I have say three tables.
Projects
Id
Name
Categories
Id
Name
ProjectCategories
Id
ProjectId
CategoryId
I now have an array of strings which represents categories the user has elected to search on. I now need to find all the projects that have those category attached to them.
I tried;
string[] searchTerms = new string[2];
searchTerms[0] = "paint";
searchTerms[1] = "painting";
IQueryable<Project> projects = (from category in dc.ProjectCategories
where searchTerms.Any(val => category.Category.Name.Contains(val))
select category.Project).Distinct();
But I get the error;
{"Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator."}
Unless I'm mistaking your meaning, which is possible, I think you can just do a contains with the searchTerms
where searchTerms.Contains( category.Category.Name )
this will translate into SQL as
... WHERE Name IN ('paint','painting') ...
Related
Let me start by saying that I am new to mysql and have searched on this site and others for a solution that will work for me. I've gotten fairly close (I think), but can't seem to find a solution.
I'm working on a Joomla site using RSForms software. I need to search a table where one row contains FirstName, another row contains LastName, and another row contains Email. Ultimately, I am looking for SubmissionId that is common to all 3. SubmissionId is a number generated by some form software that groups all of the form submission's elements by this id. I need to search for this id that is common to all 3. Each of the 3 elements may contain duplicates of the search. For instance, searching for the first name "John" will likely produce multiple results. I want to find the SubmissionId that matches "John" and last name "Doe" and email "johndoe#gmail.com" so I can use that to look up other information. It is also possible that there could be multiple matches for "John", "Doe", and johndoe#gmail.com".
I've tried many variations of the following (with/without ANY) and putting the results into an array and counting through each element. I've only had success in acquiring the first instance of "John".
$getresults = $db->setQuery("SELECT SubmissionId FROM my_table_values WHERE FormId = '$formid' AND FieldValue = '$fname' AND SubmissionId = ANY
(SELECT SubmissionId FROM my_table_values WHERE FormId = '$formid' AND FieldValue = '$lname' AND SubmissionId = ANY
(SELECT SubmissionId FROM my_table_values WHERE FormId = '$formid' AND FieldValue = '$email' ))");
---SubmissionValueId---|---FormId---|---SubmissionId---|---FieldName---|---FieldValue---
---------18192---------|-----20-----|-------5462-------|-----Email-----|---johndoe#gmail.com---
---------18193---------|-----20-----|-------5462-------|-----FName-----|---John---
---------18194---------|-----20-----|-------5462-------|-----LName-----|---Doe---
One possibility is to use a query that joins my_table_values with itself, even two times, to create something that can then be checked. For instance ... (fair warning: extemporaneous coding) ...
select A.submission_id from my_table_values A inner join my_table_values B using (SubmissionID) inner join my_table_values C using (SubmissionID) where (A.formID="email" and A.fieldValue= "foo#bar.com") and (B.formID="lastname" and B.fieldValue= "bar") and (C.formID="first name" and C.fieldValue="bletch")
You will need to examine that query to see (a) if the SQL processor accepts it, and (b) what sort of execution-plan it came up with. Preferably, all of the fields should be indexed. You need to see that it plans to use the indexes each time to narrow the list of possibilities, and that it plans to use the most-selective field (e.g. "email") first.
(The using (fieldname) syntax is specific to MySQL. You might need to use on to do the same thing.)
$getresults = $db->setQuery("
SELECT
MAX(IF(FieldValue = '$fname',SubmissionId, NULL) as fnameId,
MAX(IF(FieldValue = '$lname',SubmissionId, NULL) as lnameId,
MAX(IF(FieldValue = '$email',SubmissionId, NULL) as emailId
FROM my_table_values
WHERE FormId = '$formid'
GROUP BY FormId");
I have the following table strutucture and am accessing them by using MySQL Entity Framework:
Table Users
- Id
- Name
Table Subscriptions
- Id
- Id_User
- Id_Course
Table Courses
- Id
- Name
What I would like and am having a hard time to do so is building a link query for all users that returns a list with each entry containing:
User Id;
User name;
Concat string separated by comma with all courses for the user or 'no courses' string if none.
This list should be filtered by a part of users name.
I've started to build the code but can't finish it:
var Model db = new Model();
var list = from user in db.Users
join ???
where user.Name.Contains(filter.Trim())
select new { Name = user.Name, Id = user.Id, ???}
Can anyone help me please ?
You should use navigation properties (like User.Subscriptions) for this. Depending on how you created the model they may already be there, else you first should add them.
var query = from u in db.Users
where user.Name.Contains(filter) // trim the filter value first
select new
{
u.Name,
u.Id,
Courses = u.Subscriptions.Select(s => s.Course.Name)
};
var result = query.AsEnumerable()
.Select(q => new
{
q.Name,
q.Id
Courses = string.Join(", ", q.Courses)
};
The reason for doing this in two phases is that string.Join can't directly be used in an EF LINQ expression (can't be turned into SQL) so it must be done in memory (i.e. after an AsEnumerable).
