I have Four tables as follows
Review (REV_ID pk , REV_NAME)
Meeting (MEETING_ID pk,MEETING_NAME,REV_ID fk to Review)
Task (TASK_ID pk,TASK_NAME,REV_ID fk to Review)
Answer (ANS_ID pk,ANS_NAME,REV_ID fk to Review)
Now I want to select a particular Review and want to create a table with
Linked meetings
Linked answers
Linked tasks
How shall I proceed with it?
I tried writing join query but I was only able to get data if Rev_ID is present in all tables?
select * from
(SELECT *
FROM meeting
WHERE EXISTS (SELECT *
FROM review WHERE meeting.rev_id
=review.rev_id)
and meeting.rev_id=142),
(SELECT *
FROM answer
WHERE EXISTS (SELECT *
FROM review WHERE answer.rev_id
=rev.rev_id)
and answer.ans_rev_id=142),
(SELECT *
FROM task
WHERE EXISTS (SELECT *
FROM review WHERE task.rev_id
=review.rev_id)
and task.rev_id=142) r;
Note : Here I tried static Rev_ID =142 to check data.
From above query i am getting output only if data exist in all four table, But if Data does not exist in any table, It does not return remaining value.
I want at-least names of all table's in final output.
Try the following, let us know if this meets your requirements.
SELECT rv.rev_id,
rv.rev_name,
mt.meeting_name,
tk.task_name,
ans.ans_name
FROM review rv
LEFT OUTER JOIN meeting mt ON (rv.rev_id = mt.rev_id)
LEFT OUTER JOIN task tk ON (rv.rev_id = tk.rev_id)
LEFT OUTER JOIN answer ans ON (rv.rev_id = ans.rev_id)
WHERE rv.rev_id = 142
SQL Fiddle Demo
If the above SQL is fine, prefix it with create table or view syntax to combine them into one.
Related
Hi guys I'm new with databases and I'm trying to make a query where I join 3 tables. I could make it and I want to clean up the result. I want to know how can I delete the column "pin" from users table and maybe some "ids" columns.
Select * from "wish-list"
Join products
On "wish-list".id = products.holiday_id
Join users
On "wish-list".user_id = users.id
Where "wish-list".id = 1
You need to specify which columns you really need in your output. At the moment you are using
SELECT * which outputs all columns of all joined tables.
Here is what it should look like:
SELECT holiday, products.description, users.pin FROM "wish-list"
JOIN products ON "wish-list".id = products.holiday_id
JOIN users ON "wish-list".user_id = users.id
WHERE "wish-list".id = 1
It's important that you reference all columns which are not your main entity (here wish-list) with tablename.column (products.description and not only description). It will work without referencing strictly but only if the column name is unique in your query.
Furthermore you can rename columns. This is useful for example if you want to get the id's of the product table and the wish-list table.
SELECT product.id AS product_id, id AS wishlist_id FROM "wish-list"
...
Hope that helps!
I am using sql server management studio 2012. Please tae a minute or two to understand this problem, It's really important:(
The scenario is :
I have three table, Patient, patientAccount and Message.
Now, I am inserting values into tables Patient and Message first, and then after some time I am inserting values into PatientAccount Table.Now, the problem is in the software i am using sql with) i had this query:
select
*
from Patient
join Message on Patient.GUID = Message.PatientGUID
where Message.GUID = "..Data
and if I add PatientAccount in this query as well, like
select
*
from Patient
join Message on Patient.GUID = Message.PatientGUID, PatientAccount
where Message.GUID = "..Data
It becomes mandatory to add values to the PatientAccount table at the same moment when I am adding them to Patient and Message table, but what I really want is values to be taken up by query if there is data in the PatientAccount table, and if there is no values inserted into patientAccount table, It should pick up values from Patient and Message table only.
and I want all of it in one query.
You can use an outer join for this purpose so that the select query doesn't depend on the PatientAccount table. Similar to the query below
SELECT *
FROM patient p
LEFT JOIN patientaccount pa
ON p.guid = pa.patientguid
LEFT JOIN message m
ON p.guid = m.patientguid
WHERE m.guid = "id"
This select query will always return records from the PatientAccount table but if there's no data for a specific Patient then the columns from the PatientAccount will be null
Hi am I am creating a database which allows users to make a reservation to a restaurant. Below is my data model for the database.
