I've got two tables that look like this
TABLE_1
option_id PK,
condition_id FK,
And I has another table that looks like this
TABLE_2
option_id PK, FK -> TABLE_1
condition_id PK, FK
I want to set condition_id in TABLE_1 with corresponding values for condition_id from TABLE_2.
My script looks like this
UPDATE TABLE_1
SET
condition_id = t2.condition_id
FROM TABLE_1 t1
INNER JOIN TABLE_2 t2
ON t1.option_id = t2.option_id
But it seems to be wrong - after the execution all the values of condition_id in TABLE_1 are the same.
What is wrong?
The problem is: you are using two instances of TABLE_1.
UPDATE TABLE_1 <-- first instance
FROM TABLE_1 t1 <-- second instance
Thus, while the FROM allows you to refer to a combined structure that relates matching entries, this forms a full cross join with the instance of TABLE_1 that is being updated. To avoid this you would need to add a further condition like WHERE TU.option_id=t1.option_id. (I introduced TU as an alias for the update target table to avoid ambiguity.)
Or, likely, you might simply use:
UPDATE TABLE_1 t1
SET
condition_id = t2.condition_id
FROM TABLE_2 t2
WHEREt1.option_id = t2.option_id
Something like this should do it :
UPDATE table1
SET table1.condition_id= table2.condition_id
FROM table1 INNER JOIN table2 ON table1.option_id = table2.option_id
Related
I have 2 SQL tables with same column label, Table1 and Table2.
I want to update Table1 with value of Table2 if there is a same value for an attribute.
The tables has CODE, POSITION, DESCRIPTION as columns.
I do this:
UPDATE Table1
SET CODE = Table2.CODE,
POSITION= Table2.POSITION
FROM Table2
WHERE DESCRIPTION = Table2.DESCRIPTION
It works, but if in the DESCRIPTION Value of Table2 is not present into Table1, I want to insert the entire row, in other words I need to do something like:
UPDATE IF DESCRIPTION EXISTS
ELSE INSERT
How can I do this?
You can do this from first-principals in 2 steps
Update the existing values like you have done:
UPDATE Table1
SET
CODE= t2.CODE,
POSITION= t2.POSITION
FROM Table1 t1
INNER JOIN Table2 t2 ON t1.DESCRITPION = t2.DESCRITPION
Then you can insert the missing records
INSERT INTO Table1 (CODE, POSITION, DESCRITPION)
SELECT CODE, POSITION, DESCRITPION
FROM Table2 t2
WHERE NOT EXISTS (SELECT DESCRITPION
FROM Table1 t1
WHERE t1.DESCRITPION = t2.DESCRITPION)
Most RDBMS have a MERGE statement that allows you to combine these two queries into a single atomic operation, you'll need to check the documentation for your vendor, but an MS SQL Server MERGE solution looks like this:
MERGE INTO Table1 AS tgt
USING Table2 AS src
ON tgt.DESCRITPION = src.DESCRITPION
WHEN MATCHED
THEN UPDATE SET CODE= src.CODE,
POSITION= src.POSITION
WHEN NOT MATCHED THEN
INSERT (CODE, POSITION, DESCRITPION)
VALUES (src.CODE, src.POSITION, src.DESCRITPION)
An additional benefit to the MERGE clause is that it simplifies capturing the changed state into the OUTPUT clause which allows for some complex logic all while keeping the query as a single operation without having to manually create and track transaction scopes.
I am using PostgreSQL and Flyway to perform a data migration in an application. The idea is to move rows from one table to another and keep the link between the old and new table in the old table. So, let's say we have Table_1 with columns (id, name, user_id) and a new Table_2 with similiar columns (id2, name2, user_id2).
Now, the first step will be to add a column to Table_1 that will store the id of its counterpart in new Table_2. So:
alter Table_1 add column if not exists migrated_table_2_id int;
And now I would like to write an sql that will perform the migration of data from Table_1 to Table_2 and at the same time fill in the id values in the migrated_table_2_id column. So something like:
insert into Table_2 (name2, user_id2) select name, user_id from Table_1;
but with filling in the migrated_table_2_id with the newly created row in Table 2
You can use a CTE, assuming that name2, user_id2 or both in combination are unique:
with i as (
insert into Table_2 (name2, user_id2)
select name, user_id
from Table_1
returning *
)
update table_1 t1
set t1.user_id2 = t2.id
from table_2 t2
where t2.name = t1.name and t2.user_id2 = t.user_id;
I have a following requirement:
I need to delete records from one table based on the given ID, now this table is referenced by another table and that other table is referenced by yet another table and that last table is also referenced by another table, so I have a chain like this:
table_1 <- table_2 <- table_3 <- table_4
I'm not that experienced with SQL so my solution involves using subqueries to perform this.
I have something like this:
DELETE FROM table_4
WHERE pk_of_table_3 IN
(SELECT id
FROM table_3
WHERE pk_of_table_2 IN
(SELECT id FROM table 2 WHERE pk_of_table_1 = ?
)
)
So this would clear records from table_4 which reference targeted records in table_3.
For table_3 I would do something like:
DELETE FROM table_3
WHERE pk_of_table_2 IN
(SELECT id FROM table_2 WHERE pk_of_table_1 = ?)
Now I move to table_2:
DELETE FROM table_2 WHERE pk_of_table_1 = 5;
So in the end it leaves me with possibility to cleanup necessary records from table_1 since it's not being constrained by anything.
I wanted to ask if this seems like viable solution and if there are better ways to do this?
