I've a question. I've this table structure here:
When I have now an issue in my table which has also different labels in my labels table and I want to delete the issue now, do I need to delete the labels before?
I'm planing to delete the entry this way:
DELETE FROM issues WHERE issue_id = 2;
The entries in my labels table are:
---------------------------------
| id | issue_id | label |
---------------------------------
| 1 | 2 | Apple |
---------------------------------
| 1 | 2 | Orange |
---------------------------------
| 1 | 2 | Banana |
---------------------------------
You should delete entries which reference your issue_id before you can delete it in the base table itself.
First you'll have to delete it from the labels table, then you can delete it from the issues table.
Related
I created a table (t_subject) like this
| id | description | enabled |
|----|-------------|---------|
| 1 | a | 1 |
| 2 | b | 1 |
| 3 | c | 1 |
And another table (t_place) like this
| id | description | enabled |
|----|-------------|---------|
| 1 | d | 1 |
| 2 | e | 1 |
| 3 | f | 1 |
Right now data from t_subject is used for each of t_place records, to show HTML dropdowns, with all the results from t_subject.
So I simply do
SELECT * FROM t_subject WHERE enabled = 1
Now just for one of t_place records, one record from t_subject should be hidden.
I don't want to simply delete it with javascript, since I want to be able to customize all of the dropdowns if anything changes.
So the first thing I though was to add a place_id column to t_subject.
But this means I have to duplicate all of t_subject records, I would have 3 of each, except one that would have 2.
Is there any way to avoid this??
I thought adding an id_exclusion column to t_subject so I could duplicate records only whenever a record is excluded from another id from t_place.
How bad would that be?? This way I would have no duplicates, so far.
Hope all of this makes sense.
While you only need to exclude one course, I would still recommend setting up a full 'place-course' association. You essentially have a many-to-many relationship, despite not explicitly linking your tables.
I would recommend an additional 'bridging' or 'associative entity' table to represent which courses are offered at which places. This new table would have two columns - one foreign key for the ID of t_subject, and one for the ID of t_place.
For example (t_place_course):
| place_id | course_id |
|----------|-----------|
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 3 | 1 |
| 3 | 3 |
As you can see in my example above, place 3 doesn't offer course 2.
From here, you can simply query all of the courses available for a place by querying the place_id:
SELECT * from t_place_course WHERE place_id = 3
The above will return both courses 1 and 3.
You can optionally use a JOIN to get the other information about the course or place, such as the description:
SELECT `t_course`.`description`
FROM `t_course`
INNER JOIN `t_place_course`
ON `t_course`.`id` = `t_place_course`.`course_id`
INNER JOIN `t_place`
ON `t_place`.`id` = `place_id`
I'm trying to figure out the best way to update one of two fields in a table. I have a personrelationship table and it links two people and I would like to have each person be able to set the relationship type on their end.
PersonRelationship Table
id int
user1_id int
user2_id int
user1_reltype /* boss, manager, etc */
user2_reltype
Depending on whether the current user is either user1_id or user2_id in the table, I need to update the user_reltype accordingly. So basically if current userid is in the user1_id field then update user1_reltype otherwise update the user2_reltype.
Since you want each user to be able to independently manage their half of the relationship, you can simplify your table structure
--------------------------------------
| initiator_id | reltype | target_id |
When a person with ID 5 (the 'initiator') marks person with ID 9 (the 'target') as a friend, the table will contain:
---------------------------------------
| initiator_id | reltype | target_id |
+--------------+----------+-----------+
| 5 | 'friend' | 9 |
If person 9 later initiates a 'boss' connection with person 5, the entry can be created without interfering with the row previously created by person 5:
--------------------------------------
| initiator_id | reltype | target_id |
+--------------+---------+_----------+
| 9 | 'boss' | 5 |
This approach will make your table easy to read and your queries easy to write.
Extra:
If you do not already have it, consider creating another table to track relationship types ('reltype'):
-----------------
| id | type |
+----+----------+
| 1 | 'friend' |
| 2 | 'boss' |
and replace the string reltype's in the relationship table with foreign keys.
---------------------------------------
| initiator_id | reltype | target_id |
+--------------+----------+-----------+
| 5 | 1 | 9 |
| 9 | 2 | 5 |
I want to trigger an Update on multiple sql tables without creating a loop.
Lets say I have 2 tables:
Table: User_Names
---------------
|Name | Clark |
|Gen | Male |
|id | 1 |
---------------
Table: User_Ages
---------------
|Age | 34|
|Gen | Male |
|id | 1 |
---------------
The id's are unique and refer to the same person.I want to update the columnGen in User_Names, my trigger should update it in the other Table. I also want this to happen when I change it in User_Ages Table, But if both update eachother im creating a loop on the Update trigger in mysql. How do I prevent this loop? The point here is creating a SQL Trigger.
I'm not going to address your original question given the nature of your example. This is a normalization issue much more than trigger issue.
In this case you should normalize your data and only store it in one place. Example above also suggests that you have slight misunderstanding on how to use rows and columns.
