我试图理解为什么PostgreSQL不使用索引时，条件之一是在子查询。
我有（股票行情，日期）的索引

EXPLAIN ANALYZE SELECT OPEN 
FROM
    daily_prices dp 
WHERE
    dp.ticker = ( SELECT ticker FROM tickers_profile WHERE short_name = '1TECH' ) 
    AND DATE <= '2022-07-05'

个字符
如果子查询是内联的（作为参数）

EXPLAIN ANALYZE SELECT OPEN 
FROM
    daily_prices dp 
WHERE
    dp.ticker = '03041'
    AND DATE <= '2022-07-05'

Bitmap Heap Scan on daily_prices dp  (cost=30.42..3646.10 rows=975 width=5) (actual time=0.506..0.758 rows=285 loops=1)
  Recheck Cond: (((ticker)::text = '03041'::text) AND (date <= '2022-07-05'::date))
  Heap Blocks: exact=16
  ->  Bitmap Index Scan on daily_prices_pkey  (cost=0.00..30.18 rows=975 width=0) (actual time=0.490..0.490 rows=285 loops=1)
        Index Cond: (((ticker)::text = '03041'::text) AND (date <= '2022-07-05'::date))
Planning Time: 0.077 ms
Execution Time: 0.793 ms

的字符串
我试过：

1. CTE（带报表），性能相同
   1.连接语句，性能相同
   编辑：使用函数工作

CREATE 
    OR REPLACE FUNCTION get_ticker_from_short_name ( _short_name VARCHAR ) RETURNS TEXT AS $BODY$ SELECT
    ticker 
FROM
    tickers_profile 
WHERE
    short_name = _short_name$BODY$ LANGUAGE SQL VOLATILE COST 100

EXPLAIN ANALYZE SELECT OPEN 
FROM
    daily_prices dp 
WHERE
    dp.ticker = ( SELECT get_ticker_from_short_name ( '1TECH' ) ) 
    AND DATE <= '2022-07-05'

Bitmap Heap Scan on daily_prices dp  (cost=36.61..3969.86 rows=1065 width=5) (actual time=0.369..0.565 rows=285 loops=1)
  Recheck Cond: (((ticker)::text = $0) AND (date <= '2022-07-05'::date))
  Heap Blocks: exact=16
  InitPlan 1 (returns $0)
    ->  ProjectSet  (cost=0.00..5.27 rows=1000 width=32) (actual time=0.314..0.314 rows=1 loops=1)
          ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual time=0.000..0.001 rows=1 loops=1)
  ->  Bitmap Index Scan on daily_prices_pkey  (cost=0.00..31.08 rows=1065 width=0) (actual time=0.362..0.362 rows=285 loops=1)
        Index Cond: (((ticker)::text = $0) AND (date <= '2022-07-05'::date))
Planning Time: 0.088 ms
Execution Time: 0.604 ms