Do it with a common table expression that chains the DELETE statements:
with delete_t1 as (
delete from table_1
where pk = 42
returning pk
), delete_t2 as (
delete from table_2
where pk_of_table_1 in (select pk from delete_t1)
returning pk
), delete_t3 as (
delete from table_3
where pk_of_table_2 in (select pk from delete_t2)
returning pk
)
delete from table_4
where pk_of_table_3 in (select pk from delete_t3);
If you always do it like that, consider defining the foreign key constraints as on delete cascade, then you only need to delete from table_1 and Postgres will take care of the rest.
I am trying to update a key on a table (t1) when the key value is (abc) by getting the value from table (t2).
It is working as expected when I am limiting it to a specific person
update table_a t1
set t1.u_key = (select t2.u_key
from table_b t2
where t2.name_f=t1.name_f
and t2.name_l=t1.name_l
and rownum<=1
and t2='NEVADA')
where t1.u_key = 'abc'
and e.name_f='Lori'
and e.name_l='U'
;
I initially tried without rownum and it said too many rows returned.
To run on all the data with t1.u_key='abc' and took out the specific name, I tried this which has been running until time out.
update table_a t1
set t1.u_key = (select t2.u_key
from table_b t2
where t2.name_f=t1.name_f
and t2.name_l=t1.name_l
and rownum<=1
and t2='NEVADA')
where t1.u_key = 'abc'
;
Can you please look at it and suggest what am I missing.
You should first take a look what is returned when you run the inner SELECT statement alone:
SELECT t2.u_key FROM table_b t2
WHERE t2.name_f IN (SELECT name_f FROM table_a WHERE u_key = 'abc')
AND t2.name_l IN (SELECT name_l FROM table_a WHERE u_key = 'abc')
AND t2='NEVADA'
Examine the results and you will see that there are more than one row returned.
If there should be only matching row per key, you would need to add the key to the inner SELECT as well but I can't tell you how it should look like without additional table descriptions and possibly some sample entries from table_a and table_b.
Use this:
update (
SELECT t2.u_key t2key,
t1.ukey t1key
FROM table_b t2,
table_a t1
where t2.name_f=t1.name_f
and t2.name_l=t1.name_l
and t2='NEVADA'
and rownum<=1 )
SET t1key = t2key
where t1key = 'abc';
merge into table_a t1
using(
select name_f, name_l, max(u_key) as new_key
from table_b t2
where t2='NEVADA'
group by name_f, name_l
) t2
on (t1.name_f=t2.name_f and t1.name_l=t2.name_l and t1.u_key='abc')
when matched then
update set t1.u_key=t2.new_key
First, SQL is not my strength. So I need help with the following problem. I'll simplify the table contents to describe the problem.
Let's start with three tables : table1 with columns id_1 and value, table2 with columns id_2 and value, and table3 with columns id_3 and value. As you'll notice, a field value appears in all three tables, while ids have different column names. Modifying column names is not an option because they are used by Java legacy code.
I need to set table3.value using table1.value or table2.value according to the fields table1.id_1, table2.id_2 and table3.id_3.
My last attempt, which describes what I try to do, is the following:
UPDATE table3
SET value=(IF ((SELECT COUNT(\*) FROM table1 t1 WHERE t1.id_1=id_3) > 0)
SELECT value FROM table1 t1 WHERE t1.id_1=id_3
ELSE IF ((SELECT COUNT(\*) FROM table2 t2 WHERE t2.id_2=id_3)) > 0)
SELECT value FROM table2 t2 WHERE t2.id_2=id_3)
Here are some informations about the tables and the update.
This update will be included in an XML file used by Liquibase.
It must work with Oracle or SQL Server.
An id from table3.id_3 can be found at most once in table1.id_1 or in table2.id_2, but not in both tables simultaneously.
If table3.id_3 is not found in table1.id_1 nor in table2.id_2, table3.value remains null.
As you can imagine, my last attempt failed. In that case, the IF command was not recognized during the Liquibase update. If anyone has any ideas how to deal with this, I'd appreciate. Thanks in advance.
I don't know Oracle very well, but a SQL Server approach would be the following using COALESCE() and OUTER JOINs.
Update T3
Set Value = Coalesce(T1.Value, T2.Value)
From Table3 T3
Left Join Table2 T2 On T3.Id_3 = T2.Id_2
Left Join Table1 T1 On T3.Id_3 = T1.Id_1
The COALESCE() will return the first non-NULL value from the LEFT JOIN to tables 1 and 2, and if a record was not found in either, it would be set to NULL.
It is Siyual's UPDATE written with MERGE operator.
MERGE into table_1
USING (
SELECT COALESCE(t2.value, t3.value) as value, t1.id_1 as id
FROM table_1 t1, table_2 t2, table_3 t3
WHERE t2.id_2 = t3.id_3 and t1.id_1 = t2.id_2
) t on (table_1.id_1 = t.id)
WHEN MATCHED THEN
UPDATE SET table_1.value = t.value
This should work in Oracle.
In Oracle
UPDATE table3 t
SET value=COALESCE((SELECT value FROM table1 t1 WHERE t1.id_1=t.id_3),
(SELECT value FROM table2 t2 WHERE t2.id_2=t.id_3))
Given your assumption #3, you can use union all to put together tables 1 and 2 without running the risk of duplicating information (at least for the id's of interest). So a simple merge solution like the one below should work (in all DB products that implement the merge operation).
merge into table3
using (
select id_2 as id, value from table2
union all
select id_3, value from table 3
) t
on table3.id_3 = t.id
when matched
then update set table3.value = t.value;
You may want to test the various solutions and see which is most effective for your specific tables.
(Note: merge should be more efficient than the update solution using coalesce, at least when relatively few of the id's in table3 have a match in the other tables. This is because the update solution will re-insert NULL where NULL was already stored when there is no match. The merge solution avoids this unnecessary activity.)