I have been facing error in MS Access and error is "The number of columns in the two selected tables or queries of a Union query do not match."
Here is my SQL query:
SELECT sale_head.suppliername AS sale_head_suppliername,
sale_head.invoiceno AS sale_head_invoiceno, sale_head.invoicedate,
sale_details.invoiceno AS sale_details_invoiceno, sale_details.suppliername AS sale_details_suppliername,
sale_details.product_code, sale_details.qty, sale_details.totalkg, sale_details.Rate, sale_details.subtotal FROM sale_head
INNER JOIN sale_details ON sale_head.[invoiceno] = sale_details.[invoiceno]
UNION ALL select 'Total', sum(sale_details.subtotal) from sale_details
WHERE (((sale_head.suppliername)='Ramkrishna Creation'));
Am I missing something ? If yes please do let me know.
When you union two or more queries together each query should have the same columns of data with same data type for example :
SELECT Name,LastName,SUM(Salary) FROM tabel1
UNION
SELECT Text1,Text2,SomeMoney FROM table2
is valid (assuming that Name and Text1,LastName and Text2 and Sum of salary and SomeMoney have the same data type but :
SELECT Name,LastName,SUM(Salary) FROM tabel1
UNION
SELECT Text1,SomeMoney FROM table2
(cloumns count mismatch)or
SELECT Name,LastName,SUM(Salary) FROM tabel1
UNION
SELECT Text1,SomeMoney,Text2 FROM table2
(data type mismatch)are not valid union statements.
UPDATE : My answer is according to SQL Standard Definition of Union Statement which states :
The UNION operator is used to combine the
result-set of two or more SELECT statements.
Notice that each SELECT statement within the UNION must have the same
number of columns. The columns must also have similar data types.
Also, the columns in each SELECT statement must be in the same order.
In a UNION, both datasets must have the same number of columns but they don't need to be the same datatype
All queries in a UNION operation must request the same number of fields; however, the fields do not have to be of the same size or data type.
UNION Operation (Microsoft Access SQL)
I've been trying for a few hours (probably more than I needed to) to figure out the best way to write an update sql query that will dissallow duplicates on the column I am updating.
Meaning, if TableA.ColA already has a name 'TEST1', then when I'm changing another record, then I simply can't pick a value for ColA to be 'TEST1'.
It's pretty easy to simply just separate the query into a select, and use a server layer code that would allow conditional logic:
SELECT ID, NAME FROM TABLEA WHERE NAME = 'TEST1'
IF TableA.recordcount > 0 then
UPDATE SET NAME = 'TEST1' WHERE ID = 1234
END IF
But I'm more interested to see if these two queries can be combined into a single query.
I am using Oracle to figure things out, but I'd love to see a SQL Server query as well. I figured a MERGE statement can work, but for obvious reasons you can't have the clause:
..etc.. WHEN NOT MATCHED UPDATE SET ..etc.. WHERE ID = 1234
AND you can't update a column if it's mentioned in the join (oracle limitation but not limited to SQL Server)
ALSO, I know you can put a constraint on a column that prevents duplicate values, but I'd be interested to see if there is such a query that can do this without using constraint.
Here is an example start-up attempt on my end just to see what I can come up with (explanations on it failed is not necessary):
ERROR: ORA-01732: data manipulation operation not legal on this view
UPDATE (
SELECT d.NAME, ch.NAME FROM (
SELECT 'test1' AS NAME, '2722' AS ID
FROM DUAL
) d
LEFT JOIN TABLEA a
ON UPPER(a.name) = UPPER(d.name)
)
SET a.name = 'test2'
WHERE a.name is null and a.id = d.id
I have tried merge, but just gave up thinking it's not possible. I've also considered not exists (but I'd have to be careful since I might accidentally update every other record that doesn't match a criteria)
It should be straightforward:
update personnel
set personnel_number = 'xyz'
where person_id = 1001
and not exists (select * from personnel where personnel_number = 'xyz');
If I understand correctly, you want to conditionally update a field, assuming the value is not found. The following query does this. It should work in both SQL Server and Oracle:
update table1
set name = 'Test1'
where (select count(*) from table1 where name = 'Test1') > 0 and
id = 1234
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).
