServerName.DatabaseName.SchemaName.Table2
WHERE
Table1.Column = Table2.Column --looks at equalities, and doesn't
--include them because of the
--NOT EXISTS clause
)
UNION
SELECT
Column, 'Table2' TableName
FROM
LinkedServerName.DatabaseName.SchemaName.Table2
WHERE
NOT EXISTS
(
SELECT
Column
FROM
DatabaseName.SchemaName.Table1
WHERE
Table1.Column = Table2.Column
)
You can also use a left join:
select a.* from tableA a
left join tableB b
on a.PrimaryKey = b.ForeignKey
where b.ForeignKey is null
This query will return all records from tableA that do not have corresponding records in tableB.
If you want rows that appear in exactly one data set and you have a matching key on each table, then you can use a full outer join:
select *
from table1 t1 full outer join
table2 t2
on t1.key = t2.key
where t1.key is null and t2.key is not null or
t1.key is not null and t2.key is null
The where condition chooses the rows where exactly one match.
The problem with this query, though, is that you get lots of columns with nulls. One way to fix this is by going through the columns one by one in the SELECT clause.
select coalesce(t1.key, t2.key) as key, . . .
Another way to solve this problem is to use a union with a window function. This version brings together all the rows and counts the number of times that key appears:
select t.*
from (select t.*, count(*) over (partition by key) as keycnt
from ((select 'Table1' as which, t.*
from table1 t
) union all
(select 'Table2' as which, t.*
from table2 t
)
) t
) t
where keycnt = 1
This has the additional column specifying which table the value comes from. It also has an extra column, keycnt, with the value 1. If you have a composite key, you would just replace with the list of columns specifying a match between the two tables.
If I run the two statements in batch will they return one table to two to my sqlcommand object with the data merged. What I am trying to do is optimize a search by searching twice, the first time on one set of data and then a second on another. They have the same fields and I’d like to have all the records from both tables show and be added to each other. I need this so that I can sort the data between both sets of data but short of writing a stored procedure I can’t think of a way of doing this.
Eg. Table 1 has columns A and B, Table 2 has these same columns but different data source. I then wan to merge them so that if a only exists in one column it is added to the result set and if both exist it eh tables the column B will be summed between the two.
Please note that this is not the same as a full outer join operation as that does not merge the data.
[EDIT]
Here's what the code looks like:
Select * From
(Select ID,COUNT(*) AS Count From [Table1]) as T1
full outer join
(Select ID,COUNT(*) AS Count From [Table2]) as T2
on t1.ID = T2.ID
Perhaps you're looking for UNION?
IE:
SELECT A, B FROM Table1
UNION
SELECT A, B FROM Table2
Possibly:
select table1.a, table1.b
from table1
where table1.a not in (select a from table2)
union all
select table1.a, table1.b+table2.b as b
from table1
inner join table2 on table1.a = table2.a
edit: perhaps you would benefit from unioning the tables before counting. e.g.
select id, count() as count from
(select id from table1
union all
select id from table2)
I'm not sure if I understand completely but you seem to be asking about a UNION
SELECT A,B
FROM tableX
UNION ALL
SELECT A,B
FROM tableY
To do it, you would go:
SELECT * INTO TABLE3 FROM TABLE1
UNION
SELECT * FROM TABLE2
Provided both tables have the same columns
I think what you are looking for is this, but I am not sure I am understanding your language correctly.
select id, sum(count) as count
from (
select id, count() as count
from table1
union all
select id, count() as count
from table2
) a
group by id