在 PostgreSQL 中编写函数时出错

Question

我已经使用这个 sn-p 代码创建了一个函数，用于在 PostgreSQL 中以 JSON 格式导出表。但是当我想使用动态路径来存储我的输出 JSON 文件作为函数的输入参数时，就会出现问题。当我用 'c:\myfile.json' 之类的东西替换 'path' 变量时，它没有任何错误。路径变量有什么问题？谢谢。

CREATE OR REPLACE FUNCTION ST_Export2JSON(tableName TEXT, fields TEXT, path TEXT)
RETURNS VOID AS 
$$
Copy(SELECT row_to_json(fc)
FROM ( SELECT 'FeatureCollection' As type, array_to_json(array_agg(f)) As     features
FROM ( SELECT 'Feature' As type, ST_AsGeoJSON(hp.geom)::json As geometry, row_to_json((select l from(select fields) as l)) As properties 
FROM tableName As hp ) As f )  As fc) to path;
$$
LANGUAGE sql IMMUTABLE STRICT

这是错误：

ERROR:  syntax error at or near "path"
LINE 7:  FROM tableName As hp ) As f )  As fc) to path;
                                              ^

Answer 1

你应该使用plpgsql dynamic command，例如：

create or replace function example(path text)
returns void language plpgsql as $$
begin
    -- instead of
    -- copy (select 1) to path;
    -- use:
    execute format('copy (select 1) to %L', path);
end $$;