What is the difference between the EXISTS and IN clause in SQL?
When should we use EXISTS, and when should we use IN?
The exists keyword can be used in that way, but really it's intended as a way to avoid counting:
--this statement needs to check the entire table
select count(*) from [table] where ...
--this statement is true as soon as one match is found
exists ( select * from [table] where ... )
This is most useful where you have if conditional statements, as exists can be a lot quicker than count.
The in is best used where you have a static list to pass:
select * from [table]
where [field] in (1, 2, 3)
When you have a table in an in statement it makes more sense to use a join, but mostly it shouldn't matter. The query optimiser should return the same plan either way. In some implementations (mostly older, such as Microsoft SQL Server 2000) in queries will always get a nested join plan, while join queries will use nested, merge or hash as appropriate. More modern implementations are smarter and can adjust the plan even when in is used.
EXISTS will tell you whether a query returned any results. e.g.:
SELECT *
FROM Orders o
WHERE EXISTS (
SELECT *
FROM Products p
WHERE p.ProductNumber = o.ProductNumber)
IN is used to compare one value to several, and can use literal values, like this:
SELECT *
FROM Orders
WHERE ProductNumber IN (1, 10, 100)
You can also use query results with the IN clause, like this:
SELECT *
FROM Orders
WHERE ProductNumber IN (
SELECT ProductNumber
FROM Products
WHERE ProductInventoryQuantity > 0)
Based on rule optimizer:
EXISTS is much faster than IN, when the sub-query results is very large.
IN is faster than EXISTS, when the sub-query results is very small.
Based on cost optimizer:
There is no difference.
I'm assuming you know what they do, and thus are used differently, so I'm going to understand your question as: When would it be a good idea to rewrite the SQL to use IN instead of EXISTS, or vice versa.
Is that a fair assumption?
Edit: The reason I'm asking is that in many cases you can rewrite an SQL based on IN to use an EXISTS instead, and vice versa, and for some database engines, the query optimizer will treat the two differently.
For instance:
SELECT *
FROM Customers
WHERE EXISTS (
SELECT *
FROM Orders
WHERE Orders.CustomerID = Customers.ID
)
can be rewritten to:
SELECT *
FROM Customers
WHERE ID IN (
SELECT CustomerID
FROM Orders
)
or with a join:
SELECT Customers.*
FROM Customers
INNER JOIN Orders ON Customers.ID = Orders.CustomerID
So my question still stands, is the original poster wondering about what IN and EXISTS does, and thus how to use it, or does he ask wether rewriting an SQL using IN to use EXISTS instead, or vice versa, will be a good idea?
EXISTS is much faster than IN when the subquery results is very large.
IN is faster than EXISTS when the subquery results is very small.
CREATE TABLE t1 (id INT, title VARCHAR(20), someIntCol INT)
GO
CREATE TABLE t2 (id INT, t1Id INT, someData VARCHAR(20))
GO
INSERT INTO t1
SELECT 1, 'title 1', 5 UNION ALL
SELECT 2, 'title 2', 5 UNION ALL
SELECT 3, 'title 3', 5 UNION ALL
SELECT 4, 'title 4', 5 UNION ALL
SELECT null, 'title 5', 5 UNION ALL
SELECT null, 'title 6', 5
INSERT INTO t2
SELECT 1, 1, 'data 1' UNION ALL
SELECT 2, 1, 'data 2' UNION ALL
SELECT 3, 2, 'data 3' UNION ALL
SELECT 4, 3, 'data 4' UNION ALL
SELECT 5, 3, 'data 5' UNION ALL
SELECT 6, 3, 'data 6' UNION ALL
SELECT 7, 4, 'data 7' UNION ALL
SELECT 8, null, 'data 8' UNION ALL
SELECT 9, 6, 'data 9' UNION ALL
SELECT 10, 6, 'data 10' UNION ALL
SELECT 11, 8, 'data 11'
Query 1
SELECT
FROM t1
WHERE not EXISTS (SELECT * FROM t2 WHERE t1.id = t2.t1id)
Query 2
SELECT t1.*
FROM t1
WHERE t1.id not in (SELECT t2.t1id FROM t2 )
If in t1 your id has null value then Query 1 will find them, but Query 2 cant find null parameters.
