I have to join multiple tables, some with one to many mappings, and convert every entry in the joined table to a single row entry in a csv file using PHP.
I know I am basically going from a 3D to 2D representation, but it is a formatting requirement for the csv file.
The MySQL structure consists of tables "questions", "people" and "trips". "people" table is linked to "questions" table by the id of "questions". Also in the same way "trips" is linked to "people" by the id of "people". There are one to many relationship between both "questions" to "people" and "people" to "trips"
The idea is to have a csv file with one "question" entry per row. This row entry will be the joined result of all 3 tables. The number of people and trips per questions entry is not consistent, therefore spaces are required if there are fewer people in some "questions" entries than other. The same with the trips.
What is the best way to get this done in PHP, except for brute force coding this with many queries, for loops etc. I am trying to get the MySQL query going, but cannot wrap my head around this problem.
I think you're looking for mysql GROUP_CONCAT function.
Select data with joins, group it by question_id and use group_concat on people and trips columns.
Related
I have a question about a database design in MySQL.
There are two groups of people i have a separate table for. Call them TABLE student and TABLE professor.
I can give each of them assignments from TABLE assignments.
Each person in each group can have multiple assignments, and each assignment can have multiple people. So to keep track of these, I have two mapping tables, call them TABLE student_assignment and TABLE professor_assignment.
My question comes here. I have a single table TABLE assignment_results that I want to store the results from all the assignments in. I would like for each line of each mapping table to have a single record...so it seems to make more sense to have a separate results table for each group of people??? TABLE prof_assign_results and TABLE stud_assign_results
Or would it make sense to combine the mapping tables and avoid splitting altogether? Is it possible to define a unique index containing three columns? Would the NULL values (in either the student or professor columns) interfere with that?
I'm building a database for characters that would be analogous to DnD character sheets. There are a lot of fields for any one particular character. Like 100+.
Would it be more efficient to have one table with all the columns then save/load what I need, or separate out the columns into tables by category (like stats, equipment, skills, etc), then just join the one-to-one tables whenever I need certain info?
TDLR: Better to have 1 table with 100+ columns, or like 10 tables each with 10-20 columns?
I have a model titles
My titles DB table is getting rather large 100,000+ rows of data.
What is the best way to create a new titles2 table and join it with the titles table so that they can both be the same titles model?
Also if I finish adding rows to titles at id 100,000 should i start incrementing titles2 at id 100,001 to that the ids will always be unique?
You can add another column ex. source to differentiate these two table records. This way you can make sure that there's no way we will run into the problem of mixing these two datasets.
However for conveniency, we still want to make sure the id itself is unique across different dataset, which requires you not to use auto-increment for id field, because you'll gonna be the one to handle the id generation.
Some of the issues that I run into includes using the following line to update or insert the record,
$db->table('users')->insert($record);
instead of
User::create($record); // assume you are using auto-increment ids
I have to create a system to save user's vote for two different type of module: News and Video.
This table should have the same fields:
id
entry_id
vote
user_id
So I tought to add a new field to save also the name of the module (module), in this way I can have just one table in the DB and filter it when needed and create two views for statistic purpose.
I don't really know if the best solution is one table with the new field or is better have two different table.
Let's assume that I have 1000 news and 1000 users and all of them will vote each news I will have 1000000 rows in the table.
Now assume that I have also 1000 videos and also in this case all my users will vote it, other 1000000 rows for an amount of 2000000 rows in a single table.
Do I have any performance problem in this case? And If I will have much more video, news an users?
Operation that I should do:
Insert
Update
Search
If you need more infos please ask
I think the way to answer this question is based on entry_id. The votes are going to be about something and that something is going to reference another table.
So, if you have two separate tables for News and Videos, then you should have two separate votes tables. Neither will have entry_id. One will have news_id and the other video_id.
If you have one table, say Entries for both News and Videos, then have one table.
In other words, I am advising against having one table conditionally reference multiple other tables. It becomes very difficult to express foreign key restraints, for one thing. In addition, join operations are cumbersome to express. Someone else might visit the table and not realize that entry_id can refer to multiple tables, and incorrectly set up queries.
All of these problem can be overcome (and there are situations where one table may be the preferred solution). However, if the original entities are in different tables, then put the votes in different tables.
So I have 2 tables in my database, they are 'workouts' and 'exercises'. Workouts contains a row called exercises which is a comma-separated list of exercise IDs - from the 'exercises' table e.g. '1,2,3'.
My question is, can I write a single query to allow me to select a row from the workouts table, say one with an id of 1, and have MySQL fetch each of the exercises from the list in that row, returning them within the 'workout' row?
At the moment I'm using PHP to select the workout row, and then making individual requests for each of the exercises, resulting in serious inefficiency.
I took a look at Joining rows as array from another table for each row and also did some research into the group_concat() function, but I'm not sure that's what I'm after.
Update
Here are the 2 tables:
IMO, the best approach is to redesign your schema to have a cross-reference table called exercises_workouts (or something similar). Remove the CSV field.
Here's page that goes into more detail on implementing a many-to-many relationship:
http://www.tonymarston.net/php-mysql/many-to-many.html
Note: The linked page uses the mysql_* functions, but the general explanation of the approach stands. You'll want to look into PDO for database access.