How can i do a very simple join in nette database, resulting in a query like this?
SELECT * FROM Book LEFT OUTER JOIN Author ON Book.author_id = Author.id
I have found endless tutorials on how to join combined with where clausules, order by, group by and what not, but not single tutorial on a simple join like this.
I forgot to specify, I use PHP, so i need something like $context->table('Book')->join('author');, but that of course doesn't work.
Question is already answerred, so I only add one note.
You can't do join using Nette Database, there is no join function. You can enforce join by referencing another table column in order for example, but it's pretty limited. If you need more complex join, you should better use Dibi instead of Nette Database.
You do not need join in this case, Nette provide you relationship between tables, so you can do something like this:
foreach($connection->table('book') as $book){
echo 'Book name: '.$book->name.'<br>'
echo 'Book autor: '.$book->author->name.'<br>'
}
I expect then in book table there is column author_id which is foreign key for author table.
Related
I'm working on this project were I'm using Laravel 8 as my backend frame work and I have to make a self Join, I have tried out this code but it did not work -the first join is the one I tried but failed- :
public function get_all_medical_centers(){
$data= DB:: table('medicalcenters')
->join('medicalcenters','medicalcenters.id',"=",'medicalcenters.parent_id')
->join('countries','medicalcenters.country_id',"=",'countries.id')
->join('states','medicalcenters.country_id',"=",'states.id')
->join('cities','medicalcenters.country_id',"=",'cities.id')
->select('medicalcenters.*', 'countries.name as country_name', 'states.name as state_name', 'cities.name as cities_name')
->get();
return $data;
}
The thing is, in the database the medical centers table has some attributes that are the parent of other attributes and I want to get the name of the parent attribute when previewing the children to also preview the name of its parent and not just the id.
the table diagram:
If you try to self-join a table then you have to give at least one of them an alias, because otherwise, SQL can't know what you are referring to if you select any column from those tables.
To add an alias to your joined table, you can do this:
DB::table('medicalcenters AS medc')
->join('medicalcenters AS self','medc.id',"=",'self.parent_id')
But this is a hacky solution and for normal relational data in Laravel, eloquent models would better.
Edit Why do you need Aliases on self joins:
If you join two tables, lets say: users join posts on users.id = posts.user_id. You have to specify the join condition. Here this is users.id = posts.user_id.
Lets modify this to a self join: users join users on users.id = users.user_id. Here the condition is not clear. Is this users.id or this users.user_id the original table or the self joined table? It's not clear how to join those two tables. So we have to give them different names aka aliases. Like this users as creators join users as subscribers on creators.id = subscribers.user_id.
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
tableA
------
Aprimarykey,
Afield1,
Afield2,
AfieldtoMatch
tableB
------
Bprimarykey,
Bfield1,
Bfield2,
BfieldtoMatch
There is no relationship between tables. What would be the classes and the hbm file look like if I want the following results?
select distinct tableA.Afield1, tableA.Afield2,tableA.AfieldMatch tableB.Bfield1,tableB.Bfield1
from tableA innerjoin tableB on tableA.AfieldtoMatch=tableB.Bmatchfield
Since you want to join, clearly there is some sort of relationship, though abstract.
Stating an SQL query as the intended results leaves the question still open for interpretation. You should probably map the tables each to separate entities, then you can use HQL or LINQ to join on arbitrary columns when you query.
You might also want to look at the <join> element in the reference: http://nhibernate.info/doc/nh/en/index.html#mapping-declaration-join.
Is there any way in MS-Access to update a table where the data is coming from an outer joined dataset or a derived table? I know how to do it in MSSQL, but in Access I always receive an "Operation must use updateable query" error. The table being updated is updateable, the source data is not. After reading up on the error, Microsoft tells me that the error is caused when the query would violate referential integrity. I can assure this dataset will not. This limitation is crippling when trying to update large datasets. I also read that this can supposedly be remedied by enabling cascading updates. If this relationship between my tables is defined in the query only, is this a possibility? So far writing the dataset to a temp table and then inner joining that to the update table is my only solution; that is incredibly clunky. I would like to do something along the lines of this:
UPDATE Table1
LEFT JOIN Table2 ON Table1.Field1=Table2.Field1
WHERE Table2.Field1 IS Null
SET Table1.Field1= Table2.Field2
or
UPDATE Table1 INNER JOIN
(
SELECT Field1, Field2
FROM Table2, Table3
WHERE Field3=’Whatever’
) AS T2 ON Table1.Field1=T2.Field1
SET Table1.Field1= T2.Field2
Update Queries are very problematic in Access as you've been finding out.
The temp table idea is sometimes your only option.
Sometimes using the DISTINCTROW declaration solves the problem (Query Properties -> Unique Records to 'Yes'), and is worth trying.
Another thing to try would be to use Aliases on your tables, this seems to help out the JET engine as well.
UPDATE Table3
INNER JOIN
(Table1 INNER JOIN Table2 ON Table1.uid = Table2.uid)
ON
(Table3.uid = Table2.uid)
AND
(Table3.uid = Table1.uid)
SET
Table2.field=NULL;
What I did is:
1. Created 3 tables
2. Establish relationships between them
3. And used the query builder to update a field in Table2.
There seems to be a problem in the query logic. In your first example, you LEFT JOIN to Table2 on Field1, but then have
Table2.Field1 IS NULL
in the WHERE clause. So, this limits you to records where no JOIN could be made. But then you try and update Table 1 with data from Table2, despite there being no JOIN.
Perhaps you could explain what it is you are trying to do with this query?
I need to search across multiple columns from two tables in my database using Full-Text Search. The two tables in question have the relevant columns full-text indexed.
