I have to create a view from more than one table in an MS SQL Server database, but I am not able to get the correct syntax for the same.
You'll have to provide more information about how you are looking to return data from more than one table. Typically you use JOINs:
CREATE VIEW your_view_vw AS
SELECT *
FROM TABLE_A a
JOIN TABLE_B b ON b.pk = a.fk
...where fk stands for "Foreign Key", and pk stands for "Primary Key" - assuming these constraints are in place. Maybe you need to use a Cross join instead? Here's a great visual representation of JOINs visually.
Reference:
CREATE VIEW
You do this with JOINs, just like you would with a regular query.
If you can write a query that gets you the data, you should be able to write view nearly the exact same way.
Post what you have.
example
create view ViewCustomerOrders
as
select * from Customer c
join Order o on o.CustomerID = c.CustomerID
create view viewname
as
select * from table a
join table b on b.col2 = a.col2
create view view_name
as
select * from table_A a
join table_B b on a.column_id = b.column_id
Related
I am trying to build hierarchies by nesting queries on the same table in MS SQL Server 2014.
To give an example of what I am trying to achieve:
I have a table 'employees' whith the following columns:
[ID],[First Name],[Last Name],[ReportsTo]
{1},{John},{Doe},{2}
{2},{Mary},{Miller},{NULL}
I am trying to build a statement, where I join the employees table with itself and where I build a hierarchy with the boss on top.
Expected Result:
[Employee],[Boss]
{Miller,Mary},{NULL}
{Doe, John},{Miller,Mary}
I apologize, if this is a stupid question, but I fail to create a working nested query.
Could you please help me with that?
Thank you very much in advance
Based on the intended results, it looks like what you essentially want is a list of employees. So let's start with that:
SELECT LastName, FirstName, ReportsTo FROM Employees
This gives you the list, so you now have the objects you're looking for. But you need to fill out more data. You want to follow ReportsTo and show data from the record to which that points as well. This would be done exactly as it would if the foreign key pointed to a different table. (The only difference from being the same table is that you must use table aliases in the query, since you're including the same table twice.)
So let's start by joining the table:
SELECT e.LastName, e.FirstName, e.ReportsTo
FROM Employees e
LEFT OUTER JOIN Employees b on e.ReportsTo = b.ID
The results should still be the same, but now you have more data to select from. So you can add the new columns to the SELECT clause:
SELECT
e.LastName AS EmployeeLastName,
e.FirstName AS EmployeeFirstName,
b.LastName AS BossLastName,
b.FirstName AS BossFirstName
FROM Employees e
LEFT OUTER JOIN Employees b on e.ReportsTo = b.ID
It's a join like any other, it just happens to be a join to the same table.
Stupidly simple question, but I just don't know what to google!
If I create a query like this:
Select id, data
from table1
Now I want to join with table2. I can immediately see that the id column is no longer unique and I have to change it to
table1.id
Is there any smart way (like a keyboard-shortcut) to do this, instead of manually adding table1 to every column? Either before I add the Join to secure that all columns will be unique, or after with suggestions based on the different possible tables.
No, there is no helper.
But do not you can alias the table name:
select x.Col1, y.Col2
from ALongTableName x
inner join AReallyReallyLongTableName y on x.Id = y.OtherId
which can also make queries clearer, and is very much necessary when doing self joins.
First of all, you should start using aliases:
SQL aliases are used to give a database table, or a column in a table,
a temporary name.
Basically aliases are created to make column names more readable.
This will narrow down your problem and make your code maintenance easier. If that's not enough, I guess you could start using auto-completion tools, such as these:
SQL Complete
SQL Prompt
ApexSQL Complete
These have your desired functionality, however, they do not always work as expected (at least for me).
Oh! You can use alias table name. Like this:
SELECT A.ID, A.data
FROM TableA A
INNER JOIN TableB B
ON A.ID = B.ID
You just only use A. or B. if two table have same this column selected. If they different, you don't need: Like this:
SELECT A.ID, data -- if Table B not have column data
FROM TableA A
INNER JOIN TableB B
ON A.ID = B.ID
Or:
Select A.*, B.ID
FROM TableA A
INNER JOIN TableB B
ON A.ID = B.ID
I created a view in sql server 2012, such as:
create myview as
select mytable2.name
from mytable1 t1
join myTable2 t2
on t1.id = t2.id
I want that join table1 and table2 will be with correct index (id), but when I do:
select * from myview
where name = 'abcd'
I want that the last select will be with index of column 'name'.
What is the correct syntax in sql server with hints (tuning), that do the best run, as I have described?
I want to force using of index for join purpose only (the column = id), and forcing index name when doing:
select name from myview
where name = 'abcd'.
Something like
create myview as
select mytable2.name
/* index hint name on column name */
from mytable1 t1
join myTable2 t2
/* index hint name on column id - just for join */
on t1.id = t2.id
I don't want to force end-user that uses the view add hint when doing the view - just bring him the view as his with proper index hints.
(or, if it is not possible - how can I do that).
Need samples, please.
Thanks :)
I reckon creating an Index on the Name column would use the index, when selecting from view with the above shown where clause, you dont have to explicitly give any query hints to make that view use the index.
Index should be something like...
Index
CREATE NONCLUSTERED INDEX [IX_MyTable1_Name]
ON [dbo].[myTable2] ([CompanyName] ASC)
GO
View Definition
CREATE VIEW myview
AS
SELECT t2.name --<-- Use alias here since you have alised your table in from clause
FROM mytable1 t1
INNER JOIN myTable2 t2 ON t1.id = t2.id
Indexes in SqlServer are built from two sets of columns.
