I'm trying to create a separate table that would track read/unread posts. Using MySQLi I will have two tables items and items_tracking. When the page is rendered it will join the the tables and check if the user read the posts or not.
items
+-------+------------+----+
| id | created_by | .. |
+-------+------------+----+
| item1 | id12 | .. |
| item2 | id433 | .. |
+-------+------------+----+
items_tracking
+---------+---------+------+
| user_id | item_id | read |
+---------+---------+------+
| id1 | item1 | 0 |
| id2 | item2 | 0 |
| id94 | item1 | 1 |
+---------+---------+------+
Now the idea was that whenever a new item/post is created in the items table, it will also create rows in the items_tracking table for all users and with column read = 0. Problem is, I have no idea how to work around this since the foreign key I would use in items_tracking is still pretty much undetermined.
Any ideas on how to approach inserting in both tables at the same time, while the second table references the first?
You don't need records with read=0 in the tracking table.
SELECT ..., t.read FROM items i LEFT JOIN items_tracking t ON (t.item_id = i.id)
This query will work even if there is no corresponding record in items_tracking; in this case, t.read in the result will be NULL. You only need to insert the records with read = 1, although you don't need even this flag, you test for t.item_id IS NOT NULL to see if you have a record in items_tracking.
Related
I have two tables. The first one (item) is listing apartments. The second (feature) is a list of features that an apartment could have. Currently we list about 25 different features.
As every apartment can have a different set of features, I think it makes sense to have a 1:1 relationship between items and features table.
If in feature table for one the features the value is '1', this means that the linked apartment has this feature.
+-------------+------------+--------------+-------------+------------+
| table: item | | | | |
+-------------+------------+--------------+-------------+------------+
| id | created_by | titel | description | address |
+-------------+------------+--------------+-------------+------------+
| 10 | user.id | Nice Flat | text | address.id |
+-------------+------------+--------------+-------------+------------+
| 20 | user.id | Another Flat | text | address.id |
+-------------+------------+--------------+-------------+------------+
| 30 | user.id | Bungalow | text | address.id |
+-------------+------------+--------------+-------------+------------+
| 40 | user.id | Apartment | text | address.id |
+-------------+------------+--------------+-------------+------------+
+----------------+---------+--------------+----------------+--------------+------+
| table: feature | | | | | |
+----------------+---------+--------------+----------------+--------------+------+
| id | item_id | key_provided | security_alarm | water_supply | lift |
+----------------+---------+--------------+----------------+--------------+------+
| 1 | 10 | 1 | 0 | 0 | 1 |
+----------------+---------+--------------+----------------+--------------+------+
| 2 | 20 | 0 | 1 | 1 | 0 |
+----------------+---------+--------------+----------------+--------------+------+
| 3 | 30 | 1 | 1 | 0 | 1 |
+----------------+---------+--------------+----------------+--------------+------+
| 4 | 40 | 1 | 1 | 1 | 1 |
+----------------+---------+--------------+----------------+--------------+------+
I want to build a filter functionality so user can select to show only apartments with certain features.
e.g.:
$key_provided = 1;
$security_alarm = 1;
$water_supply = 0;
Does this database approach sounds reasonable for you?
What’s the best way to build a MySQL query to retrieve only apartments where the filter criteria match, keeping in mind that the number of features can be grow in future?
A better approach is to have a features table. In your case, they all seem to be binary -- yes or no -- so you can get away with:
create table item_features (
item_feature_id int auto_increment primary key,
item_id int not null,
feature varchar(255)
foreign key item_id references items(item_id)
);
The data would then have the positive features, so the first item would be:
insert into item_features (item_id, feature)
values (1, 'key_provided'), (1, 'lift');
This makes it easy to manage the features, particularly adding new ones. You might want to use a trigger, check constraint, or reference table to validate the feature names themselves, but I don't want to stray too far from your question.
