I need to compare and match the longest match of two strings in two different tables and update one values if there is a closest match.
Table 1 Table 2
stack1 stack2
ABCDEFG ABC
GHIJKLM ABCDE
PQRSUVW ABCDEF
I need to compare these two tables and match the closeet one and update Table 1 first row as ABCDEF the closest match, Please can anyone help me out. I am stuck here.
Here is my query
UPDATE table1 A
SET A.stack1 = (SELECT DISTINCT B.stack2
FROM table2 B
WHERE A.stack1 LIKE CONCAT(B.stack2,'%'))
WHERE name = 'name';
with this query am getting an error called
ORA-01427: single-row subquery returns more than one row
You need to make the subquery return only a single match (the longest one). In your case MAX should do that.
UPDATE table1 A
SET A.stack1 = (SELECT Max( B.stack2 )
FROM table2 B
WHERE A.stack1 LIKE CONCAT(B.stack2,'%'))
WHERE name = 'name';
Also, you should think about the case where nothing matches.
The ORA-01427 error is saying the subquery is returning more than one value -- even with the DISTINCT.
You need to correct the case(s) that are returning more than one distinct value. That could be with an aggregate function, like MAX or MIN, but without details I hesitate to make that recommendation.
Related
I want to select row IDs associated with distinct column combinations in the remainder of a table. For instance, if the distinct rows are
I want to get the row IDs associated with each row. I can't query for distinct IDs since they are the row's primary key (and hence are all distinct).
So far I have:
SELECT e.ID
FROM E_UPLOAD_TEST e
INNER JOIN (
SELECT DISTINCT WHAT, MATERIALS, ERROR_FIELD, UNITS, SEASONALITY, DATA_TYPE, DETAILS, METHODS, DATA_FORMAT
FROM E_UPLOAD_TEST) c
ON e.WHAT = c.WHAT AND e.MATERIALS = c.MATERIALS AND e.ERROR_FIELD = c.ERROR_FIELD AND e.DATA_TYPE = c.DATA_TYPE AND e.METHODS = c.METHODS AND e.DATA_FORMAT = c.DATA_FORMAT;
which runs but doesn't return anything. Am I missing a GROUP BY and/or MIN() statement?
#serg is correct. Every single row in your example has at least one column value that is null. That means that no row will match your join condition. That is why your query results in no rows found.
Modifying your condition might get you what you want so long has your data isn't changing frequently. If it is changing frequently, then you probably want a single query for the entire job otherwise you'll have to set your transaction so that it is immune to data changes.
An example of such a condition change is this:
( (e.WHAT is null and c.WHAT is null) or (e.WHAT = c.WHAT) )
But such a change makes sense only if two rows having a null value in the same column means the same thing for both rows and it has to mean the same thing as time marches on. What "WHAT is null" means today might not be the same thing tomorrow. And that is probably why C. J. Date hates nulls so much.
Instead of comparing, use the decode function which compares two null values correctly.
e.WHAT = c.WHAT -> DECODE(e.WHAT, c.WHAT, 1) = 1
I am trying to write a query where I need to check whether a value is not present in an array of strings returned by another nested query how can I do that,
For example I have to check whether,
1234 is present in [abc_1234,fgh_12345,ghi_5343]
Hence 1234 is present in string abc_1234 so I will not select 1234.
I hope I understand your request correctly. You have a query returning strings, e.g. 'abc_1234' and 'fgh_12345'. You have a table with values, e.g. '1234'. You want to select rows from the table where the value is not part of any of the strings of the existing query.
This is where the anti-join pattern comes into play. You outer-join the undesired rows, so all rows that found no partner are the desired ones:
select *
from mytable m
left join (<your query here>) q on instr(q.string, m.value) > 0
where q.string is null;
(Instead of INSTR you can also use LIKE: on q.string like '%' || m.value || '%'. It should not matter which of the string operations you choose.)
I am just learning SQL, and I'm wondering what the difference is between the following lines:
WHERE s.parent IN (SELECT l.parent .....)
versus
WHERE s.parent = (SELECT l.parent .....)
