These two requirements must be met:
Select products that have the status "waiting".
The last e-mail must have been sent 3 days ago.
The following tables and columns are given:
products: id, name, status_id, notification
status: id, name
emaillogs: id, product_id, subject, text, date_created
I tried the following:
SELECT
product.id
FROM
product
LEFT JOIN
status ON product.status_id = status.id
INNER JOIN
emaillog ON product.id = emaillog.product_id
AND (emaillog.date_created <= '2018-11-04 16:32:49')
WHERE
(status.name = 'waiting' AND product.notification = 1)
GROUP BY emaillog.product_id
This works only if there are records in the emaillogs table. If there are no records in the emaillogs table, the products should nevertheless be selected.
Use LEFT JOIN rather than ordinary inner JOIN if you want to preserve unjoined rows in your result set. But, beware, mentioning a column from a left-joined table in your WHERE clause converts the left join to an inner join.
Related
Iam currently trying to left join a table on a left joined table as follows.
I have the tables:
accounts (id, vorname, nachname)
projektkurse (id, accounts_id, projektwochen_id)
projektkurs_einzel (id, projektkurse_id)
projektkurs_einzel_zeiten (id, date, shift, projektkurs_einzel_id)
Now I want to get every account and the amount times they have an entry inside of projektkurs_einzel_zeiten, which should also be unique. So having the same date and shift multiple times does not count as multiple entries. The result should also be limited by the column projektwochen_id from the table projektkurse. This column should match a certain value for example 8.
Some Accounts don't have any entries in projektkurse, projektkurs_einzel and projektkurs_einzel_zeiten, this is why my first thought was using LEFT JOIN like this:
SELECT accounts.id, accounts.vorname, accounts.nachname, COUNT(DISTINCT projektkurs_einzel_zeiten.date, projektkurs_einzel_zeiten.shift) AS T
FROM accounts
LEFT JOIN projektkurse on accounts.id = projektkurse.creator_id
LEFT JOIN projektkurs_einzel on projektkurse.id = projektkurs_einzel.projektkurs_id
LEFT JOIN projektkurs_einzel_zeiten ON projektkurs_einzel.id = projektkurs_einzel_zeiten.projektkurs_einzel_id
WHERE projektkurse.projektwochen_id = 8
GROUP BY accounts.id
This query does not achieve exactly what I want. It only returns accounts that have atleast one entry in projektkurse even if they have none in projektkurs_einzel and projektkurs_einzel_zeiten. The Count is obviously 0 for them but the accounts that have no entries in projektkurse are being ignored completly.
How can I also show the accounts that don't have entries in any other table with the Count 0 aswell?
I would recommend writing the query like this:
SELECT a.id, a.vorname, a.nachname,
COUNT(DISTINCT pez.date, pez.shift) AS T
FROM accounts a LEFT JOIN
projektkurse
ON a.id = pk.creator_id AND
pk.projektwochen_id = 8 LEFT JOIN
projektkurs_einzel pe
ON pk.id = pe.projektkurs_id LEFT JOIN
projektkurs_einzel_zeiten pez
ON pe.id = pez.projektkurs_einzel_id
GROUP BY a.id, a.vorname, a.nachname;
Notes:
Your problem is fixed by moving the WHERE condition to the ON clause. Your WHERE turns the outer join into an inner join, because NULL values do not match.
Table aliases make the query easier to write and to read.
It is a best practice to include all unaggregated columns in the GROUP BY. However, assuming that id is unique, your formulation is okay (due to something called "functional dependencies").