Then checking for features is a little more complicated, but not that much more so. One method is explicitly using exists and not exists for each desired/undesired one:
select i.*
from items i
where exists (select 1
from item_features itf
where itf.item_id = i.item_id and
itf.feature = 'key_provided'
) and
exists (select 1
from item_features itf
where itf.item_id = i.item_id and
itf.feature = 'security_alarm'
) and
not exists (select 1
from item_features itf
where itf.item_id = i.item_id and
itf.feature = 'water supply'
);
For your existing data structure, you can filter as follows:
select i.*
from item i
inner join feature f
on f.item_id = i.id
and f.key_provided = 1
and f.security_alarm = 1
and f.water_supply = 0
This will give you all the apartments that satisfy the given criteria. For more criterias, you can just add more conditions to the on part of the join.
As a general comment about your design:
since you are creating a 1-1 relationship between apartments and features, you might as well consider having a single table to store them (spreading the information over two tables does not have any obvious advantages)
your design is OK as long as features do not change too often, since, basically, everytime a new feature is created, you need to add more columns to your table. If features are added (or removed) frequently, this can become heavy to manage; in that case, you could consider having a separated table where each (item, feature) tuple is stored in a different row, which will make this of things easier to do (with the downside that queries will get more complicated to write)
I have a table products and a table locations which are linked together in a many-to-many relationship with a table products_locations. Now a client can select a set of products, and I want to run a query that selects only the locations, where ALL of the selected products are available.
This seemed pretty straight forward at first, but I see myself being quite baffled by how to achieve this. I initially thought I could get all the correct location-ids with something like
SELECT location_id
FROM products_locations
WHERE product_id = ALL [the user selected product ids]
But on second thought that does not appear to make sense either (the structure of products_locations is quite simply [product_id, location_id].
Any suggestion on how to structure such a query would be appreciated. I feel like I am overlooking something basic..
EDIT: I am using mysql syntax/dialect
Quick sample: Given the following tables
| products | | locations | | products_locations |
| id | name | | id | name | | product_id | location_id |
|------------| |-----------| |--------------------------|
| 1 | prod1 | | 1 | locA | | 1 | 2 |
| 2 | prod2 | | 2 | locB | | 2 | 1 |
| 3 | prod3 | |-----------| | 2 | 2 |
|------------| | 3 | 1 |
|--------------------------|
If a user selects products 1 and 2, the query should return only location 2. If the user selects products 2 and 3, the query should return location 1. For 1, 2, and 3, no location would be valid, and for product 2, both locations would be valid.
I figured out a query that achieves what I need. Though it is not as clean as I had hoped, it seems to be a robust approach to what I'm trying to query:
SELECT t.location_id
FROM (SELECT location_id, COUNT(*) as n_hits
FROM products_locations
WHERE product_id IN [the user selected products]
GROUP BY location_id) t
WHERE n_hits = [the number of user selected products];
Explanation:
I create a temporary table t which contains every location_id that has at least one matching product in the user's selection, together with the number of times that location matches a product in the user's selection. This is achieved by grouping the query by location_id.
I select the location_id(s) from that temporary table t, where the number of hits is equal to the number of products the user had selected. If that number is lower, I know that at least one product did not match that location.
I am moving an old Mantis table that had a varchar(64) category_id column to a new Mantis table that has a int(10) category_id column.
The simplified structure is as follows
bug_table (Old DB)
+----+-------------+-------------+--------+
| id | project_id | category_id | report |
+----+-------------+-------------+--------+
| 1 | 0 | Server | crash |
| 2 | 0 | Database | error |
| 3 | 1 | Server | bug |
| 4 | 1 | Server | crash |
+----+-------------+-------------+--------+
category_table (New DB)
+----+------------+----------+
| id | project_id | name |
+----+------------+----------+
| 0 | 1 | Server |
| 1 | 1 | Database |
| 2 | 2 | Server |
| 3 | 2 | Database |
+----+------------+----------+
I need a magical query that will replace category_id in the bug_table with the numerical category_id in the category_table. Thankfully I am able to match rows by project_id and categories by name.