IN
will not generate an error if you have multiple results on the subquery. Allows to have more than one value in the result returned by the subquery.
=
will generate an error if you have more than one result on the subquery.
SQLFiddle Demo (IN vs =)
when you are using 'IN' it can compare multiple values....like
select * from tablename where student_name in('mari','sruthi','takudu')
but when you are using '=' you can't compare multiple values
select * from tablenamewhere student_name = 'sruthi'
i hope this is the right answer
The "IN" clause is also much much much much slower. If you have many results in the select portion of
IN (SELECT l.parent .....),
it will be extremely inefficient as it actually generates a separate select sql statement for each and every result within the select statement ... so if you return 'Cat', 'Dog', 'Cow'
it will essentially create a sql statement for each result... if you have 200 results... you get the full sql statement 200 times...takes forever... (This was as of a few years ago... maybe imporved by now... but it was horribly slow on big result sets.)
Much more efficient to do an inner join such as:
Select id, parent
from table1 as T
inner join (Select parent from table2) as T2 on T.parent = T2.parent
For future visitors.
Basically in case of equals (just remember that here we are talking like where a.name = b.name), each cell value from table 1 will be compared one by one to each cell value of all the rows from table 2, if it matches then that row will be selected (here that row will be selected means that row from table 1 and table 2) for the overall result set otherwise will not be selected.
Now, in case of IN, complete result set on the right side of the IN will be used for comparison, so its like each value from table 1 will be checked on whether this cell value is present in the complete result set of the IN, if it is present then that value will be shown for all the rows of the IN’s result set, so let say IN result set has 20 rows, so that cell value from table 1 will be present in overall result set 20 times (i.e. that particular cell value will have 20 rows).
For more clarity see below screen shot, notice below that how complete result set from the right of the IN (and NOT IN) is considered in the overall result set; whole emphasis is on the fact that in case comparison using =, matching row from second table is selected, while in case of IN complete result from the second table is selected.
In can match a value with more than one values, in other words it checks if a value is in the list of values so for e.g.
x in ('a', 'b', 'x') will return true result as x is in the the list of values
while = expects only one value, its as simple as
x = y returns false
and
x = x returns true
The general rule of thumb is:
The = expects a single value to compare with. Like this:
WHERE s.parent = 'father_name'
IN is extremely useful in scenarios where = cannot work i.e. scenarios where you need the comparison with multiple values.
WHERE s.parent IN ('father_name', 'mother_name', 'brother_name', 'sister_name')
Hope this is useful!!!
IN
This helps when a subquery returns more than one result.
=
This operator cannot handle more than one result.
Like in this example:
SQL>
Select LOC from dept where DEPTNO = (select DEPTNO from emp where
JOB='MANAGER');
Gives ERROR ORA-01427: single-row subquery returns more than one row
Instead use
SQL>
Select LOC from dept where DEPTNO in (select DEPTNO from emp
where JOB='MANAGER');
1) Sometimes = also used as comparison operator in case of joins which IN doesn't.
2) You can pass multiple values in the IN block which you can't do with =. For example,
SELECT * FROM [Products] where ProductID IN((select max(ProductID) from Products),
(select min(ProductID) from Products))
would work and provide you expected number of rows.However,
SELECT * FROM [Products] where ProductID = (select max(ProductID) from Products)
and ProductID =(select min(ProductID) from Products)
will provide you 'no result'. That means, in case subquery supposed to return multiple number of rows , in that case '=' isn't useful.
I am attempting to use a case statement but keep getting errors. Here's the statement:
select TABLE1.acct,
CASE
WHEN TABLE1.acct_id in (select acct_id
from TABLE2
group by acct_id
having count(*) = 1 ) THEN
(select name
from TABLE3
where TABLE1.acct_id = TABLE3.acct_id)
ELSE 'All Others'
END as Name
from TABLE1
When I replace the TABLE1.acct_id in the THEN expression with a literal value, the query works. When I try to use TABLE1.acct_id from the WHEN part of the query, I get a error saying the result is more than one row. It seems like the THEN expression is ignoring the single value that the WHEN statement was using. No idea, maybe this isn't even a valid use of the CASE statement.
