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Why is this? And how can I fix this?

I've checked https://dba.stackexchange.com/a/249676/106982 but n_distinct is not that far off, pg_stats says n_distinct: 623 while SELECT COUNT(*) FROM (SELECT DISTINCT function FROM "functionCall") returns 1065

Things I've tried so far:

• After reading Postgres sometimes uses inferior index for WHERE a IN (…) ORDER BY b LIMIT N I have checked n_distinct - but is not that far off, pg_stats says 623 while SELECT COUNT(*) FROM (SELECT DISTINCT function FROM "functionCall") returns 1065.

• I've increased the table SET STATISTICS to 10k and ran ANALYZE. That cuts the time in half (9s) but still won't use the index I created.

Why is this? And how can I fix this?

I've checked https://dba.stackexchange.com/a/249676/106982 but n_distinct is not that far off, pg_stats says n_distinct: 623 while SELECT COUNT(*) FROM (SELECT DISTINCT function FROM "functionCall") returns 1065