Retrieve the row based on the user_id and also include any rows that have the same event_id as that entry

Question

Retrieve the row based on the user_id and also include any rows that have the same event_id as that entry

I have a table with the following structure:

 _______________________________
| event_id | user_id | username |
|-------------------------------|
|    30    |    1    |   user1  |
|    30    |    2    |   user2  |
|    30    |    3    |   user3  |
|    31    |    1    |   user1  |
|    31    |    4    |   user4  |
|    31    |    7    |   user5  |
|    32    |    3    |   user1  |
|    32    |    4    |   user4  |
|    32    |    5    |   user5  |
|_______________________________|

I initially thought about storing users as JSON:

 _______________________________________________________
| event_id |                   users                    |
|-------------------------------------------------------|
|    30    | [{"user_id": 1, "username": "user1"}, ...] |
|    31    | [{"user_id": 1, "username": "user1"}, ...] |
|    32    | [{"user_id": 5, "username": "user5"}, ...] |
|_______________________________________________________|

However, I anticipate that this approach would negatively impact performance when attempting to search for an event based on a specific JSON value.

I am looking for a way to query and retrieve all events where a username is present, returning all rows with matching event_id. Is it possible to accomplish this using a single query in order to minimize server load, or would it be better to use a nested select statement?

mysql sql node.js json

Answer 1

Answer №1

I need the ability to search for occurrences of a specific username within events and retrieve all rows that share the same event_id.

A possible solution is to utilize the "exists" clause along with a correlated subquery:

SELECT t.*
FROM mytable t
WHERE EXISTS (
    SELECT 1 FROM mytable t1 WHERE t1.event_id = t.event_id AND t1.username = ?
)

To enhance performance, it would be beneficial to create an index on the columns (username, event_id).

The question mark denotes the placeholder for the targeted username.

Personally, I would advise against storing data as JSON in this scenario since it would add unnecessary complexity to queries without providing significant benefits. The current tabular structure effectively accommodates the consistent nature of your stored information.

Answer 2

I need the ability to search for occurrences of a specific username within events and retrieve all rows that share the same event_id.

A possible solution is to utilize the "exists" clause along with a correlated subquery:

SELECT t.*
FROM mytable t
WHERE EXISTS (
    SELECT 1 FROM mytable t1 WHERE t1.event_id = t.event_id AND t1.username = ?
)

To enhance performance, it would be beneficial to create an index on the columns (username, event_id).

The question mark denotes the placeholder for the targeted username.

Personally, I would advise against storing data as JSON in this scenario since it would add unnecessary complexity to queries without providing significant benefits. The current tabular structure effectively accommodates the consistent nature of your stored information.

Answer 3

Answer №2

Discover the power of group_concat with this amazing query. You can see it in action on our interactive db-fiddle.

select
    event_id,
    concat('[', group_concat(concat('{"user_id":', user_id, ', "username":"',username,'"}')), ']') as users   
from yourTable
group by
    event_id

The above query will produce the following output:

| event_id | users                                                                                                       |
| -------- | ----------------------------------------------------------------------------------------------------------- |
| 30       | [{"user_id":1, "username":"user1"},{"user_id":2, "username":"user2"},{"user_id":3, "username":"user3"}] |
| 31       | [{"user_id":1, "username":"user1"},{"user_id":4, "username":"user4"},{"user_id":7, "username":"user5"}] |
| 32       | [{"user_id":3, "username":"user1"},{"user_id":4, "username":"user4"},{"user_id":5, "username":"user5"}] |

Answer 4

Discover the power of group_concat with this amazing query. You can see it in action on our interactive db-fiddle.

select
    event_id,
    concat('[', group_concat(concat('{"user_id":', user_id, ', "username":"',username,'"}')), ']') as users   
from yourTable
group by
    event_id

The above query will produce the following output:

| event_id | users                                                                                                       |
| -------- | ----------------------------------------------------------------------------------------------------------- |
| 30       | [{"user_id":1, "username":"user1"},{"user_id":2, "username":"user2"},{"user_id":3, "username":"user3"}] |
| 31       | [{"user_id":1, "username":"user1"},{"user_id":4, "username":"user4"},{"user_id":7, "username":"user5"}] |
| 32       | [{"user_id":3, "username":"user1"},{"user_id":4, "username":"user4"},{"user_id":5, "username":"user5"}] |

Answer 5

Answer №3

Based on your statement that a query is utilized to generate the table, here is a possible solution:

To obtain the desired outcome, you can execute the following SQL statement:

SELECT e.*, u.user_name
FROM events AS e 
JOIN users AS u
ON e.user_id = u.user_id
WHERE EXISTS (
    SELECT 1
    FROM events AS e2
    WHERE e2.event_id = e.event_id AND
    e2.user_id = :user_id -- choose the appropriate value for user_id
);

If this aligns with your query, it would be beneficial to create an index on events(event_id, user_id) in order to enhance performance.

Answer 6

Based on your statement that a query is utilized to generate the table, here is a possible solution:

To obtain the desired outcome, you can execute the following SQL statement:

SELECT e.*, u.user_name
FROM events AS e 
JOIN users AS u
ON e.user_id = u.user_id
WHERE EXISTS (
    SELECT 1
    FROM events AS e2
    WHERE e2.event_id = e.event_id AND
    e2.user_id = :user_id -- choose the appropriate value for user_id
);

If this aligns with your query, it would be beneficial to create an index on events(event_id, user_id) in order to enhance performance.

Answer 7

Answer №4

After careful consideration, I opted for a nested select query that retrieves the event_id. Initially, I disregarded this approach under the assumption that enabling the multiple statement queries option of node-mysql was necessary. However, it became apparent that this was not the case.

Answer 8

After careful consideration, I opted for a nested select query that retrieves the event_id. Initially, I disregarded this approach under the assumption that enabling the multiple statement queries option of node-mysql was necessary. However, it became apparent that this was not the case.

Retrieve the row based on the user_id and also include any rows that have the same event_id as that entry

Answer №1

Answer №2

Answer №3

Answer №4

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