I am trying to see names for accounts that have one entry in TABLE2.
Any ideas would be appreciated, I'm kind of new at SQL.
First, you are missing a comma after TABLE1.acct. Second, you have aliased TABLE1 as acct, so you should use that.
Select acct.acct
, Case
When acct.acct_id in ( Select acct_id
From TABLE2
Group By acct_id
Having Count(*) = 1 )
Then ( Select name
From TABLE3
Where acct.acct_id = TABLE3.acct_id
Fetch First 1 Rows Only)
Else 'All Others'
End as Name
From TABLE1 As acct
As others have said, you should adjust your THEN clause to ensure that only one value is returned. You can do that by add Fetch First 1 Rows Only to your subquery.
Then ( Select name
From TABLE3
Where acct.acct_id = TABLE3.acct_id
Fetch First 1 Rows Only)
Fetch is not accepting in CASE statement - "Keyword FETCH not expected. Valid tokens: ) UNION EXCEPT. "
select name from TABLE3 where TABLE1.acct_id = TABLE3.acct_id
will give you all the names in Table3, which have a accompanying row in Table 1. The row selected from Table2 in the previous line doesn't enter into it.
Must be getting more than one value.
You can replace the body with...
(select count(name) from TABLE3 where TABLE1.acct_id = TABLE3.acct_id)
... to narrow down which rows are returning multiples.
It may be the case that you just need a DISTINCT or a TOP 1 to reduce your result set.
Good luck!
I think that what is happening here is that your case must return a single value because it will be the value for the "name" column. The subquery (select acct_id from TABLE2 group by acct_id having count(*) = 1 ) is OK because it will only ever return one value. (select name from TABLE3 where TABLE1.acct_id= TABLE3.acct_id) could return multiple values depending on your data. The problem is you trying to shove multiple values into a single field for a single row.
The next thing to do would be to find out what data causes multiple rows to be returned by (select name from TABLE3 where TABLE1.acct_id= TABLE3.acct_id), and see if you can further limit this query to only return one row. If need be, you could even try something like ...AND ROWNUM = 1 (for Oracle - other DBs have similar ways of limiting rows returned).
Also what will be the scenarios where this query is used
select * from TableA where exists
(select null from TableB where TableB.Col1=TableA.Col1)
As the query is in an EXISTS then you can return anything. It is not even evaluated.
In fact, you can replace the null with (1/0) and it will not even produce a divide by zero error.
The NULL makes no sense. It's simply bad SQL.
The exists clause is supposed to use SELECT *.
People make up stories about the cost of SELECT *. They claim it does an "extra" metadata query. It doesn't. They claim it's a "macro expansion" and requires lots of extra parse time. It doesn't.
The EXISTS condition is considered "to be met" if the subquery returns at least one row.
The syntax for the EXISTS condition is:
SELECT columns
FROM tables
WHERE EXISTS ( subquery );
Please note that "Select Null from mytable" will return number of rows in mytable but all will contain only one column with null in the cell as the requirement of outer query is just to check whether any row fall in the given given condition like in your case it is "TableB.Col1=TableA.Col1"
you can change null to 1, 0 or any column name available in the table. 1/0 may not be a good idea :)
It's a tacky way of selecting all records in TableA, which have a matching record (Col1=Col1) in TableB. They might equally well have selected '1', or '*', for instance.
A more human-readable way of achieving the same would be
SELECT * FROM TableA WHERE Col1 IN ( SELECT Col1 IN TableB )
Please, please, all ....
EXISTS returns a BOOLEAN i.e. TRUE or FALSE. If the result set is non empty then return TRUE. Correlation of the sub-query is important as in the case above.
i.e Give me all the rows in A where AT LEAST one col1 exists in B.
It does not matter what is in the select list. Its just a matter of style.