I have two unrelated tables that I want to do an LEFT JOIN on, I only want 1 column from the LEFT table but the entire entity (which I intend to update if its present or create if not) from the right.
Simplified version of tables:
TABLE1
id, type, data
TABLE2
id, type, and, other, stuff
Current JPQL:
SELECT T1.type,
(SELECT T2
FROM TABLE2 T2
WHERE T2.id = T1.id
AND T2.type = T1.type)
FROM T1
WHERE T1.id = :ID
I am currently getting some sort of logical union error...
Can this been done or should I just use separate queries?
The exact exception is:
Caused by: java.lang.ClassCastException: org.apache.openjpa.jdbc.sql.LogicalUnion$UnionSelect incompatible with org.apache.openjpa.jdbc.sql.SelectImpl
The Java code I use follows:
Query q = this.em.createQuery(jql, Tuple.class);
q.setParameter("ID", id);
#SuppressWarnings("unchecked")
List<Tuple> result = q.getResultList();
The subquery is not essential to my solution - it's just the only form that was parseable - a regular SQL LEFT JOIN wasn't. In words what I am trying to do is for a given ID in TABLE1 find all rows in TABLE2 that have the same ID and type or null if there is no row. Later code will create rows in TABLE2 where there are none for the id and type. I'm expecting 2-3 types per ID in TABLE1 and about half the time for a matching row in TABLE2.
Related
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 a scenario to extract information from three(Table1, Table2, Table4) tables based on the common id of Table1
For extracting information from Table 4, I have to look another intermediate table(Table3) for the common Id between Table 3 and Table 4. The query result of Table 4 information would contain more than a single row as query response.
I have written the following HQL(Hibernate Query) for my requirement
select t1,t2,(select t4.column1 from Table4 t4
join Table3 t3 on t4.column0=t3.column0 and t3.column1=t1 and t3.column2='desired_value') from Table1 t1
join Table2 t2 on t2.column1=t1.column1
where t1.column0=:id and t1.column3=:value
I have entity classes for all the four tables.
How can I select the multiple rows from the subquery
What is the euiquvalent of POSTGRESQL array_agg() / string_agg() method in Spring Data JPA?
Without the subquery, I am able to fetch Object[] response with my Entity class objects.
How can I add my subquery in order to retrieve all my desired data in a Single transaction without creating a separate query method in my Repository class?
What I tried so far:
select t1,t2,(select new List(t4.column1) from Table4 t4
join Table3 t3 on t4.column0=t3.column0 and t3.column1=t1 and t3.column2='desired_value') from Table1 t1
join Table2 t2 on t2.column1=t1.column1
where t1.column0=:id and t1.column3=:value
Below is the output object that I am trying to achieve:
List<Object[]> as my query response
where each Object[] will be of size 3 with following
Object[0] -> Table1_Entity object
Object[1] -> Table2_Entity object
Object[2] -> will be a String[] containing a specific column values from Table4 Entity class
i.e response = [[obj1, obj2, ["value1, value2","value3"]], [obj3, obj4, ["value1, value2","value3"]], ......]
Try this:
select t1,t2, (select cast(function('string_agg', t4.column1, ', ') as string) from Table4 t4
join Table3 t3 on t4.column0=t3.column0 and t3.column1=t1 and t3.column2='desired_value') from Table1 t1
join Table2 t2 on t2.column1=t1.column1
where t1.column0=:id and t1.column3=:value
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 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
My basic question has to do with updating multiple columns at once from specified values in my query. The reason I want to do this is that I am updating my values from a ginormous table so I only want to query it once in order to reduce run time. Here is an example of an example select statement that returns the value I want for just one of the columns I need to update:
select a.Value
from Table1
left outer join
(
select ID, FilterCol1, FilterCol2, Value
from Table2
) a on a.ID = Table1.ID
where {Condition1a on FilterCol1}
and {Condition2a on FilterCol2}
In order to update multiple columns at once I would like to be able do something like this (but it returns NULL):
Update T1
set T1Value1 = (select a.Value where {Condition1a on FilterCol1}
and {Condition2a on FilterCol2)
,T1Value2 = (select a.Value where {Condition1b on FilterCol1}
and {Condition2b on FilterCol2})
from Table1 T1
left outer join
(
select ID, FilterCol1, FilterCol2, Value
from Table2
) a on a.ID = Table1.ID
Any help figuring this out would be greatly appreciated, let me know if you have any questions or if I made any errors. Thanks!
EDIT: I think I have identified the problem, but I'm not sure of a solution yet. I think seeing the issue requires a little more context: The select from table 2 is actually an unpivot on a wide table. This means that when the left outer join is applied, there will be multiple rows for a given ID. What the case statement that Earl suggested seems to be doing (and I assume this is happening with the where clause as well) is comparing my Conditions to only the first row of the columns from a. Since my conditions are meant to help determine which of the rows from a is chosen, they will always evaluate false for the first row (I know this just from what I know about the data), hence my perpetual NULL values. Does anyone know of a workaround to look at the other rows in a?
UPDATE T1
SET T1Value1 = CASE WHEN (FilterCol1 = Condition1a AND FilterCol2 = Condition2a) THEN a.Value END,
T1Value2 = CASE WHEN (FilterCol1 = Condition1b AND FilterCol2 = Condition2b) THEN a.Value END
FROM Table1 T1
left outer join
(
select ID, FilterCol1, FilterCol2, Value
) a on a.ID = Table1.ID