I am currently trying to delete from Table A where a corresponding record is not being used in Table B. Table A has Section, SubSection, Code, Text as fields, where the first three are the Primary Key. Table B has ID, Section, SubSection, Code as fields, where all four are the Primary Key. There are more columns, but they are irrelevant to this question...just wanted to point that out before I get questioned on why all columns are part of the Primary Key for Table B. Pretty much Table A is a repository of all possible data that can be assigned to a entity, Table B is where they are assigned. I want to delete all records from table A that are not in use in Table B. I have tried the following with no success:
DELETE FROM Table A
WHERE NOT EXISTS (SELECT * from Table B
WHERE A.section = B.section
AND A.subsection = B.subsection
AND A.code = b.code)
If I do a Select instead of a delete, I get the subset I am looking for, but when I do a delete, I get an error saying that there is a syntax error at Table A. I would use a NOT IN statement, but with multiple columns being part of the Primary Key, I just don't see how that would work. Any help would be greatly appreciated.
In sql server,when using not exists, you need to set an alias for the table to be connected, and in the delete statement, to specify the table to delete rows from.
DELETE a FROM Table_A a
WHERE NOT EXISTS (SELECT * from Table_B b
WHERE a.section = b.section
AND a.subsection = b.subsection
AND a.code = b.code)
Please try :
DELETE FROM Table A
WHERE NOT EXISTS (SELECT 1 from Table B
WHERE A.section = B.section
AND A.subsection = B.subsection
AND A.code = b.code)
1 is just a placeholder, any constant/single non-null column will work.
Try something like this:
delete from Table_A
where (section, subsection, code) not in (select section,
subsection,
code
from Table_B)
Related
I used a query to find a list of Primary Keys. One Primary key per each ForiegnKey in a table by using below query.
select foreignKey, min(primaryKey)
from t
group by foreignKey;
Let us say this is the result : 1,4,5
NOw I have another table - Table B that has list of all Primary keys. It has 1,2,3,6,7,8,9
I want a write a query using the above query So that I get a subset of the original query(above) that does not exist in Table B. I want 4 and 5 back with the new query.
Use a having clause:
select foreignKey, min(primaryKey)
from t
group by foreignKey
having min(primarykey) not in (select pk from b);
You should also be able to express this as not exists:
having not exists (select 1
from b
where b.pk = min(t.primaryKey)
)
I am using sqlite3.
I have one "currencies" table, and two tables that reference the currencies table using a foreign key, as follows:
CREATE TABLE currencies (
currency TEXT NOT NULL PRIMARY KEY
);
CREATE TABLE table1 (
currency TEXT NOT NULL PRIMARY KEY,
FOREIGN KEY(currency)
REFERENCES currencies(currency)
);
CREATE TABLE table2 (
currency TEXT NOT NULL PRIMARY KEY,
FOREIGN KEY(currency)
REFERENCES currencies(currency)
);
I would like to make sure that rows in the "currencies" table that are not referenced by any row from "table1" and "table2" will be removed automatically. This should behave like some kind of ref-counted object. When the reference count reaches zero, the relevant row from the "currencies" table should be erased.
What is the "SQL way" to solve this problem?
I am willing to redesign my tables if it could lead to an elegant solution.
I prefer to avoid solutions that require extra work from the application side, or solutions that require periodic cleanup.
Create an AFTER DELETE TRIGGER in each of table1 and table2:
CREATE TRIGGER remove_currencies_1 AFTER DELETE ON table1
BEGIN
DELETE FROM currencies
WHERE currency = OLD.currency
AND NOT EXISTS (SELECT 1 FROM table2 WHERE currency = OLD.currency);
END;
CREATE TRIGGER remove_currencies_2 AFTER DELETE ON table2
BEGIN
DELETE FROM currencies
WHERE currency = OLD.currency
AND NOT EXISTS (SELECT 1 FROM table1 WHERE currency = OLD.currency);
END;
Every time that you delete a row in either table1 or table2, the trigger involved will check the other table if it contains the deleted currency and if it does not contain it, it will be deleted from currencies.
See the demo.
There is no automatic way of doing this. The reverse can be handling using cascading delete foreign key references. The reverse is that when a currency is deleted all related rows are.
You could schedule a job daily running something like:
delete from currencies c
where not exists (select 1 from table1 t1 where t1.currency = c.currency) and
not exists (select 1 from table2 t2 where t2.currency = c.currency);
If you need an automatic way for doing that, then most dbms provide a trigger mechanism. You can create a trigger on update and delete operations that run the folowing query:
you can use a left join for that:
https://www.w3schools.com/sql/sql_join_left.asp
It return a row for all rows from the left table, even if there is no corresponding row in the right table, replacing the rows form the right with null. You can then check a not null right table field for null with is null. This will filter for the rows the have no counterpart in the right table.