The reason I'm opting for Full-text search:
1. To be able to search accented words easily (cafè)
2. To be able to rank according to word proximity, etc.
3. "Did you mean XXX?" functionality
Here is a dummy table structure, to illustrate the challenge:
Table Book
BookID
Name (Full-text indexed)
Notes (Full-text indexed)
Table Shelf
ShelfID
BookID
Table ShelfAuthor
AuthorID
ShelfID
Table Author
AuthorID
Name (Full-text indexed)
I need to search across Book Name, Book Notes and Author Name.
I know of two ways to accomplish this:
Using a Full-text Indexed View: This would have been my preferred method, but I can't do this because for a view to be full-text indexed, it needs to be schemabound, not have any outer joins, have a unique index. The view I will need to get my data does not satisfy these constraints (it contains many other joined tables I need to get data from).
Using joins in a stored procedure: The problem with this approach is that I need to have the results sorted by rank. If I am making multiple joins across the tables, SQL Server won't search across multiple fields by default. I can combine two individual CONTAINS queries on the two linked tables, but I don't know of a way to extract the combined rank from the two search queries. For example, if I search for 'Arthur', the results of both the Book query and the Author query should be taken into account and weighted accordingly.
Using FREETEXTTABLE, you just need to design some algorithm to calculate the merged rank on each joined table result. The example below skews the result towards hits from the book table.
SELECT b.Name, a.Name, bkt.[Rank] + akt.[Rank]/2 AS [Rank]
FROM Book b
INNER JOIN Author a ON b.AuthorID = a.AuthorID
INNER JOIN FREETEXTTABLE(Book, Name, #criteria) bkt ON b.ContentID = bkt.[Key]
LEFT JOIN FREETEXTTABLE(Author, Name, #criteria) akt ON a.AuthorID = akt.[Key]
ORDER BY [Rank] DESC
Note that I simplified your schema for this example.
I had the same problem as you but it actually involved 10 tables (a Users table and several others for information)
I did my first query using FREETEXT in the WHERE clause for each table but the query was taking far too long.
I then saw several replies about using FREETEXTTABLE instead and checking for not nulls values in the key column for each table, but that took also to long to execute.
I fixed it by using a combination of FREETEXTTABLE and UNION selects:
SELECT Users.* FROM Users INNER JOIN
(SELECT Users.UserId FROM Users INNER JOIN FREETEXTTABLE(Users, (column1, column2), #variableWithSearchTerm) UsersFT ON Users.UserId = UsersFT.key
UNION
SELECT Table1.UserId FROM Table1 INNER JOIN FREETEXTTABLE(Table1, TextColumn, #variableWithSearchTerm) Table1FT ON Table1.UserId = Table1FT.key
UNION
SELECT Table2.UserId FROM Table2 INNER JOIN FREETEXTTABLE(Table2, TextColumn, #variableWithSearchTerm) Table2FT ON Table2.UserId = Table2FT.key
... --same for all tables
) fts ON Users.UserId = fts.UserId
This proved to be incredibly much faster.
I hope it helps.
I don't think the accepted answer will solve the problem. If you try to find all the books from a certain author and, therefore, use the author's name (or part of it) as the search criteria, the only books returned by the query will be those which have the search criteria in its own name.
The only way I see around this problem is to replicate the Author's columns that you wish to search by in the Book table and index those columns (or column since it would probably be smart to store the author's relevant information in an XML column in the Book table).
FWIW, in a similar situation our DBA created DML triggers to maintain a dedicated full-text search table. It was not possible to use a materialized view because of its many restrictions.
I would use a stored procedure. The full text method or whatever returns a rank which you can sort by. I am not sure how they will be weighted against eachother, but I'm sure you could tinker for awhile and figure it out. For example:
Select SearchResults.key, SearchResults.rank From FREETEXTTABLE(myColumn, *, #searchString) as SearchResults Order By SearchResults.rank Desc
This answer is well overdue, but one way to do this if you cannot modify primary tables is to create a new table with the search parameters added to one column.
Then create a full text index on that column and query that column.
Example
SELECT
FT_TBL.[EANHotelID] AS HotelID,
ISNULL(FT_TBL.[Name],'-') AS HotelName,
ISNULL(FT_TBL.[Address1],'-') AS HotelAddress,
ISNULL(FT_TBL.[City],'-') AS HotelCity,
ISNULL(FT_TBL.[StateProvince],'-') AS HotelCountyState,
ISNULL(FT_TBL.[PostalCode],'-') AS HotelPostZipCode,
ISNULL(FT_TBL.[Latitude],0.00) AS HotelLatitude,
ISNULL(FT_TBL.[Longitude],0.00) AS HotelLongitude,
ISNULL(FT_TBL.[CheckInTime],'-') AS HotelCheckinTime,
ISNULL(FT_TBL.[CheckOutTime],'-') AS HotelCheckOutTime,
ISNULL(b.[CountryName],'-') AS HotelCountry,
ISNULL(c.PropertyDescription,'-') AS HotelDescription,
KEY_TBL.RANK
FROM [EAN].[dbo].[tblactivepropertylist] AS FT_TBL INNER JOIN
CONTAINSTABLE ([EAN].[dbo].[tblEanFullTextSearch], FullTextSearchColumn, #s)
AS KEY_TBL
ON FT_TBL.EANHotelID = KEY_TBL.[KEY]
INNER JOIN [EAN].[dbo].[tblCountrylist] b
ON FT_TBL.Country = b.CountryCode
INNER JOIN [EAN].[dbo].[tblPropertyDescriptionList] c
ON FT_TBL.[EANHotelID] = c.EANHotelID
In the code above [EAN].[dbo].[tblEanFullTextSearch], FullTextSearchColumn is the new table and column with the fields added, you can now do a query on the new table with joins to the table you want to display the data from.
Hope this helps