Functional Index LOWER PostgreSQL not working

The below SQL query runs in 2s: SELECT * FROM fb_name INNER JOIN fb_kg ON mid = subject_mid WHERE LOWER(alias) = LOWER('Polaski') AND fb_kg.relation = 'location/location/containedby' The below SQL query runs in 2ms: SELECT * FROM fb_name INNER JOIN fb_kg ON mid = subject_mid WHERE alias = 'Polaski' AND fb_kg.relation = 'location/location/containedby' The difference between the two queries is the inclusion of the LOWER function. There has been an index created for both queries: CREATE INDEX fb_name_lower_alias ON fb_name (lower(alias)); CREATE INDEX fb_name_mid_lower_alias_index ON fb_name (mid, lower(alias)); CREATE INDEX fb_name_alias ON fb_name (alias); CREATE INDEX fb_name_mid_alias_index ON fb_name (mid, alias); EXPLAIN for LOWER: "Gather (cost=247515.73..249133.22 rows=5708 width=70)" " Workers Planned: 2" " -> Merge Join (cost=246515.73..247562.42 rows=2378 width=70)" " Merge Cond: ((fb_kg.subject_mid)::text = (fb_name.mid)::text)" " -> Sort (cost=205352.30..205794.73 rows=176972 width=44)" " Sort Key: fb_kg.subject_mid" " -> Parallel Bitmap Heap Scan on fb_kg (cost=14116.24..184480.39 rows=176972 width=44)" " Recheck Cond: ((relation)::text = 'location/location/containedby'::text)" " -> Bitmap Index Scan on relation_index (cost=0.00..14010.06 rows=424733 width=0)" " Index Cond: ((relation)::text = 'location/location/containedby'::text)" " -> Sort (cost=41163.43..41232.45 rows=27611 width=26)" " Sort Key: fb_name.mid" " -> Bitmap Heap Scan on fb_name (cost=750.54..39126.71 rows=27611 width=26)" " Recheck Cond: (lower((alias)::text) = 'polaski'::text)" " -> Bitmap Index Scan on fb_name_lower_alias_varchar_pattern_ops (cost=0.00..743.64 rows=27611 width=0)" " Index Cond: (lower((alias)::text) = 'polaski'::text)" Other EXPLAIN: "Nested Loop (cost=11.45..13502.52 rows=2 width=70)" " -> Bitmap Heap Scan on fb_name (cost=4.64..48.23 rows=11 width=26)" " Recheck Cond: ((alias)::text = 'Polaski'::text)" " -> Bitmap Index Scan on fb_name_alias_index (cost=0.00..4.64 rows=11 width=0)" " Index Cond: ((alias)::text = 'Polaski'::text)" " -> Bitmap Heap Scan on fb_kg (cost=6.81..1223.04 rows=8 width=44)" " Recheck Cond: ((subject_mid)::text = (fb_name.mid)::text)" " Filter: ((relation)::text = 'location/location/containedby'::text)" " -> Bitmap Index Scan on subject_mid_index (cost=0.00..6.81 rows=316 width=0)" " Index Cond: ((subject_mid)::text = (fb_name.mid)::text)" CREATE TABLE definitions CREATE TABLE fb_kg (object_mid varchar NOT NULL, relation varchar NOT NULL, subject_mid varchar NOT NULL, PRIMARY KEY(object_mid, relation, subject_mid)); CREATE TABLE fb_name (mid varchar NOT NULL, alias varchar NOT NULL, PRIMARY KEY(mid, alias)); How come with the same indexes the LOWER function is about 60x slower?