Postgresql 一对多如何将原本用,隔开的id替换为name

数据格式：

id     pid
1    1,2,3
2    2,5

将pid替换为name

SELECT projectId, string_agg(name, ',') FROM 
(select id projectId,unnest(regexp_split_to_array(pid, ',')) buyBackId from a project) L 
LEFT JOIN  buyBack 
ON L.buyBackId=buyBack.id GROUP BY projectId