But still it may be efficient to do a projection first (the first part), otherwise too much data may be fetched from the database.
I have a database representing something like a bookstore. There's a table containing the categories that books can be in. Some categories are defined simply using another table that contains the category-item relationships. But there are also some categories that can be defined programmatically -- a category for a specific author can be defined using a query (SELECT item_id FROM items WHERE author = "John Smith"). So my categories table has a "query" column; if it's not null, I use this to get the items in the category, otherwise I use the category_items table.
Currently, I have the application (PHP code) make this decision, but this means lots of separate queries when we iterate over all the categories. Is there some way to incorporate this dynamic SQL into a join? Something like:
SELECT c.category, IF(c.query IS NULL, count(i.items), count(EXECUTE c.query)
FROM categories c
LEFT OUTER JOIN category_items i
ON c.category = i.category
EXECUTE requires a prepared statement, but I need to prepare a different statement for each row. Also, EXECUTE can't be used in expressions, it's just a toplevel statement. Suggestions?
What happens when you want to list books by publisher? Country? Language? You'd have to throw them all into a single "category_items" table. How would you pick which dynamic query to execute? The query-within-a-query method is not going to work.
I think your concept of "category" is too broad, which is resulting in overly complicated SQL. I would replace "category" to represent only "genre" (for books). Genres are defined in their own table, and item_genres connects them to the items table. Books-by-author and books-by-genre should just be separate queries at the application level, rather than trying to do them both with the same (sort of) query at the database/SQL level. (If you have music as well as books, they probably shouldn't all be stored in a single "items" table because they're different concepts ... have different genres, author vs. artist, etc.)
I know this does not really solve your problem in the way you'd like, but I think you'll be happier not trying to do it that way.
Here's how I finally ended up solving this in the PHP client.
I decided to just keep the membership in the category_items table, and use the dynamic queries during submission to update this table.
This is the function in my script that's called to update an item's categories during submission or updating. It takes a list of user-selected categories (which can only be chosen from categories that don't have dynamic queries), and using this and the dynamic queries it figures out the difference between the categories that an item is currently in and the ones it should be in, and inserts/deletes as necessary to get them in sync. (Note that the actual table names in my DB are not the same as in my question, I was using somewhat generic terms.)
function update_item_categories($dbh, $id, $requested_cats) {
$data = mysql_check($dbh, mysqli_query($dbh, "select id, query from t_ld_categories where query is not null"), 'getting dynamic categories');
$clauses = array();
while ($row = mysqli_fetch_object($data))
$clauses[] = sprintf('select %d cat_id, (%d in (%s)) should_be_in',
$row->id, $id, $row->query);
if (!$requested_cats) $requested_cats[] = -1; // Dummy entry that never matches cat_id
$requested_cat_string = implode(', ', $requested_cats);
$clauses[] = "select c.id cat_id, (c.id in ($requested_cat_string)) should_be_in
from t_ld_categories c
where member_type = 'lessons' and query is null";
$subquery = implode("\nunion all\n", $clauses);
$query = "select c.cat_id cat_id, should_be_in, (member_id is not null) is_in
from ($subquery) c
left outer join t_ld_cat_members m
on c.cat_id = m.cat_id
and m.member_id = $id";
// printf("<pre>$query</pre>");
$data = mysql_check($dbh, mysqli_query($dbh, $query), 'getting current category membership');
$adds = array();
$deletes = array();
while ($row = mysqli_fetch_object($data)) {
if ($row->should_be_in && !$row->is_in) $adds[] = "({$row->cat_id}, $id)";
elseif (!$row->should_be_in && $row->is_in) $deletes[] = "(cat_id = {$row->cat_id} and member_id = $id)";
}
if ($deletes) {
$delete_string = implode(' or ', $deletes);
mysql_check($dbh, mysqli_query($dbh, "delete from t_ld_cat_members where $delete_string"), 'deleting old categories');
}
if ($adds) {
$add_string = implode(', ', $adds);
mysql_check($dbh, mysqli_query($dbh, "insert into t_ld_cat_members (cat_id, member_id) values $add_string"),
"adding new categories");
}
}
Good evening guys,
I'm a newbie to web programming and I need your help to solve a problem inherent to SQL query.
The database engine I'm using is MySQL and I access it via PHP, here I'll explain a simplified version of my database, just to fix ideas.