For example:
SELECT currencies.currency FROM currencies LEFT JOIN table1 WHERE table1.currency IS NULL
will show the relevant rows for table1.
You can do the same with table two.
This will give you two queries, that shows which rows have no couterpart.
You can then use intersect on the result, so that you have the rows that have not couterpart in either:
SELECT * FROM query1 INTERSECT SELECT * FROM query2
Now you have the list of currencies to be deleted.
You can finish this by using a subqueried delete:
DELETE FROM currencies WHERE currency IN (SELECT ...)
I have tableA with the columns ID, ColumnHeader, Value.
I'm trying to update tableB where ID, and the value in tableB.ColumnHeader with tableB.Value.
Essentially, the column headers for tableB are in a column in Table A and not column headers themselves.
I'm stuck on specifying the table name. For example, how do I run this query when I only have tablename.____ where the blank is in a column in a separate table?
update tableB set table.____ .....
As seen in the screenshot below, in Table B, 4 should become 1, and 8 should become 2, and 12 should become 3. Thanks so much.
this is a example from Northwind database:
UPDATE dbo.Products
SET dbo.Products.CategoryID = c.CategoryID
FROM Products
INNER JOIN dbo.Categories c ON dbo.Products.CategoryID = c.CategoryID
I am not getting which table and column you want to update with which table and column.
also relationship is not clear.
This doesn't make sense to me. Are you trying to update table B or A? Are there like values in table B and A that you want updated?
The basic code is as shown below:
update tableb
set column id = 'value you're updating'
where column id = 'value you're looking for' --always make this unique like a key etc.
Table A has a population of names and unique ids. Table B has the same unique ids and names. The majority of the names in table B are null, but some have an updated name. I want to merge the two tables so I get the old names from table A and new names from table B if they exist. Basically layer table B on top of table A to capture changes to the names.
I've done something like this in sas, but am having a problem in Access. merging via sas is no longer an option. can this be done in access?
You can do this in SQL using theIIFandISNULLfunctions to select the name from the correct table (from TableA if TableB is null, otherwise from TableB). If your tables has two fields:(id,the_name)a query could look like this:
SELECT a.id, IIF(ISNULL(b.the_name), a.the_name, b.the_name) AS the_name
INTO TableC
FROM TableA a
INNER JOIN TableB b ON a.id = b.id
Database: Oracle
I want to insert data from table 1 to table 2 but the catch is, primary key of table 2 is the combination of first 4 letters and last 4 numbers of the primary key of table 1.
For example:
Table 1 - primary key : abcd12349887/abcd22339887/abcder019987
In this case even if the primary key of table 1 is different, but when I extract the 1st 4 and last 4 chars, the output will be same abcd9887
So, when I use select to insert data, I get error of duplicate PK in table 2.
What I want is if the data of the PK is already present then don't add that record.
Here's my complete stored procedure:
INSERT INTO CPIPRODUCTFAMILIE
(productfamilieid, rapport, mesh, mesh_uitbreiding, productlabelid)
(SELECT DISTINCT (CONCAT(SUBSTR(p.productnummer,1,4),SUBSTR(p.productnummer,8,4)))
productnummer,
ps.rapport, ps.mesh, ps.mesh_uitbreiding, ps.productlabelid
FROM productspecificatie ps, productgroep pg,
product p left join cpiproductfamilie cpf
on (CONCAT(SUBSTR(p.productnummer,1,4),SUBSTR(p.productnummer,8,4))) = cpf.productfamilieid
WHERE p.productnummer = ps.productnummer
AND p.productgroepid = pg.productgroepid
AND cpf.productfamilieid IS NULL
AND pg.productietype = 'P'
**AND p.ROWID IN (SELECT MAX(ROWID) FROM product
GROUP BY (CONCAT(SUBSTR(productnummer,1,4),SUBSTR(productnummer,8,4))))**
AND (CONCAT(SUBSTR(p.productnummer,1,2),SUBSTR(p.productnummer,8,4))) not in
(select productfamilieid from cpiproductfamilie));
The highlighted section seems to be wrong, and because of this the data is not picking up.
Please help
Try using this.
p.productnummer IN (SELECT MAX(productnummer) FROM product
GROUP BY (CONCAT(SUBSTR(productnummer,1,4),SUBSTR(productnummer,8,4))))