Subquery not using Index, even if forcing

Using MariaDB 10.5.12 on CentOS 7 If it makes any difference, my "optimizer_use_condition_selectivity" = 1 If I run: EXPLAIN SELECT COUNT(*) FROM ips WHERE ip="1.2.3.4" This query uses the index on the ip column (simple index). However, if I run (simplest example query I could get): EXPLAIN SELECT srl.id, (SELECT COUNT(*) FROM ips WHERE ip=srl.ip) as ipcount FROM srl LIMIT 10 The subquery on the ips table doesn't have ip as possible_keys, it uses the time index (which isn't even used in the query!), and does a table scan (and this is a huge table). If I put FORCE INDEX(ip), the EXPLAIN says it uses the ip key, but it still does a table scan. If I hardcode an IP, like: EXPLAIN SELECT srl.id, (SELECT COUNT(*) FROM ips WHERE ip="1.2.3.4") as ipcount FROM srl LIMIT 10 It uses the ip key as intended. **What is preventing the subquery from using the index as supposed, in the ip=srl.ip example?** ANALYZE FORMAT=JSON: { "query_block": { "select_id": 1, "r_loops": 1, "r_total_time_ms": 19537.7025, "table": { "table_name": "srl", "access_type": "ALL", "r_loops": 1, "rows": 92181, "r_rows": 10, "r_table_time_ms": 0.055588922, "r_other_time_ms": 0.116198584, "filtered": 100, "r_filtered": 100 }, "subqueries": [ { "expression_cache": { "r_loops": 10, "r_hit_ratio": 30, "query_block": { "select_id": 2, "r_loops": 7, "r_total_time_ms": 19537.40246, "table": { "table_name": "ips", "access_type": "index", "key": "time", "key_length": "4", "used_key_parts": ["time"], "r_loops": 7, "rows": 4948857, "r_rows": 5949193, "r_table_time_ms": 12379.15752, "r_other_time_ms": 7158.182676, "filtered": 100, "r_filtered": 1.656887e-4, "attached_condition": "convert(ips.ip using utf8mb4) = srl.ip", "using_index": true } } } } ] } }