I'm relatively new to MySql.
I have 2 tabled with the following structure
products
{
pid-autoincrement,
pname
p_desc
}
services
{
sid-autoincrement
s_name
s_desc
}
Im trying to select the products or services which have the name '%<somekeyword>%'
I'm using the query:
SELECT DISTINCT products.*,
services.*
FROM products, services
WHERE products.pname
LIKE '%mob%'
OR services.s_name
LIKE '%mob%'
But I'm getting a lot of repeated results.
Tried using joins but couldn't get a solution.
Can someone help me with this?
You want to use UNION, like this:
SELECT DISTINCT products.pid-autoincrement AS id,
products.pname AS name,
products.p_desc AS desc
FROM products
WHERE products.pname
LIKE '%mob%'
UNION
SELECT DISTINCT services.sid-autoincrement AS id,
services.s_name AS name,
services.s_desc AS desc
FROM services
WHERE services.s_name
LIKE '%mob%'
you have to use the UNION operator
therefore you can only select the same columns (as there is only one result)
or you select 2 times - 2 results
Because the tables aren't related you'll have to use the UNION operator (as karlis says), rather than JOIN. But as you apparently want to handle products and services together (at least some of the time) you're probably better off putting them into one table and adding a column to differentiate between them, like so:
productsandservice [need better name]
{
id,
name,
desc,
isaservice
}
Related
I am trying to query my PostgreSQL database to get the latest (by created_at) and distinct (by user_id) Activity objects, where each user has multiple activities in the database. The activity object is structured as such:
Activity(id, user_id, created_at, ...)
I first tried to get the below query to work:
Activity.order('created_at DESC').select('DISTINCT ON (activities.user_id) activities.*')
however, kept getting the below error:
ActiveRecord::StatementInvalid: PG::InvalidColumnReference: ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY expressions
According to this post: PG::Error: SELECT DISTINCT, ORDER BY expressions must appear in select list, it looks like The ORDER BY clause can only be applied after the DISTINCT has been applied. This does not help me, as I want to get the distinct activities by user_id, but also want the activities to be the most recently created activities. Thus, I need the activities to be sorted before getting the distinct activities.
I have come up with a solution that works, but first grouping the activities by user id, and then ordering the activities within the groups by created_at. However, this takes two queries to do.
I was wondering if what I want is possible in just one query?
This should work, try the following
Solution 1
Activity.select('DISTINCT ON (activities.user_id) activities.*').order('created_at DESC')
Solution 2
If not work Solution 1 then this is helpful if you create a scope for this
activity model
scope :latest, -> {
select("distinct on(user_id) activities.user_id,
activities.*").
order("user_id, created_at desc")
}
Now you can call this anywhere like below
Activity.latest
Hope it helps
There are 2 tables : User and Teacher. Teacher.user_id is from User. So, how do I find in a single query, all the users who are not in teachers.
I meant something along the lines :
User.not_in(Teacher.all)
You can use where.not query from ActiveRecord try something like below:
User.where.not(id: Teacher.pluck(:user_id).reject {|x| x.nil?})
Note: used reject method, in case you have nil values in some records.
The other users seem to have neglected the rails 3 tag (since removed based on the approved answer. My answer left for posterity) : Please try this
User.where("id NOT IN (?)",Teacher.pluck(:user_id).join(","))
This will become SELECT * FROM users WHERE id NOT IN (....) (two queries one to get the user_id from teachers and another to get the user(s) not in that list) and may fail based on the size of teacher table.
Other option is an arel table:
users = User.arel_table
User.where(users[:id].not_in(Teacher.select(:user_id).where("user_id IS NOT NULL")))
This should produce a single query similar to
SELECT * FROM users
WHERE id NOT IN ( SELECT user_id FROM teachers WHERE user_id IS NOT NULL)
(one query better performance) * syntax was not fully tested
Another single query option might be
User.joins("LEFT OUTER JOIN teachers ON teachers.user_id = users.id").
where("teachers.user_id IS NULL")
I think you should be able to do something like this
User.where.not(id: Teacher.ids)
I have two tables,
Order (ID, Value)
and
OrderType (ID, Name [Quote, Sale, Purchase, etc])
I want to get the total number of orders in each type (count) and the total value of those orders per type (sum)
I can get these individually using
Order.group(:order_type).count(:id)
and
Order.group(:order_type).sum(:value)
I would like to perform these in one query, the equivalent to the following SQL
SELECT
order_types.id, Count(*) as total_count, Sum(orders.value) As total_value
FROM
order
JOIN
order_types ON orders.order_type_id = order_types.ID
GROUP BY
order_types.id
The query should also return the full OrderType object so I can display the name in my view
Since ActiveRecord does not support multiple aggregation functions in the same query, you need to do a bit of raw SQL to achieve this.
