CREATE UNIQUE INDEX IF NOT EXISTS in postgreSQL - sql

Question

Plese I would like to do in PostgreSQL something like
CREATE UNIQUE INDEX IF NOT EXISTS
Any idea?

Answer 1

You can check, if an index with a given name exists with this statement.
If your index name is some_table_some_field_idx
SELECT count(*) > 0
FROM pg_class c
WHERE c.relname = 'some_table_some_field_idx'
AND c.relkind = 'i';
Starting from Postgres 9.5 you can even use
CREATE INDEX IF NOT EXISTS

Answer 2

Just another ready-to-use solution.
PostgreSQL v9.0+:
DO $BLOCK$
BEGIN
BEGIN
CREATE INDEX index_name ON table_name( column_name );
EXCEPTION
WHEN duplicate_table
THEN RAISE NOTICE 'index ''index_name '' on table_name already exists, skipping';
END;
END;
$BLOCK$;
PostgreSQL v9.5+:
CREATE INDEX IF NOT EXISTS index_name ON table_name( column_name );

Answer 3

I have wrapped a_horse_with_no_name's code with PLSQL function for more convenient usage. I hope somebody will find it useful.
CREATE OR REPLACE FUNCTION create_index(table_name text, index_name text, column_name text) RETURNS void AS $$
declare
l_count integer;
begin
select count(*)
into l_count
from pg_indexes
where schemaname = 'public'
and tablename = lower(table_name)
and indexname = lower(index_name);
if l_count = 0 then
execute 'create index ' || index_name || ' on ' || table_name || '(' || column_name || ')';
end if;
end;
$$ LANGUAGE plpgsql;
usage:
select create_index('my_table', 'my_index_name', 'id');

Answer 4

You need some procedural code for this, something like this (untested!):
do
$$
declare
l_count integer;
begin
select count(*)
into l_count
from pg_indexes
where schemaname = 'public'
and tablename = 'your_table'
and indexname = 'your_index_name';
if l_count = 0 then
execute 'create unique index public.your_index_name on public.your_table(id)';
end if;
end;
$$

Answer 5

If you are still stuck in previous versions, I would recommend not using count, but just the query directly in your if condition. Makes the code simpler. You can try something like this:
do
$$
begin
if not exists (
select indexname
from pg_indexes
where schemaname = 'schemaname'
and tablename = 'tablename'
and indexname = 'indexname'
)
then
create unique indexname (...);
end if;
end
$$;

Answer 6

Another solution that support multiple columns index, based on #Kragh answer
CREATE or replace FUNCTION create_index(_index text, _table text, VARIA
DIC param_args text[]) RETURNS void AS
$$
declare
l_count integer;
begin
select count(*) into l_count
from pg_indexes
where schemaname = 'public'
and tablename = lower(_table)
and indexname = lower(_index);
if l_count = 0 then
EXECUTE format('create index %I on %I (%s)', _index, _table, array_to_string($3,','));
end if;
END;
$$
LANGUAGE plpgsql;
and then you can use it like any other pg function:
select create_index('events_timestamp_type_idx', 'events', 'timestamp', 'type');