I mean IN can't compare anything with null, so it has no result for null, but EXISTS can compare everything with null.
If you are using the IN operator, the SQL engine will scan all records fetched from the inner query. On the other hand if we are using EXISTS, the SQL engine will stop the scanning process as soon as it found a match.
IN supports only equality relations (or inequality when preceded by NOT).
It is a synonym to =any / =some, e.g
select *
from t1
where x in (select x from t2)
;
EXISTS supports variant types of relations, that cannot be expressed using IN, e.g. -
select *
from t1
where exists (select null
from t2
where t2.x=t1.x
and t2.y>t1.y
and t2.z like '℅' || t1.z || '℅'
)
;
And on a different note -
The allegedly performance and technical differences between EXISTS and IN may result from specific vendor's implementations/limitations/bugs, but many times they are nothing but myths created due to lack of understanding of the databases internals.
The tables' definition, statistics' accuracy, database configuration and optimizer's version have all impact on the execution plan and therefore on the performance metrics.
The Exists keyword evaluates true or false, but IN keyword compare all value in the corresponding sub query column.
Another one Select 1 can be use with Exists command. Example:
SELECT * FROM Temp1 where exists(select 1 from Temp2 where conditions...)
But IN is less efficient so Exists faster.
I think,
EXISTS is when you need to match the results of query with another subquery.
Query#1 results need to be retrieved where SubQuery results match. Kind of a Join..
E.g. select customers table#1 who have placed orders table#2 too
IN is to retrieve if the value of a specific column lies IN a list (1,2,3,4,5)
E.g. Select customers who lie in the following zipcodes i.e. zip_code values lies in (....) list.
When to use one over the other... when you feel it reads appropriately (Communicates intent better).
As per my knowledge when a subquery returns a NULL value then the whole statement becomes NULL. In that cases we are using the EXITS keyword. If we want to compare particular values in subqueries then we are using the IN keyword.
Which one is faster depends on the number of queries fetched by the inner query:
When your inner query fetching thousand of rows then EXIST would be better choice
When your inner query fetching few rows, then IN will be faster
EXIST evaluate on true or false but IN compare multiple value. When you don't know the record is exist or not, your should choose EXIST
Difference lies here:
select *
from abcTable
where exists (select null)
Above query will return all the records while below one would return empty.
select *
from abcTable
where abcTable_ID in (select null)
Give it a try and observe the output.
The reason is that the EXISTS operator works based on the “at least found” principle. It returns true and stops scanning table once at least one matching row found.
On the other hands, when the IN operator is combined with a subquery, MySQL must process the subquery first, and then uses the result of the subquery to process the whole query.
The general rule of thumb is that if the subquery contains a large
volume of data, the EXISTS operator provides a better performance.
However, the query that uses the IN operator will perform faster if
the result set returned from the subquery is very small.
In certain circumstances, it is better to use IN rather than EXISTS. In general, if the selective predicate is in the subquery, then use IN. If the selective predicate is in the parent query, then use EXISTS.
https://docs.oracle.com/cd/B19306_01/server.102/b14211/sql_1016.htm#i28403
My understand is both should be the same as long as we are not dealing with NULL values.
The same reason why the query does not return the value for = NULL vs is NULL.
http://sqlinthewild.co.za/index.php/2010/02/18/not-exists-vs-not-in/
As for as boolean vs comparator argument goes, to generate a boolean both values needs to be compared and that is how any if condition works.So i fail to understand how IN and EXISTS behave differently
.
If a subquery returns more than one value, you might need to execute the outer query- if the values within the column specified in the condition match any value in the result set of the subquery. To perform this task, you need to use the in keyword.