Let's suppose to work with a database containing three tables: teams, teams_information, attributes. More precisely:
1) teams is a table containing some basic information about italian football teams (soccer, not american football :D), it is formed by three fields: 'id' (int, primary key), 'name' (varchar, team name), nickname (Varchar, team nickname);
2) attributes is a table containing a list of possible information about a football team, such as city (the city where team plays its home match), captain (team captain's fullname), f_number (number of fans) and so on. This table is formed by three fields: id (int, primary key), attribute_name (varchar, an identifier for the attribute), attribute_desc (text, an explanation of the meaning of attribute). Each record of this table represents a single possible attribute of a football team;
3) teams_information is a table where some information, about teams listed in team table, are available. This table contains three fields: id (int, primary key), team_id (int, a foreign key which identifies a team), attribute_id (int, a foreign key which identifies one of the attributes listed in attributes table), attribute_value (varchar, the value of the attribute). Each record represents a single attribute of a single team. In general, different teams will have a different number of information, so for some teams a large number of attributes will be available while for other teams only a small number of attributes will be available.
Note that relation between teams and teams_information is one to many and the same relation exists between attributes and teams_information
Well, given this model my purpose is to realize a grid (maybe with ExtJS 4.1) to show user the list of italian football team, each record of this grid will represent a single football team and will contain all possible attributes: some fields may be empty (because, for considered team, the correspondent attribute is unknown), while the others will contain the values stored in teams_information table (for the considered team).
According to the above grid's field are: id, team_name and a number of fields to represent all the different attributes listed in 'attributes' table.
My question is: can I realize such a grid by using a SINGLE SQL query (maybe a proper SELECT query, to fetch all data I need from database tables) ?
Can anyone suggest me how to write a similar query (if it exists) ?
Thanks in advance for helping me.
Regards.
Enrico.
The short answer to your question is no, there is no simple construct in MySQL to achieve the result set you are looking for.
But it is possible to carefully (painstakingly) craft such a query. Here is an example, I trust you will be able to decipher it. Basically, I'm using correlated subqueries in the select list, for each attribute I want returned.
SELECT t.id
, t.name
, t.nickname
, ( SELECT v1.attribute_value
FROM team_information v1
JOIN attributes a1
ON a1.id = v1.attribute_id AND a1.attribute_name = 'city'
WHERE v1.team_id = t.id ORDER BY 1 LIMIT 1
) AS city
, ( SELECT v2.attribute_value
FROM team_information v2 JOIN attributes a2
ON a2.id = v2.attribute_id AND a2.attribute_name = 'captain'
WHERE v2.team_id = t.id ORDER BY 1 LIMIT 1
) AS captain
, ( SELECT v3.attribute_value
FROM team_information v3 JOIN attributes a3
ON a3.id = v3.attribute_id AND a3.attribute_name = 'f_number'
WHERE v3.team_id = t.id ORDER BY 1 LIMIT 1
) AS f_number
FROM teams t
ORDER BY t.id
For 'multi-valued' attributes, you'd have to pull each instance of the attribute separately. (Use the LIMIT to specify whether you are retrieving the first one, the second one, etc.)
, ( SELECT v4.attribute_value
FROM team_information v4 JOIN attributes a4
ON a4.id = v4.attribute_id AND a4.attribute_name = 'nickname'
WHERE v4.team_id = t.id ORDER BY 1 LIMIT 0,1
) AS nickname_1st
, ( SELECT v5.attribute_value
FROM team_information v5 JOIN attributes a5
ON a5.id = v5.attribute_id AND a5.attribute_name = 'nickname'
WHERE v5.team_id = t.id ORDER BY 1 LIMIT 1,1
) AS nickname_2nd
, ( SELECT v6.attribute_value
FROM team_information v6 JOIN attributes a6
ON a6.id = v6.attribute_id AND a6.attribute_name = 'nickname'
WHERE v6.team_id = t.id ORDER BY 1 LIMIT 2,1
) AS nickname_3rd
I use nickname as an example here, because American soccer clubs frequently have more than one nickname, e.g. Chicago Fire Soccer Club has nicknames: 'The Fire', 'La Máquina Roja', 'Men in Red', 'CF97', et al.)
NOT AN ANSWER TO YOUR QUESTION, BUT ...
Have I mentioned numerous times before, how much I dislike working with EAV database implementations? What should IMO be a very simple query turns into an overly complicated beast of a potentially light dimming query.
Wouldn't it be much simpler to create a table where each "attribute" is a separate column? Then queries to return reasonable result sets would look more reasonable...
SELECT id, name, nickname, city, captain, f_number, ... FROM team
But what really makes me shudder is the prospect that some developer is going to decide that the LDQ should be "hidden" in the database as a view, to enable the "simpler" query.
If you go this route, PLEASE PLEASE PLEASE resist any urge you may have to store this query in the database as a view.
I'm going to take a slightly different route. Spencer's answer is fantastic, and it addresses the issue quite well, but there's still a large underlying problem.
The data that you are trying to display on the site is over-normalized in the database. I won't elaborate, since, again, Spencer's answer highlights the issue pretty well.
