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;
Related
I want to check if tables table_a and table_b are identical. I thought I could full outer join both tables on all columns and count the number of rows and missing values. However, both tables have many columns and I do not want to explicitly type out every column name.
Both tables have the same number of columns as well as names. How can I full outer join both of them on all columns without explicitly typing every column name?
I would like to do something along this syntax:
select
count(1)
,sum(case when x.id is null then 1 else 0 end) as x_nulls
,sum(case when y.id is null then 1 else 0 end) as y_nulls
from
x
full outer join
y
on
*
;
You can use NATURAL FULL OUTER JOIN here. The NATURAL key word will join on all columns that have the same name.
Just testing if the tables are identical could then be:
SELECT *
FROM x NATURAL FULL OUTER JOIN y
WHERE x.id IS NULL OR y.id IS NULL
This will show "orphaned" rows in either table.
You might use except operators.
For example the following would return an empty set if both tables contain the same rows:
select * from t1
except
select * from t2;
If you want to find rows in t1 that are different to those in t2 you could do
select * from t1
where not exists (select * from t1 except select * from t2);
Provided the number and types of columns match you can use select *, the tables' columns can vary in names; you could also invert the above and union to return combined differences.
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 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');
Assuming I have a table with 3 columns, ID, Name, City and I want to use named query to return rows with unique city..can it be done?
Are you asking whether it is possible to write a query that will return the cities that appear in exactly one row, in a table that has ID/Name/City triplets where there could be multiple rows for the same city but with different names?
If so, it would depend on the database engine behind the scenes - but you could try things like:
with candidates (city, num) as (
select city, count(*) from table
group by city
)
select city from candidates where num = 1
Or
select t1.city from table t1
where not exists (
select * from table t2
where t2.city = t1.city and t2.id <> t1.id
)
where table is your table with these triplets.
I have two table with one of them is vertical i.e store only key value pair with ref id from table 1. i want to join both table and dispaly key value pair as a column in select. and also perform sorting on few keys.
T1 having (id,empid,dpt)
T2 having (empid,key,value)
select
T1.*,
t21.value,
t22.value,
t23.value,
t24.value
from Table1 t1
join Table2 t21 on t1.empid = t21.empid
join Table2 t22 on t1.empid = t22.empid
join Table2 t23 on t1.empid = t23.empid
where
t21.key = 'FNAME'
and t22.key = 'LNAME'
and t23.key='AGE'
The query you demonstrate is very inefficient (another join for each additional column) and also has a potential problem: if there isn't a row in T2 for every key in the WHERE clause, the whole row is excluded.
The second problem can be avoided with LEFT [OUTER] JOIN instead of [INNER] JOIN. But don't bother, the solution to the first problem is a completely different query. "Pivot" T2 using crosstab() from the additional module tablefunc:
SELECT * FROM crosstab(
'SELECT empid, key, value FROM t2 ORDER BY 1'
, $$VALUES ('FNAME'), ('LNAME'), ('AGE')$$ -- more?
) AS ct (empid int -- use *actual* data types
, fname text
, lname text
, age text);
-- more?
Then just join to T1:
select *
from t1
JOIN (<insert query from above>) AS t2 USING (empid);
This time you may want to use [INNER] JOIN.
The USING clause conveniently removes the second instance of the empid column.
Detailed instructions:
PostgreSQL Crosstab Query