You should not use eft join table's column ins where condition this work as inner join
You should move the where condition for a left joined table in the corresponding ON clause
SELECT accounts.id, accounts.vorname, accounts.nachname, COUNT(DISTINCT projektkurs_einzel_zeiten.date, projektkurs_einzel_zeiten.shift) AS T
FROM accounts
LEFT JOIN projektkurse on accounts.id = projektkurse.creator_id
AND projektkurse.projektwochen_id = 8
LEFT JOIN projektkurs_einzel on projektkurse.id = projektkurs_einzel.projektkurs_id
LEFT JOIN projektkurs_einzel_zeiten ON projektkurs_einzel.id = projektkurs_einzel_zeiten.projektkurs_einzel_id
GROUP BY accounts.id
I have the following query:
SELECT
usp.user_id AS userId,
usp.create_time AS create_time,
ml.amount AS amount
FROM user_subscription_plan AS usp
RIGHT JOIN product AS product ON product.id = usp.product_id
LEFT JOIN modification_log AS ml ON ml.subscription_id = usp.id
WHERE usp.id IN ('447482')
I have three tables, from which I need to select data.
My problem begins with the last LEFT join.
modification_log table could have no entries, but also it could have more entries.
I want to select only the latest entry. With the above query, if I have 2 (or more) entries in the modification_log, I receive 2 identical results (repeated).
What I would like to get:
If there are no results in the modification_log, then it will return null. I think that is covered with LEFT JOIN. But also, in the case of many record, I would need to select the latest added one (amount)
I believe I might need a sub-query, but I fail to implement it.
You have to use a subquery for taking left join with modification_log table as
SELECT
usp.user_id AS userId,
usp.create_time AS create_time,
ml.amount AS amount
FROM user_subscription_plan AS usp
RIGHT JOIN product AS product ON product.id = usp.product_id
LEFT JOIN
(select * modification_log where subscription_id
IN ('447482') order by created_at desc LIMIT 1)
AS ml ON ml.subscription_id = usp.id
WHERE usp.id IN ('447482')
Note that the where clause in subquery select * modification_log where subscription_id IN ('447482')
is the same as with the last where condition
Just add a max condition after your left join to get the latest entry to be joined, like below-
LEFT JOIN modification_log AS ml ON ml.subscription_id = usp.id
where usp.id IN ('447482') and ml.id = (select max(id) from modification_log)
TABLE user
- id
- username
- email
- passwd
TABLE user_external
- id
- username
- email
- passwd
TABLE orders
- id
- user_id
- product
I have two tables containg userinformation i want to merge in order to get usersname on a order.
my select only fetches the name from the user table (and leaves the ones from external blank), but not the user_external.
Is there a way to UNION users tables, and then do a left join?
select
orders.product,
merged_user_table.name as name
FROM orders o
LEFT JOIN merged_user_table user_assigned_to ON o.user_id = merged_user_table.id
WHERE
orders.id = 1
The following should work:
SELECT
orders.product
,merged_user_table.name as name
FROM orders o
LEFT JOIN (
SELECT id,username,email,passwd
FROM user
UNION ALL
SELECT id,username,email,passwd
FROM user_external
) merged_user_table user_assigned_to
ON o.user_id = merged_user_table.id
WHERE
orders.id = 1
I have assumed that the user and user_external tables' users are distinct. Using UNION without ALL will effectively perform a SELECT DISTINCT between the two selects in the subquery, which would be less efficient.
While you can use a sub query the get a unioned table, then join that to orders, this does mean the main join won't use an index.
As such I would probably use 2 separate queries, one joining orders with user and the other joining orders with user_external, and union the results together.
This should work (using an INNER JOIN rather than a LEFT OUTER JOIN - can't see why you are using a LEFT OUTER JOIN but there might be a reason). You have specified to bring back a column called name, but neither user table has such a column so not sure if you mean to bring back the user name or the table name - so the below example SQL brings back both.
SELECT orders.product,
user.username as name,
'user' as table_name
FROM orders o
INNER JOIN user
ON o.user_id = user.id
WHERE orders.id = 1
UNION ALL
SELECT orders.product,
user_external.username as name,
'user_external' as table_name
FROM orders o
INNER JOIN user_external
ON o.user_id = user_external.id
WHERE orders.id = 1
What i would like to archieve:
Getting the correct sum of the total amount of the orders that has been cancelled of user id 2002.
