I have a table 1
and Table 2
I need to get the following table where the date from table 1 is the closest (i.e. before) to the date from table 2 by id.
I assume I need to join two table where table1.id=table2.id and table1.date<=table2.date and then, rank to get the 'last' record in that merged table? Is it correct? Is there a simpler way?
You can see structure and result in: dbfiddle
select
distinct on (t1.id)
t1.id,
last_value(t1.type) over (order by to_date(t1.date, 'mm/dd/yyyy') desc)
from
table1 t1 inner join table2 t2 on t1.id = t2.id
where
to_date(t1.date, 'mm/dd/yyyy') <= to_date(t2.date, 'mm/dd/yyyy');
Related
how to find number of records in both table using join.
i have two tables table1 and table2 with same structure.
table1
id
item
1
A
1
B
1
C
2
A
2
B
table2
id
item
1
A
1
B
2
A
2
B
2
C
2
D
Output should be like this.
id
table1.itemcount
table2.itemcount
1
3
2
2
2
4
SELECT DISTINCT id, (
SELECT COUNT(*) FROM table1 AS table1_2 WHERE table1_2.id=table1.id
) AS "table1.itemcount", (
SELECT COUNT(*) FROM table2 AS table2_2 WHERE table2_2.id=table1.id
) AS "table2.itemcount"
FROM table1;
Assuming that each id is guaranteed to exist in both tables, the following would work
select
t1.id,
count(distinct t1.item) t1count,
count(distinct t2.item) t2count
from t1
join t2 on t1.id = t2.id
group by 1;
But if that is not guaranteed then we'll have to use full outer join to get unique ids from both tables
select
coalesce(t1.id, t2.id) id,
count(distinct t1.item) t1count,
count(distinct t2.item) t2count
from t1
full outer join t2 on t1.id = t2.id
group by 1;
We're using coalesce here as well for id because if it only exists in t2, t1.id would result in null.
#DeeStark's answer also works if ids are guaranteed to be in both tables but it's quite inefficient because count is essentially run twice for every distinct id in the table. Here's the fiddle where you can test out different approaches. I've prefixed each query with explain which shows the cost
Hope this helps
I have two tables:
main_products
old_products
They have the same info and schema with only one difference:
main_products has min(date) = 2022-01 and max(date) = 2022-05
and
old_products has min(date) = 2020-01 and max(date) = 2020-12
How can I query to get all records from old_products + all records from main_products to get products from 2020-01 to 2022-05 ?
The product on both tables has and product_id field.
I tried to join both tables on product_id but the output is a table with twice number of columns.
select t1.*, t2.* from t1
inner join t2
one t1.product_id = t2.product_id
I think you are looking for a UNION or UNION ALL:
SELECT *
FROM t1
WHERE ...
UNION ALL
SELECT *
FROM t2
WHERE ...
If the columns in t1 and t2 are the same (same number of columns and same types), this will pull the data from both of them. Use UNION if you want duplicates removed or UNION ALL to include duplicates. (In your case it won't make a functional difference since the tables don't overlap by date, but UNION ALL will be faster.)
In the above example, you can put your condition (to only get 2022-01 to 2022-05) in both WHERE conditions. If you don't like repeating the condition, you can use the UNION ALL query in a subquery with the condition outside:
SELECT *
FROM
(
SELECT *
FROM t1
UNION ALL
SELECT *
FROM t2
) sq
WHERE ...
I have Table1 with columns:
Fname,Sname
Table 2 with columns:
Fname,Lname
Now,in a query I want to take all the values from these two tables (First names and last names [Sname in table 1 is Lname]) and return to one columns.
Basically I want to create column to get list of participants which include everyone from these two tables.
Is it possible?
Both the tables are joined indirectly via third table.
You can use UNION ALL will give all the rows from both tables.