Given the example, better layout would probably be:
Table: User_names
+----+---------+------+
| id | Name | gen |
+----+---------+------+
| 1 | Clark | Male |
+----+---------+------+
Table: User_Ages
+----+------+
| id | age |
+----+------+
| 1 | 34 |
+----+------+
When you want to retrieve both values, you'd just link them in your query, e.g.
SELECT user_names.id,name,gen,age FROM User_names JOIN User_Ages USING (id);
Would give you:
+----+---------+------+-----+
| id | Name | gen | age |
+----+---------+------+-----+
| 1 | Clark | Male | 34 |
+----+---------+------+-----+
Coming back to your original question: In situation like that I'd question the original design. If it is really called for, then I'd pick one table that acts as a master and propagates the changes to other table. E.g. define the trigger on User_names table and use it to populate User_Ages table as well.
I'm building a website with a large number of categories, each with its own specific form fields. Because there are so many categories, I wanted to store those form fields in a database.
The categories are stored in a category table:
id | name
-------------
1 | Car info
The fields for that category are stored in a category_field table:
id | fk_id_category | type | label
-------------------------------------------------------------
1 | 1 | text | Your name
2 | 1 | radio | What type of car do your drive?
If a category_field has some predefined options from which the user can choose then these are stored in a category_field_option table:
id | fk_id_category_field | label
-----------------------------------------
1 | 2 | 'Convertible'
2 | 2 | 'Truck'
3 | 2 | 'Minivan'
Now, when a user fills out a form we want to save a reference to this in a form_entry table:
id | fk_id_user | fk_id_category
--------------------------------
1 | 1 | 1
The details of that form entry are saved in a form_entry_details table. However:
If the category_field.type is text we should just save the answer as string
id | fk_id_form_entry | fk_id_category_field | [answer]
-------------------------------------------------------
1 | 1 | 1 | John Doe
If the category_field.type is radio, I want to save a foreign key to the category_field_option
id | fk_id_form_entry | fk_id_category_field | [fk_id_category_field_option]
--------------------------------------------------------------------------
2 | 1 | 2 | 2
How can I solve this? I know I could just store the fk_id_category_field_option as a string, but I need it to actually reference to the category_field_option table since I'm using an ORM (Doctrine 1.2.4).
You can't because the whole idea of foreign keys is to prevent this sort of situation. You either store it as one field without an enforce foreign key or you create two columns, one for the foreign key id (perhaps a default value that relates to 'user defined') and another that takes the user defined info and, probably, defaults to null.
I have a table which only contains id and a field whose data is a list of data. e.g.
--------------
| id | data |
| 1 | a,b,c,d|
| 2 | a,b,k,m|
---------------
I guess it's not a good design that put a list data in a field, so I want to know how can I redesign it?
As per me you need two tables i.e. Master and Transaction tables only when some details are gonna be same for every records and some are gonna be changing. In your case if there are not any other thing related to your id field is gonna be same you can carry on with one table and with following structure.
--------------
| id | data |
| 1 | a |
| 1 | b |
| 1 | c |
| 1 | d |
| 2 | a |
| 2 | b |
| 2 | k |
| 2 | m |
---------------
BUT if there are any other things related to the id fields that is gonna be same for same id records you will have to use two tables.
like following case. there are 3 fields id, name and data.
and you current table looks something like
--------------------------
| id | name | data |
| 1 | testname | a,b,c,d|
| 2 | remy | a,b,c,d|
--------------------------
your new table structure should look like.
table 1 Master
-----------------
| id | name |
| 1 | testname |
| 2 | remy |
-----------------
Table 2 Transaction
--------------
| id | data |
| 1 | a |
| 1 | b |
| 1 | c |
| 1 | d |
| 2 | a |
| 2 | b |
| 2 | k |
| 2 | m |
---------------
For better database management we might need to normalize the data.
Database normalization is the process of organizing the fields and tables of a relational database to minimize redundancy and dependency. Normalization usually involves dividing large tables into smaller (and less redundant) tables and defining relationships between them. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships. You can find more on below links
3 Normal Forms Database Tutorial
Database normalization
If you have only those two fields in your table then you should have only 1 table as below
id | data
with composite primary key as PRIMARY KEY(id,data) so that there won't be any duplicate data for the respective ID.
The data would be like this
id | data
1 | a
1 | b
1 | c
1 | d
2 | a
2 | b
2 | k
2 | m
You will need another table which can be of the ONE to MANY type.
For e.g. you could have another table datamapping which would have data and ID column where the ID column is a FOREIGN KEY to the ID column of the data table.
So according to your example there would be 4 entries for ID = 1 in the datamapping table.
You will need two tables with a foreign key.
Table 1
id
Table 2
id
datavalue
So the data looks like:
Table 1:
id
1
2
3
Table 2:
id | data
1 | a
1 | b
1 | c
1 | d
2 | a
2 | b
2 | k
2 | m
You are correct, this this is not a good database design. The data field violates the principle of atomicity and therefore the 1NF, which can lead to problems in maintaining and querying the data.
To normalize your design, split the original table in two. There are 2 basic strategies to do it: using non-identifying and using identifying relationship.
NOTE: If you only have id in the parent table, and no other FKs on it, and parent cannot exist without at least one child (i.e. data could not have been empty in the original design), you can dispense with the parent table altogether.