Rather, I'd like to recommend a solution that denormalizes the data a bit.
Convert all of your Team data into a single table with many columns. (If there is Player data that isn't covered in the question, that would be a second table, but I'll gloss over that for now.)
Sure, you'll have a whole bunch of columns, and a lot of the columns might be NULL for a lot of the rows. It's not normalized, and it's not pretty, but here's the huge advantage that you gain.
Your query becomes:
SELECT * FROM Teams
That's it. That gets displayed right to the website and you are done. You might have to go out of your way to realize this schema, but it would be totally worth the time investment.
I think what you're saying is that you want the rows in the attributes table to appear as columns in the result recordset. If this is correct, then then in SQL you would use PIVOT.
A quick search on SO seems to indicate that there is no PIVOT equivalent in MySql.
I wrote a simple PHP script to generalize spencer's idea to solve my issue.
Here's the code:
<?php
require_once('includes/db.config.php'); //this file performs connection to mysql
/*
* Following function requires a table name ($table)
* and a number of service fields ($num). Given those parameters
* it returns the number of table fields (excluding service fields).
*/
function get_fields_number($table,$num,$conn)
{
$query = "SELECT * FROM $table";
$result = mysql_query($query,$conn);
return mysql_num_fields($result)-$num; //remember there are $num service fields
}
/*
* Following function requires a table name ($table) and an array
* containing a list of service fields names. Given those parameters,
* it returns the list of field names. That list is contained within an array and
* service fields are excluded.
*/
function get_fields_name($table,$service,$conn)
{
$query = "SELECT * FROM $table";
$result = mysql_query($query,$conn);
$name = array(); //Array to be returned
for ($i=0;$i<mysql_num_fields($result);$i++)
{
if(!in_array(mysql_field_name($result,$i),$service))
{
//currently selected field is not a service field
$name[] = mysql_field_name($result,$i);
}
}
return $name;
}
//Below $conn is db connection created in 'db.config.php'
$query = "SELECT `name` FROM `detail_arg` WHERE visibility = 0";
$res = mysql_query($query,$conn);
if($res===false)
{
$err_msg = mysql_real_escape_string(mysql_error($conn));
echo "{success:false,data:'".$err_msg."'}";
die();
}
$arg = array(); //list of argument names
while($row = mysql_fetch_assoc($res))
{
$arg[] = $row['name'];
}
//Following function writes the select subquery which is
//necessary to build a column containing a single attribute.
function make_subquery($attribute) //$attribute contains attribute name
{
$query = "";
$query.="(SELECT incident_detail.arg_value ";
$query.="FROM incident_detail ";
$query.="INNER JOIN detail_arg ";
$query.="ON incident_detail.arg_id = detail_arg.id AND detail_arg.name='".$attribute."' ";
$query.="WHERE incident.id = incident_detail.incident_id) ";
$query.="AS $attribute";
return $query;
}
/*
echo make_subquery("date"); //debug code
*/
$subquery = array(); //list of subqueries
for($i=0;$i<count($arg);$i++)
{
$subquery[] = make_subquery($arg[$i]);
}
$query = "SELECT "; //final query containing subqueries
$fields = get_fields_name("incident",array("id","visibility"),$conn);
//list of 'incident' table's fields
for($i=0;$i<count($fields);$i++)
{
$query.="incident.".$fields[$i].", ";
}
//insert the subqueries
$sub = implode($subquery,", ");
$query .= $sub;
$query.=" FROM incident ORDER BY incident.id";
echo $query;
?>
I am very frustrated from linq to sql when dealing with many to many relationship with the skip extension. It doesn't allow me to use joinned queries. Not sure it is the case for SQL server 2005 but I am currently using SQL Server 2000.
Now I consider to write a store procedure to fetch a table that is matched by two tables e.g. Album_Photo (Album->Album_Photo<-Photo) and Photo table and only want the Photos data so I match the Album's ID with Album_Photo and use that ID to match the photo. In the store procedure I am just fetch all the joinned data. After that in the linq to sql, I create a new Album object.
e.g.
var albums = (from r in result
where (modifier_id == r.ModifierID || user_id == r.UserID)
select new Album() {
Name = r.Name,
UserID = r.UserID,
ModifierID = r.ModifierID,
ID = r.ID,
DateCreated = r.DateCreated,
Description = r.Description,
Filename = r.Filename
}).AsQueryable();
I used the AsQueryable to get the result as a IQueryable rather than IEnumerable. Later I want to do something with the collection, it gives me this error:
System.InvalidOperationException: The query results cannot be enumerated more than once.
It sounds like you have a situation where the query has already executed by the time you are want to filter it later in your code.
Can you do something like...
var albums = (blah blah blah).AsQueryable().Where(filterClause) when you have enough info to process
what happens if you try albums.where(filter) later on in the code? Is this what you are trying?