Here is the query I am working on but have gotten stuck in the complexity
UPDATE bug_table b SET b.category_id = c.id USING category_table WHERE b.category_id = c.name
I like to approach such a task a little differently than you do for a new lookup/reference table.
To me, the new category table would only have id and name columns. There are only two rows based on the sample data: Server and Database. Yes, I realize there could be other names, but those can easily be added, and should be added, before proceeding to maximize the id matching that follows.
Next I would add a new column to the bug table that could be called 'category_new' with the data type that will store the new category id. Alternatively, you could rename the existing category_id column to category, and the new column for the id's could then be column_id.
After all that is done then you can update the new column by joining the category on names and set the id that matches: (note this assumes the non-alternative approach mentioned in step 2)
UPDATE bug_table JOIN category_table ON bug_table.category_id = category_table.name
SET bug_table.category_new = category_table.id
After that runs, check the new column to verify the updated id's.
Finally, after successful update, now the old category_id column (with the names) from the bugs_table can be dropped, and the category_new column can be renamed as the category_id.
=====
Note that if you decide to go with the alternative column approach mentioned, of course the query will be similar but differ slightly. Then only a column drop is needed at the end
If there are other tables to apply the same category changes, the operation (basically steps 2 through 5) would be similar for those tables too.
I'M trying to extract all information into my table, but I need to change id, when available, to the name into another table.
I have 1 table like that:
|------------------------------|
|-id-|-systems-|-remote-|-deco-|
| 1 | NULL | 3 | |
| 2 | 21 | NULL | 2 |
|-------------------------------
each column like "systems" / "remote" / "deco" refer to an id into another table
I know how to use INNER JOIN. But if I use that, I got an empty result because the value need to be appears into the others tables.
ex.:
SELECT qd.id,s.name as systems,r.name as remote, d.name as deco
FROM `quote_data` qd
INNER JOIN systems s ON qd.systems=s.id
INNER JOIN remote r ON qd.remote=r.id
INNER JOIN deco d ON qd.deco=d.id
I got empty result.
In the best words, I need to do something like:
|------------------------------|
|-id-|-systems-|-remote-|-deco-|
| 1 | | R42 | |
| 2 | GTV | | B21 |
|-------------------------------
Also, I use innoDB table
Any Idea how to fix that?
I have two tables
one as td_job which has these structure
|---------|-----------|---------------|----------------|
| job_id | job_title | job_skill | job_desc |
|------------------------------------------------------|
| 1 | Job 1 | 1,2 | |
|------------------------------------------------------|
| 2 | Job 2 | 1,3 | |
|------------------------------------------------------|
The other Table is td_skill which is this one
|---------|-----------|--------------|
|skill_id |skill_title| skill_slug |
|---------------------|--------------|
| 1 | PHP | 1-PHP |
|---------------------|--------------|
| 2 | JQuery | 2-JQuery |
|---------------------|--------------|
now the job_skill in td_job is actualy the list of skill_id from td_skill
that means the job_id 1 has two skills associated with it, skill_id 1 and skill_id 2
Now I am writing a query which is this one
SELECT * FROM td_job,td_skill
WHERE td_skill.skill_id IN (SELECT td_job.job_skill FROM td_job)
AND td_skill.skill_slug LIKE '%$job_param%'
Now when the $job_param is PHP it returns one row, but if $job_param is JQuery it returns empty row.
I want to know where is the error.
The error is that you are storing a list of id's in a column rather than in an association/junction table. You should have another table, JobSkills with one row per job/skill combination.
The second and third problems are that you don't seem to understand how joins work nor how in with a subquery works. In any case, the query that you seem to want is more like:
SELECT *
FROM td_job j join
td_skill s
on find_in_set(s.skill_id, j.job_skill) > 0 and
s.skill_slug LIKE '%$job_param%';
Very bad database design. You should fix that if you can.