对于基于表达式的索引，需要将表达式放在括号中：

CREATE INDEX matchingcol_idx  
   ON tableB USING btree ( (sub_building_name || ', ' || building_name) );

但是，如果在where子句中使用了完全相同的条件，则仅使用该索引，任何仅引用其中一列的条件都不会使用该索引。

要通过LIKE或ILIKE进行匹配，可以创建gin索引，如下所述https://niallburkley.com/blog/index-columns-for-like-in-postgres/

CREATE INDEX CONCURRENTLY idx_match_building 
   ON tableB USING gin ( (sub_building_name || ', ' || building_name) gin_trgm_ops);

验证是否已通过此查询启用扩展模块

SELECT * FROM pg_extension where extname = 'pg_trgm';
+-------+---------+----------+--------------+----------------+------------+-----------+--------------+
| oid   | extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition |
|-------+---------+----------+--------------+----------------+------------+-----------+--------------|
| 17458 | pg_trgm | 10       | 17455        | True           | 1.3        | <null>    | <null>       |
+-------+---------+----------+--------------+----------------+------------+-----------+--------------+

关于为什么concat不会削减它的相关信息：）https://www.postgresql.org/message-id/1409893231867-5817884.post%40n5.nabble.com