My question is i am a little confused with how i would check for tables that are available on a given night. The restaurant has 15 tables for any night with 4 people to a table (Groups can be 4 - 6 big, groups larger than 4 will take up two tables).
How would i query the database to return the tables which are available on a given night.
Thanks.
EDIT::
This is what i have tried. (Some of it is pseudo as i am not quite sure how to do it)
SELECT tables.table_id
FROM tables
LEFT JOIN table_allocation
ON tables.table_id = table_allocation.table_id
WHERE table_allocation.table_id is NULL;
This returns the well empty rows as it is checking for the none presence of the table. I am not quite sure how i would do the date bit test.
To find TABLE rows that have no TABLE_ALLOCATION rows on a given THEMED_NIGHT.TEME_NIGHT_DATE, you should be able to do something like this:
SELECT *
FROM TABLES
WHERE
TABLE_ID NOT IN (
SELECT TABLE_ALLOCATION.TABLE_ID
FROM
TABLE_ALLOCATION
JOIN RESERVATION
ON TABLE_ALLOCATION.RESERVATION_ID = RESERVATION.RESERVATION_ID
JOIN THEMED_NIGHT
ON RESERVATION.THEME_ID = THEMED_NIGHT.THEME_ID
WHERE
THEME_NIGHT_NAME = :the_date
)
In plain English:
Join TABLE_ALLOCATION, RESERVATION and THEMED_NIGHT and accept only those that are on the given date (:the_date).
Discard the TABLE rows that are related to the tuples above (NOT IN).
Those TABLE rows that remain are free for the night.
Try:
SELECT tables.table_id
FROM tables t
WHERE NOT EXISTS
(SELECT NULL
FROM table_allocation a
JOIN reservation r
ON a.reservation_id = r.reservation_id and
r.`TIME` between :Date and :Date+1
WHERE t.table_id = a.table_id)
Note: will only return tables that are not booked at any point on the day in question.
i hava a set of following tables
customer(cus_id,cus_name);
jointAccount(cus_id,acc_number,relationship);
account(acc_number,cus_id)
now i want to create a select statement to list all the jointAccounts,
it should included the both customer name, and relationship.
I have no idea how to retrieve both different user name, is that possible to do this?
Generally speaking, yes. I'm assuming you mean you want to get customer info for both sides of the joint account per your jointAccount table. Not sure what database you're using so this answer is assuming MySQL.
You can join on the same table twice in a single SQL query. I'm assuming you have not yet created your tables, as you have cus_id listed twice in the jointAccount table. Typically these would be something like cus_id1 and cus_id2, which I've used in my sample query below.
Example:
SELECT c1.cus_id AS cust1_id, c1.cus_name AS cust1_name
, c2.cus_id AS cust2_id, c2.cus_name AS cust2_name, j.relationship
FROM customer c1
INNER JOIN jointAccount j
ON c1.cus_id = j.cus_id1
, customer c2
INNER JOIN jointAccount j
ON c2.cus_id = j.cus_id2
I haven't tested this but that's the general idea.
try this query:
SELECT * FROM jointAccount a LEFT JOIN customer c ON a.cus_id = c.cus_id;
just replace the * with the name of the columns you need.
I have been using SQL for years, but have mostly been using the query designer within SQL Studio (etc.) to put together my queries. I've recently found some time to actually "learn" what everything is doing and have set myself the following fairly simple tasks. Before I begin, I'd like to ask the SOF community their thoughts on the questions, possible answers and any tips they may have.
The questions are;
Find all records w/ a duplicate in a particular column (e.g. a linking id is in more than 1 record throughout table)
SUM price from a linked table within the same query (select within a select?)
Explain the difference between the 4 joins; LEFT, RIGHT, OUTER, INNER
Copy data from one table to another based on SELECT and WHERE criteria
Input welcomed & appreciated.
Chris
I recommend that you start by following some tutorials on this topic. Your questions are not uncommon questions for someone moving from a beginner to intermediate level in SQL. SQLZoo is an excellent resource for learning SQL so consider following that.
