Let's say I have 2 database tables:
table B is a set of people, table A is a set of people from table B
Table A = (no, id, date) no is PK, id refer to table B
Table B = (id, name) id is PK
My goal is to get data of people (id and name) who didn't attend on a given date (like today for example) the theory seems simple, set of B substract by set of A who attend (in today) but how can I do this in SQL query? I think about first query substracted by second query but got confused.
select * from b where
not exists (select no from A where A.id=B.id and date=#yourdate)
If I understood properly it would be something like this:
select b.id, b.name from tableB b where b.id not in (
select b.id from tableA a
inner join tableB b on a.id = p.id
where a.date = CURRENT_DATE)
Related
I'm trying to select * from two tables (a and b) using a join (column a.id and b.id), given that the count of a column (b.owner) in b is lower than 3, i.e. the occurence of a person's name can be max 2.
I've tried:
SELECT a.*, COUNT(b.owner) AS b_count
FROM a LEFT JOIN b on a.id = b.id
GROUP BY b.owner HAVING COUNT(b_count) <3
As im pretty new to SQL, im pretty stuck here. How can i resolve this issue? The result should be all columns for owners who do not appear more than twice in the data.
The query you are trying to run is not working due to the columns missing in the GROUP BY clause.
As you are outputting all columns from table a (with SELECT a.*), you need to include all those columns in the GROUP BY statement, so that the database understand the group of fields to group by and perform the aggregation required (in your case COUNT(b.owner)).
Example
Considering that your table a has 3 columns below:
CREATE TABLE persons (
id INTEGER,
name VARCHAR(50),
birthday DATE,
PRIMARY KEY (id)
);
.. and your table b the following and referencing the first table as below:
CREATE TABLE sales (
id INTEGER,
person_id INTEGER,
sale_value DECIMAL,
PRIMARY KEY (id),
FOREIGN KEY (person_id) REFERENCES persons(id)
);
.. you should query it aggregating the COUNT() by those 3 columns:
SELECT a.id, a.name, a.birthday, COUNT(b.person_id) AS b_count
FROM persons a
LEFT JOIN sales b ON a.id = b.person_id
GROUP BY a.id, a.name, a.birthday
HAVING COUNT(b.person_id) < 3
Alternative
In case the total of records on the 2nd table is not important to you, you could use a different "strategy" here to avoid performing the JOIN between the tables (useful when joining two huge tables) and rewriting all the columns from a on the SELECT+GROUP BY.
By identifying the records that has less than the 3 occurrences firstly:
SELECT b.person_id
FROM sales b
GROUP BY b.person_id
HAVING COUNT(b.id) < 3;
.. and using it in the WHERE clause to retrieve all the columns from the 1st table only for the ids that resulted from the previous query:
SELECT a.*
FROM persons a
WHERE a.id IN (....other query here....);
.. the execution happens in a more chronological and, perhaps, easier way to visualize while getting more familiar with SQL:
SELECT a.*
FROM persons a
WHERE a.id IN (SELECT b.person_id
FROM sales b
GROUP BY b.person_id
HAVING COUNT(b.id) < 3);
DB Fiddle here
In Standard SQL, you can use:
SELECT a.*, COUNT(b.owner) AS b_count
FROM a LEFT JOIN
b
ON a.id = b.id
GROUP BY a.id
HAVING COUNT(b.owner) < 3;
This may not work in all databases (and it assumes that a.id is unique/primary key). An alternative would be to use a correlated subquery:
SELECT a.*
FROM (SELECT a.*,
(SELECT COUNT(*)
FROM b
WHERE a.id = b.id
) as b_count
FROM a
) a
WHERE b_count < 3;
I have this SQL problem: I have tables A and B. Table A has columns id and name, Table B amount and id which is a foreign key to table A.id.
I need to return all table A rows that don't have their id stored in table B. Any ideas?
So the complete opposite is:
SELECT *
FROM a
LEFT OUTER JOIN b ON a.id = b.id;
Here row what I need is left out of result
Just add a where clause:
SELECT a.*
FROM a LEFT OUTER JOIN
b
ON a.id = b.id
WHERE b.id IS NULL;
You can also use NOT EXISTS:
select a.*
from a
where not exists (select 1 from b where b.id = a.id);
In most databases, the two methods typically have similar performance.