SELECT
Fname,
Sname,
CONCAT(Fname,Sname) AS FSname
FROM table1
UNION ALL
SELECT
Fname,
Lname,
CONCAT(Fname,Lname)
FROM table2;
The column names are taken from the first SELECT.
If you use UNION and not UNION ALL rows in table2 which are duplicates of table1 will be omitted, but it can run slower as the values have to be compared.
You can use the third table and LEFT JOIN onto both tables and use COALESCE which returns the first argument which is not null.
SELECT
COALESCE(t1.Fname,t2.Fname),
COALESCE(t1.Sname,t2.Lname),
CONCAT(
COALESCE(t1.Fname,t2.Fname),
COALESCE(t1.Sname,t2.Lname)
) AS FSname
FROM third_table t3
LEFT JOIN table1 t1
ON t1.id = t3.id
LEFT JOIN table2 t2
ON t2.id = te.id;
I have two tables(Table A and Table B) in a Postgres DB.
Both have "id" column in common. Table A has one column called "id" and Table B has three columns: "id, date, value($)".
For each "id" of Table A there exists multiple rows in Table B in the following format - (id, date, value).
For instance, for Table A with "id" as 1 if there exists following rows in Table B:
(1, 2018-06-21, null)
(1, 2018-06-20, null)
(1, 2018-06-19, 202)
(1, 2018-06-18, 200)
I would like to extract the most recent dated non-null value. For example for id - 1, the result should be 202. Please share your thoughts or let me know in case more info is required.
Here is the solution I went ahead with:
with mapping as ( select distinct table1.id, table2.value, table2.date, row_number() over (partition by table1.id order by table2.date desc nulls last) as row_number
from table1
left join table2 on table2.id=table1.id and table2.value is not null
)
select * from mapping where row_number = 1
Let me know if there is scope for improvement.
You may very well want an inner join, not an outer join. If you have an id in table1 that does not exist in table2 or that has only null values you will get NULL for both date and value. This is due to the how outer join works. What it says is if nothing in the right side table matches the ON condition then return NULL for each column in that table. So
with mapping as
(select distinct table1.id
, table2.value
, table2.date
, row_number() over (partition by table1.id order by table2.date desc nulls last) as row_number
from table1
join table2 on table2.id=table1.id and table2.value is not null
)
select *
from mapping
where row_number = 1;
See example of each here. Your query worked because all your test data satisfied the 1st condition of the ON condition. You really need test data that fails to see what your query does.
Caution: DATE and VALUE are very poor choice for a column names. Both are SQL standard reserved words, although not Postgres specifically. Further DATE is a Postgres data type. Having columns with names the same as datatype leads to confusion.
I want to filter out the IDs of Table 1 which is not in between the date range of Table 2.
Table 1:
Booking_ID | starts | ends
Table 2:
ID | starts | ends
Tried to do something like this but it does not fetch the correct results. Seems like something is wrong here.
select t1.id, date(t1.starts), date(t1.ends) from t1
where exists (select *
from t2
where (date(t2.starts) not between date(t1.starts) and date(t1.ends)) or
(date(t2.ends) not between date(t1.starts) and date(t1.ends)) or
(date(t1.starts) not between date(t2.starts) and date(t2.ends))) ```
you can use overlaps for that:
select t1.*
from table1 t1
where exists (select *
from t2
where (t1.starts, t1.ends) overlaps (t2.starts, t2.ends));
If those are timestamp columns and you only want to consider the date values, then cast the values to dates:
select t1.*
from table1 t1
where exists (select *
from t2
where (t1.starts::date, t1.ends::date) overlaps (t2.starts::date, t2.ends::date));
Alternatively you can use a daterange() where it's easier to control if the right hand edge should be included:
select t1.*
from table1 t1
where exists (select *
from t2
where daterange(t1.starts::date, t1.ends::date, '[]') && daterange(t2.starts::date, t2.ends, '[]'))
If you want to exclude e.g. the right edge from the range, use '[)' instead of '[]'