Case, Select and Update in a single query - sql

Question

I am trying to do the following, but I get an error on DELETE FROM, any idea why? So how can I check if the createts=endts in person_net_contacts is true for certain persondID then Delete... else Update...
SELECT
createts, endts,
CASE WHEN createts = endts
THEN DELETE FROM person_net_contacts where personid='276178';
ELSE UPDATE person_net_contacts SET endts = current_timestamp
WHERE personid='276178';
FROM person_net_contacts

Answer 1

You can do this with a single query if you use writeable CTEs:
with to_check as (
SELECT personid, createts, endts, createts = endts as delete_this
WHERE personid = '276178'
FROM person_net_contacts
), deleted as (
delete from person_net_contacts
where personid = (select personid
from to_check
where delete_this)
)
update person_net_contacts pnc
SET endts = current_timestamp
from to_check tc
where tc.personid = pnc.personid
and not tc.delete_this;
The first CTE selects the row from the table and creates a flag that tells us if the row should be deleted or not. The second CTE then deletes rows based on that flag and the final statement updates the row if needed.
This also works for multiple rows assuming that personid is unique.
You should also compare numbers to numbers '276178' is a string value, not a number. If personid is defined as a number data type (integer, bigint or something similar) you should use where personid = 276178. Never put single quotes around numbers.

Answer 2

You can delete or update a row in one query using with statement, e.g.:
with delete_person as (
delete from person_net_contacts
where personid = '276178'
and createts = endts
returning 'deleted'::text, createts, endts
),
update_person as (
update person_net_contacts
set endts = current_timestamp
where personid = '276178'
and createts is distinct from endts
returning 'updated'::text, createts, endts
)
select *
from delete_person
union all
select *
from update_person;

Answer 3

You can't mix SELECT, DELETE, UPDATE, CASE like this. I assume you want to do this:
DELETE FROM person_net_contacts
WHERE personid='276178' AND createts=endts;
UPDATE person_net_contacts
SET endts = current_timestamp
WHERE personid='276178' AND createts!=endts;
-- the last condition only kicks in if you run the two statements in a different order

Answer 4

This mix of operations (SELECT and DELETE, UPDATE) are not part of a SQL expression. However you can run a SELECT, DELETE and UPDATE operations independently using the right conditions:
All the select fields must be an expression that returns some value: UPDATE or DELETE operations are not intended for that.
SELECT createts, endts
FROM person_net_contacts
WHERE personid='276178';
Delete the record when createts = endts
DELETE FROM person_net_contacts where personid='276178' and createts = endts;
Update the record when createts <> endts (the last condition can be ommited , the update only affects records that are not deleted in the previous command)
UPDATE person_net_contacts SET endts = current_timestamp where personid='276178' and createts <> endts;

Answer 5

IF EXISTS(SELECT 1 FROM person_net_contacts WHERE personid='276178' AND DATEDIFF(DAY,createts,endts) = 0)
BEGIN
DELETE FROM person_net_contacts where personid='276178'
END
ELSE
BEGIN
UPDATE person_net_contacts SET endts = current_timestamp where personid='276178'
END