I am wondering how to use oracle sql to get all the rows that are in one table but not another. The issue I am having is that the two tables don't have a field in common so I need to join to a third master table.
This is what I've tried which doesn't produce any errors but also produces 0 records which isn't possible but clearly I've done something wrong.
SELECT a.USER_ID, c.AD_ID, c.CREATED_DATE_ FROM $A$ a, $C$ c, $B$ b
WHERE (b.USER_ID IS NULL AND a.CUSTOMER_ID = c.CUSTOMER_ID)
I have three tables:
Table A has fields CUSTOMER_ID & USER_ID
Table B has field USER_ID
Table C has field CUSTOMER_ID
I need all the users that are in table C but not table B. They are all in Table A because that is the master list of users.
Any insight would be greatly appreciated.
SELECT
*
FROM
table_a
WHERE
NOT EXISTS (SELECT * FROM table_b WHERE table_b.user_id = table_a.user_id )
AND EXISTS (SELECT * FROM table_c WHERE table_c.customer_id = table_a.customer_id)
My solution:
select * from TableC tc
join TableA ta on tc.CUSTOMER_ID=ta.CUSTOMER_ID
left join TableB tb on tb.USER_ID=ta.USER_ID
where ta.USER_ID is null
I think you want:
select a.USER_ID, c.AD_ID, c.CREATED_DATE_
from a join
c
on a.customer_id = c.customer_id
where not exists (select 1 from b where b.user_id = a.user_id);
I have a tables
Table a ( id,name, start_date)
Table b (id(FK to Table a), start_date)
Here is my problem statement:
if id exists in Table b, then select the value of start_date from table b else select the default start_date from table a
I can get the logic working by having 2 seperate queries , my challenge is to achieve it in single query?
Is is possible to achieve in single query?
Try this:
SELECT
a.ID
, COALESCE(b.start_date,a.start_date)
FROM
TableA a
LEFT JOIN
TableB b
ON a.id = b.Id
I have a simple SQL question, I thought it would be quite straight forward but have got myself in a muddle. Any help would be appreciated
I have table A which contains a last updated
Table A has a one to many with Table B
Table B has a one to many with Table C
I want to show all rows of table C with the last updated time from table A. I have tried some joins but they dont seem to be quite working. Ideally I want somehting like
select a.lastUpdated c.* from TableA a, TableC c where
a.id in (select a_id from TableB where (select b_id from TableC where c_id = select
id from TableC where XXXX=YYYY))
so I can pass in an id for table C and then get one row returned with the last updated time present.
XXX=YYY would be my criteria for returning one row of table C.
Any help or pointers appreciated
Thanks
Something like
SELECT c.*
FROM TableA AS a
INNER JOIN TableB AS b
ON a.a_id = b.b_id
INNER JOIN TableC AS c
ON b.b_id = c.c_id
WHERE a.lastUpdated = c.lastUpdated;
Should work. This is a situation where a striaght INNER JOIN should suffice; unless of course I have missed something.
I hope this helps.
You should be able to do this by joining A and B together, aggregating the results at the c_id level, and then joining in C:
select tc.*, maxlastupdated
from tablec tc left outer join
(select tb.c_id, max(lastupdated) as maxlastupdated
from tablea ta join
tableb tb
on ta.b_id = tb.b_id
group by ta.id
) ta
on tc.c_id = ta.c_id
You need to drive your SQL query from Table C.
The query below displays the updated timestamp column from table A.
Since it is a one-to-many in the direction of tables A --> B --> C
You will inevitably end-up with a lot of rows in table C - all with the same timestamp.
SELECT c.*, a1.update_timestamp
FROM table_c c, table_b b, table_a a1
WHERE c.join_column = b.join_column
AND b.join_column = a1.join_column
AND a1.update_timestamp =
(SELECT max(a2.update_timestamp) FROM table_a a2
WHERE a2.<identifying columns> = a1.<identifying columns>
);