In response to your questions:
1) Find all records with a duplicate in a particular column
There are two steps here: find duplicate records and select those records. To find the duplicate records you should be doing something along the lines of:
select possible_duplicate_field, count(*)
from table
group by possible_duplicate_field
having count(*) > 1
What we're doing here is selecting everything from a table, then grouping it by the field we want to check for duplicates. The count function then gives me a count of the number of items within that group. The HAVING clause indicates that we want to filter AFTER the grouping to only show the groups which have more than one entry.
This is all fine in itself but it doesn't give you the actual records that have those values on them. If you knew the duplicate values then you'd write this:
select * from table where possible_duplicate_field = 'known_duplicate_value'
We can use the SELECT within a select to get a list of the matches:
select *
from table
where possible_duplicate_field in (
select possible_duplicate_field
from table
group by possible_duplicate_field
having count(*) > 1
)
2) SUM price from a linked table within the same query
This is a simple JOIN between two tables with a SUM of the two:
select sum(tableA.X + tableB.Y)
from tableA
join tableB on tableA.keyA = tableB.keyB
What you're doing here is joining two tables together where those two tables are linked by a key field. In this case, this is a natural join which operates as you would expect (i.e. get me everything from the left table which has a matching record in the right table).
3) Explain the difference between the 4 joins; LEFT, RIGHT, OUTER, INNER
Consider two tables A and B. The concept of "LEFT" and "RIGHT" in this case are slightly clearer if you read your SQL from left to right. So, when I say:
select x from A join B ...
The left table is "A" and the right table is "B". Now, when you explicitly say "LEFT" the SQL statement you are declaring which of the two tables you are joining is the primary table. What I mean by this is: Which table do I scan through first? Incidentally, if you omit the LEFT or RIGHT, then SQL implicitly uses LEFT.
For INNER and OUTER you are declaring what to do when matches don't exist in one of the tables. INNER declares that you want everything in the primary table (as declared using LEFT or RIGHT) where there is a matching record in the secondary table. Hence, if the primary table contains keys "X", "Y" and "Z", and the secondary table contains keys "X" and "Z", then an INNER will only return "X" and "Z" records from the two tables.
When OUTER is used, we're saying: Give me everything from the primary table and anything that matches from the secondary table. Hence, in the previous example, we'd get "X", "Y" and "Z" records in the output record set. However, there would be NULLs in the fields which should have come from the secondary table for key value "Y" as it doesn't exist in the secondary table.
4) Copy data from one table to another based on SELECT and WHERE criteria
This is pretty trivial and I'm surprised you've never encountered it. It's a simple nested SELECT in an INSERT statement (this may not be supported by your database - if not, try the next option):
insert into new_table select * from old_table where x = y
This assumes the tables have the same structure. If you have different structures then you'll need to specify the columns:
insert into new_table (list, of, fields)
select list, of, fields from old_table where x = y
Let's say you have 2 tables named :
[OrderLine] with the columns [Id, OrderId, ProductId, Qty, Status]
[Product] with [Id, Name, Price]
1) all orderline of command having more than 1 line (it's technically the same as looking for duplicates on OrderId :) :
select OrderId, count(*)
from OrderLine
group by OrderId
having count(*) > 1
2) total price for all order line of the order 1000
select sum(p.Price * ol.Qty) as Price
from OrderLine ol
inner join Product p on ol.ProductId = p.Id
where ol.OrderId = 1000
3) difference between joins:
a inner join b => take all a that has a match with b. if b is not found, a will be not be returned
a left join b => take all a, match them with b, include a even if b is not found
a righ join b => b left join a
a outer join b => (a left join b) union ( a right join b)
4) copy order lines to a history table :
insert into OrderLinesHistory
(CopiedOn, OrderLineId, OrderId, ProductId, Qty)
select
getDate(), Id, OrderId, ProductId, Qty
from
OrderLine
where
status = 'Closed'
To answer #4 and to perhaps show at least some understanding of SQL and the fact this isn't HW, just me trying to learn best practise;
SET NOCOUNT ON;
DECLARE #rc int
if #what = 1
BEGIN
select id from color_mapper where product = #productid and color = #colorid;
select #rc = ##rowcount
if #rc = 0
BEGIN
exec doSavingSPROC #colorid, #productid;
END
END
END