You can use a subquery to check if a set of records exists. For this, you need to use the exists clause with a subquery. The exists keyword always return true or false value.
I believe this has a straightforward answer. Why don't you check it from the people who developed that function in their systems?
If you are a MS SQL developer, here is the answer directly from Microsoft.
IN:
Determines whether a specified value matches any value in a subquery or a list.
EXISTS:
Specifies a subquery to test for the existence of rows.
I found that using EXISTS keyword is often really slow (that is very true in Microsoft Access).
I instead use the join operator in this manner :
should-i-use-the-keyword-exists-in-sql
If you can use where in instead of where exists, then where in is probably faster.
Using where in or where exists
will go through all results of your parent result. The difference here is that the where exists will cause a lot of dependet sub-queries. If you can prevent dependet sub-queries, then where in will be the better choice.
Example
Assume we have 10,000 companies, each has 10 users (thus our users table has 100,000 entries). Now assume you want to find a user by his name or his company name.
The following query using were exists has an execution of 141ms:
select * from `users`
where `first_name` ='gates'
or exists
(
select * from `companies`
where `users`.`company_id` = `companies`.`id`
and `name` = 'gates'
)
This happens, because for each user a dependent sub query is executed:
However, if we avoid the exists query and write it using:
select * from `users`
where `first_name` ='gates'
or users.company_id in
(
select id from `companies`
where `name` = 'gates'
)
Then depended sub queries are avoided and the query would run in 0,012 ms
I did a little exercise on a query that I have recently been using. I originally created it with INNER JOINS, but I wanted to see how it looked/worked with EXISTS. I converted it. I will include both version here for comparison.
SELECT DISTINCT Category, Name, Description
FROM [CodeSets]
WHERE Category NOT IN (
SELECT def.Category
FROM [Fields] f
INNER JOIN [DataEntryFields] def ON f.DataEntryFieldId = def.Id
INNER JOIN Section s ON f.SectionId = s.Id
INNER JOIN Template t ON s.Template_Id = t.Id
WHERE t.AgencyId = (SELECT Id FROM Agencies WHERE Name = 'Some Agency')
AND def.Category NOT IN ('OFFLIST', 'AGENCYLIST', 'RELTO_UNIT', 'HOSPITALS', 'EMS', 'TOWCOMPANY', 'UIC', 'RPTAGENCY', 'REP')
AND (t.Name like '% OH %')
AND (def.Category IS NOT NULL AND def.Category <> '')
)
ORDER BY 1
Here are the statistics:
Here is the converted version:
SELECT DISTINCT cs.Category, Name, Description
FROM [CodeSets] cs
WHERE NOT Exists (
SELECT * FROM [Fields] f
WHERE EXISTS (SELECT * FROM [DataEntryFields] def
WHERE def.Id = f.DataEntryFieldId
AND def.Category NOT IN ('OFFLIST', 'AGENCYLIST', 'RELTO_UNIT', 'HOSPITALS', 'EMS', 'TOWCOMPANY', 'UIC', 'RPTAGENCY', 'REP')
AND (def.Category IS NOT NULL AND def.Category <> '')
AND def.Category = cs.Category
AND EXISTS (SELECT * FROM Section s
WHERE f.SectionId = s.Id
AND EXISTS (SELECT * FROM Template t
WHERE s.Template_Id = t.Id
AND EXISTS (SELECT * FROM Agencies
WHERE Name = 'Some Agency' and t.AgencyId = Id)
AND (t.Name like '% OH %')
)
)
)
)
ORDER BY 1
The results, at least to me, were unimpressive.
If I were more technically knowledgeable about how SQL works, I could give you an answer, but take this example as you may and make your own conclusion.
The INNER JOIN and IN () is easier to read, however.
EXISTS Is Faster in Performance than IN.
If Most of the filter criteria is in subquery then better to use IN and If most of the filter criteria is in main query then better to use EXISTS.
If you are using the IN operator, the SQL engine will scan all records fetched from the inner query. On the other hand if we are using EXISTS, the SQL engine will stop the scanning process as soon as it found a match.