Create index IX on table B (Filter Columns,Sorting Columns) INCLUDE (Additional columns to be included).
And when selecting from views, the optimizer will incorporate indexes on the referenced tables.
The first set is the indexing table itself. Best practice is to place the columns by which you filter first, and then the columns by which you sort.
The second set (Include), are additional columns you add to the indexing table, so all the data you require is in the index (to prevent key look ups - dpending on your table design).
In your case, the order will be
1) Go to MyTable2 by name, and get all of the matching ID's.
2) With the Id's from step 1, find the matching ID's in Mytable1
Your indexes should be :
1) An index on Table2(Name,ID) or Table2(Name)Include(ID)
2) An index on Table1(ID)
There shouldn't be any hint used in this case.
And in general, you should avoid using hints.
I have this ugly source data with two columns, let's call them EmpID and SomeCode. Generally EmpID maps to the EmployeeListing table. But sometimes, people are entering the Employee IDs in the SomeCode field.
The person previously running this report in Excel 'solved' this problem by performing multiple vlookups with if statements, as well as running some manual checks to ensure results were accurate. As I'm moving these files to Access I am not sure how best to handle this scenario.
Ideally, I'm hoping to tell my queries to do a Left Join on SomeCode if EmpID is null, otherwise Left Join on EmpID
Unfortunately, there's no way for me to force validation or anything of the sort in the source data.
Here's the full SQL query I'm working on:
SELECT DDATransMaster.Fulfillment,
DDATransMaster.ConfirmationNumber,
DDATransMaster.PromotionCode,
DDATransMaster.DirectSellerNumber,
NZ([DDATransMaster]![DirectSellerNumber],[DDATransMaster]![PromotionCode]) AS EmpJoin,
EmployeeLookup.ID AS EmpLookup,
FROM FROM DDATransMaster
LEFT JOIN EmployeeLookup ON NZ([DDATransMaster]![DirectSellerNumber],[DDATransMaster]![PromotionCode]) = EmployeeLookup.[Employee #])
You can create a query like this:
SELECT
IIf(EmpID Is Null, SomeCode, EmpID) AS join_field,
field2,
etc
FROM YourTable
Or if the query will always be used within an Access session, Nz is more concise.
SELECT
Nz(EmpID, SomeCode) AS join_field,
field2,
etc
FROM YourTable
When you join that query to your other table, the Access query designer can represent the join between join_field and some matching field in the other table. If you were to attempt the IIf or Nz as part of the join's ON clause, the query designer can't display the join correctly in Design View --- it could still work, but may not be as convenient if you're new to Access SQL.
See whether this SQL gives you what you want.
SELECT
dda.Fulfillment,
dda.ConfirmationNumber,
dda.PromotionCode,
dda.DirectSellerNumber,
NZ(dda.DirectSellerNumber,dda.PromotionCode) AS EmpJoin,
el.ID AS EmpLookup
FROM
DDATransMaster AS dda
LEFT JOIN EmployeeLookup AS el
ON NZ(dda.DirectSellerNumber,dda.PromotionCode) = el.[Employee #])
But I would use the Nz part in a subquery.
SELECT
sub.Fulfillment,
sub.ConfirmationNumber,
sub.PromotionCode,
sub.DirectSellerNumber,
sub.EmpJoin,
el.ID AS EmpLookup
FROM
(
SELECT
Fulfillment,
ConfirmationNumber,
PromotionCode,
DirectSellerNumber,
NZ(DirectSellerNumber,PromotionCode) AS EmpJoin
FROM DDATransMaster
) AS sub
LEFT JOIN EmployeeLookup AS el
ON sub.EmpJoin = el.[Employee #])
What about:
LEFT JOIN EmployeeListing ON NZ(EmpID, SomeCode)
as your join, nz() uses the second parameter if the first is null, I'm not 100% sure this sort of join works in access. Worth 20 seconds to try though.
Hope it works.
You Could use a Union:
SELECT DDATransMaster.Fulfillment,
DDATransMaster.ConfirmationNumber,
DDATransMaster.PromotionCode,
DDATransMaster.DirectSellerNumber,
EmployeeLookup.ID AS EmpLookup
FROM DDATransMaster
LEFT JOIN EmployeeLookup ON
DDATransMaster.DirectSellerNumber = EmployeeLookup.[Employee #]
where DDATransMaster.DirectSellerNumber IS NOT NULL
Union
SELECT DDATransMaster.Fulfillment,
DDATransMaster.ConfirmationNumber,
DDATransMaster.PromotionCode,
DDATransMaster.DirectSellerNumber,
EmployeeLookup.ID AS EmpLookup
FROM DDATransMaster
LEFT JOIN EmployeeLookup ON
DDATransMaster.PromotionCode = EmployeeLookup.[Employee #]
where DDATransMaster.DirectSellerNumber IS NULL;
I have a stored procedure that is heavily using multiple level of nested dervied tables. I am just wondering what is the best method of debugging this type of queries where you can look into what is coming from the inner derived tables etc? Any thoughts?
Sometimes, I'll at least temporarily pull those derived tables out into a table variable or temp table so I can get a better look at what's going on.
So, in an over-simplified example:
select *
from table_a
inner join (select * from table_b) b
...
would become
select *
into #tempb
from table_b
select * from #tempb /* for debugging purposes */
select *
from table_a
inner join #tempb b
...