POSTGRES Update with left outer join is not working - sql

Question

Please suggest, what am I doing wrong.
UPDATE uc
SET uc.selected_value_id = cv.id, uc.fixed_value = NULL
FROM unit_characteristic uc
left JOIN characteristic_value cv ON uc.fixed_value like CONCAT(cv.value,'%')
WHERE cv.characteristic_id = 6
and uc.characteristic_id = 6
and uc.unit_id in (6313,6314)
Getting error
SQL Error [42P01]: ERROR: relation "uc" does not exist
Position: 8
org.postgresql.util.PSQLException: ERROR: relation "uc" does not exist
Position: 8
While this select is working fine
select count(uc.*)
FROM unit_characteristic uc
left JOIN characteristic_value cv ON uc.fixed_value like CONCAT(cv.value,'%')
WHERE cv.characteristic_id = 6
and uc.characteristic_id = 6
and uc.unit_id in (6313,6314)

Answer 1

you don't have to repeat the target table in the FROM clause; it is already in the range table
the target table can have an alias
but, the SET columnname = new_value line must not use this alias. It is implicit (since there is only one table reference to be updated)
UPDATE unit_characteristic uc
SET selected_value_id = cv.id
, fixed_value = NULL
FROM characteristic_value cv
WHERE uc.fixed_value like cv.value || '%'
AND cv.characteristic_id = 6
AND uc.characteristic_id = 6
AND uc.unit_id in (6313, 6314)
;

Answer 2

In Postgres, the reference in the update cannot refer to a table in the from. I suspect you want:
update unit_characteristic uc
set selected_value_id = cv.id,
fixed_value = NULL
from characteristic_value cv
where uc.fixed_value like cv.value || '%' and
cv.characteristic_id = 6 and
uc.characteristic_id = 6 and
uc.unit_id in (6313, 6314);
Note that your version of the query uses left join. But the where clause turns that into an inner join anway.