grouped_sales = OrderType
.select('order_types.id, order_types.name,
sum(orders.value) as sale, count(*) as purchase')
.join('JOIN orders ON orders.order_type_id = order_types.id')
.group('order_types.id')
The point to note here is that you need to use an existing column in OrderType as the alias for your aggregated columns. Here you will get the OrderType object as well.
To access the result:
id -> grouped_sales.first.id
name -> grouped_sales.first.name
total orders -> grouped_sales.first.sale
order value -> grouped_sales.first.purchase
There is even better solution, just:
.pluck('sum(orders.value), count(*)').first
Nowadays pluck+arel will do the job.
model = Model.arel_table
Model.group(:order_type).pluck(model[:id].count, model[:value].sum)
Also appending with .order(:order_type) may be needed if there applied default ordering by ID.
What I want to do is to join table and sum 3 columns.
self.document_products.joins("JOIN products ON products.id = document_products.product_id").group("products.tax_id").select("sum(a), sum(b), sum(c)")
Gives me
#<ActiveRecord::Relation [#<DocumentProduct id: nil>]>
Something like that works:
self.document_products.joins("JOIN products ON products.id = document_products.product_id").group("products.tax_id").sum("a")
But I want to have 3 sums. I can`t do sum("a, b, c"). Where is the problem?
So, the code is building a SQL query using the ActiveRecord chained method syntax. It's possible to use .to_sql as the final part of most such chains (basically, as long as it's still an ActiveRecord object, rather than having been converted to an Array, for example) to see the SQL generated, or indeed inspecting the log, if it's on. Considering the common part of the chain:
self.document_products.joins("JOIN products ON products.id = document_products.product_id").group("products.tax_id")
This generates something like (might not be exact, because I'm guessing a little about your application):
SELECT "document_products".* FROM "document_products" JOIN products ON products.id = document_products.product_id WHERE "document_products"."document_id" = 1497 GROUP BY products.tax_id
The two final methods you list are very different; select selects which columns in the query to return, whereas sum is an aggregate function which expects a single value to be returned in each case. Considering the select, we get something like the following generated:
SELECT SUM(products.a), SUM(products.b), SUM(products.c) FROM "document_products" JOIN products ON products.id = document_products.product_id WHERE "document_products"."document_id" = 1497 GROUP BY products.tax_id
When this query is interpreted, the expected data cannot be found, leading to the problem described. Ensuring that the GROUP BY clause is included in the SELECT part, however, yields the necessary information. Try something like this:
self.document_products.joins("JOIN products ON products.id = document_products.product_id").group("products.tax_id").select("products.tax_id, sum(a), sum(b), sum(c)")
This generates SQL something like:
SELECT products.tax_id, SUM(products.a), SUM(products.b), SUM(products.c) FROM "document_products" JOIN products ON products.id = document_products.product_id WHERE "document_products"."document_id" = 1497 GROUP BY products.tax_id
This appears to return the necessary information, and is, I think, what you're looking for (or close to it).
I have a relationship between two models, Registers and Competitions. I have a very complicated dynamic query that is being built and if the conditions are right I need to limit Registration records to only those where it's Competition parent meets a certain criteria. In order to do this without select from the Competition table I was thinking of something along the lines of...
Register.where("competition_id in ?", Competition.where("...").collect {|i| i.id})
Which produces this SQL:
SELECT "registers".* FROM "registers" WHERE (competition_id in 1,2,3,4...)
I don't think PostgreSQL liked the fact that the in parameters aren't surrounded by parenthesis. How can I compare the Register foreign key to a list of competition ids?
you can make it a bit shorter and skip the collect (this worked for me in 3.2.3).
Register.where(competition_id: Competition.where("..."))
this will result in the following sql:
SELECT "registers".* FROM "registers" WHERE "registers"."competition_id" IN (SELECT "competitions"."id" FROM "competitions" WHERE "...")
Try this instead:
competitions = Competition.where("...").collect {|i| i.id}
Register.where(:competition_id => competitions)