Some pre information:
I am having deals which that has its price in deals.price and its id in deals.ID
I then have orders with a foreign key to deals.ID
Running this SQL:
select SUM(deals.price), orders.* from orders
JOIN deals ON deals.ID = orders.deal_id
where orders.user_id = 2002
and orders.cancelled = 1
Works just fine.
Here is where i get stuck:
As an addition to deals, each deals has products with their own prices.
Table is called deal_products, deal_products.price hold the price and deal_products.product_id has the ID of it.
A order is attached to a deal product in another table called order_products, where order_products.product_id = deal_products.product_id
To sum up: I would like to do is including a if inside the above SQL.
If a order has a row in order_products, get the order_products.product_id and find the price in deal_products (price) and use this instead of deals.price when SUM()'ing.
If there is no row it should use deals.price.
How can this be archieved? To first look in another table if there is a entry, and then further look in to a third table and get a value to use?
You can use COALESCE + LEFT JOIN:
select SUM(coalesce(dp.price, d.price)), o.*
from orders o JOIN deals d ON d.ID = o.deal_id
LEFT JOIN order_products op on op.order_id = o.id
LEFT JOIN deal_products dp on op.product_id = dp.product_id
where o.user_id = 2002 and o.cancelled = 1
group by ...;
COALESCE function returns first not null operand
LEFT [OUTER] JOIN = [INNER] JOIN + all rows of the structure on the left side of the LEFT JOIN keyword, which don't match the ON clause in the right structure.
Having 5 tables
Table a_dates = id,
Table b_types = id, a_date_id, c_type_id,
Table c_types = id, name,
Table d_profiles = id, name, profile_type
Table e_ps = id, a_date_id, d_profile_id
From a_dates Need to get b_types,...then from b_types needs c_types name,... Then compare c_types name with d_profiles name and get d_profiles id.... if equals then create a records in e_ps with a_date_id, d_profile_id.
Could any one please help me in getting the query from inner join.
I tried like, it is incomplete query
INSERT INTO e_ps(id,a_date_id,a_date_type,d_profile_id,c_id)
SELECT '',a.id,'A',dp.id,'67' FROM d_profiles dp
INNER JOIN a_dates a ON {HERE I NEED NAME MATCHING WITH c_types name} = dp.name and dp.profile_type = 'A'
INNER JOIN a_dates ON a.id = a_dates.id
LEFT OUTER JOIN e_ps eps ON eps.a_date_type = 'A' AND eps.a_date_id = a_dates.id
WHERE eps.a_date_id IS NULL
This seems to be a relatively simple JOIN:-
INSERT INTO e_ps(id, a_date_id, d_profile_id)
SELECT NULL, a_dates.id, d_profiles.id
FROM a_dates
INNER JOIN b_types ON a_dates.id = b_types.a_date_id
INNER JOIN c_types ON b.c_type_id = c.id
INNER JOIN d_profiles ON c_types.name = d_profiles.name
With joins there are several types, and I suspect you are getting confused. Briefly:-
With an INNER JOIN it looks for a match that is on BOTH tables. If no
match the no record is returned.
With a LEFT OUTER JOIN it takes a record from the table on the left
and looks for a match on the table on the right. If a match great,
but if not then it still brings a row back but the columns from the
table on the right just have values of NULL.
A RIGHT OUTER JOIN is very much the same, just with the tables
reversed (most people including me avoid using this as it has no
advantages most of the time but just makes things confusing).
With a FULL OUTER JOIN it gets the records from both side, whether
they match or not. If they match then the columns from both are
returned, if not matched then the columns from one are returned. Not
that MySQL does not support a FULL OUTER JOIN (although there are
ways to emulate it).
A CROSS JOIN joins every combination of 2 tables. These are used when
there is no common column to match on but you want all combinations.
For example if you wanted a table of all employees and all days of
the week for each employee you would cross join a table of days of
the week against a table of employees (then for useful data you might
LEFT OUTER JOIN a table of holidays to the result).