So I have a table in SQL server that is defined as such
create table test(value varchar(200), Reverse(value) as valueReverse);
now when I insert something in this table lets say I insert the string hello, it will store the value in the table as such.
value | valueReverse
--------------------
hello | olleh
I am trying to convert the table into PostgreSQL however the reverse() function is not working and it's giving me errors. What is the correct way to create this table in postgres?
For PostgreSQL 12 and above
If you are using Postgres 12 or higher then you can use GENERATED ALWAYS AS for the column valueReverse like below: Manual
create table test(value varchar(200),
valueReverse varchar(200) generated always as (reverse(value)) STORED );
For PostgreSQL 11 or below
For earlier version you can use Triggers like below.
Creating Trigger Function
create or replace function trig_reverse() returns trigger as
$$
begin
new.valueReverse=reverse(new.value);
return new;
end;
$$
language plpgsql
Creating Trigger
create trigger trig_rev
before insert or update on test
for each row
execute procedure trig_reverse();
Do not store string twice (redundantly). It will be much cleaner and cheaper overall to store it once and produce the reverted copy on the fly. You can use a VIEW if you need a drop-in replacement for your table:
CREATE TABLE base_test(value varchar(200));
INSERT INTO base_test VALUES ('hello');
CREATE VIEW test AS
SELECT *, reverse(value) AS value_reverse
FROM base_test;
db<>fiddle here
Related: