Question

我正在使用PostgreSQL 10.4，并且有2个表：

人：

select distinct a from tbl;
select distinct b from tbl;
select distinct c from tbl;
select distinct d from tbl;

国家/地区：

CREATE TABLE person (
  nationality character varying(100),
  name character varying(100),
  age integer
);

这是我要运行的查询：

CREATE TABLE country (
  demonym character varying(50),
  name character varying(50)
);

这会产生错误：

错误：json类型的输入语法无效

第11行：WHERE'nationalitiesCount':: json->'1'> 10

详细信息：令牌“ nationalitiesCount”无效。

上下文：JSON数据，第1行：nationalitiesCount

第二行的第一行select "c"."name", (SELECT row_to_json(r) FROM ( SELECT COALESCE(sum(CASE WHEN p."nationality"='finn' THEN 1 ELSE 0 END),0) as "1", COALESCE(sum(CASE WHEN p."nationality"='spanish' THEN 1 ELSE 0 END),0) as "2" FROM "person" as p WHERE "p"."nationality"="c"."demonym" ) as r) as "nationalitiesCount" from "country" as c WHERE 'nationalitiesCount'::json->'1' > 10高亮显示为导致错误出现的代码。

问题：如何纠正错误？

Answer 1

第一个问题是，对列的引用不应该用单引号引起来，尽管它们可以/有时必须用双引号引起，这就是为什么它不喜欢'nationalitiesCount':: json->'1' 。第二个原因是，列名nationalitiesCount是在查询的SELECT部分中定义的，并且不能在定义它的查询的WHERE子句中引用，因此您可以将查询移到子查询中，以便在外部进行引用子查询。

select *
from (select "c"."name",
    (SELECT row_to_json(r) 
     FROM (
      SELECT
       COALESCE(sum(CASE WHEN p."nationality"='finn' THEN 1 ELSE 0 END),0) as "1",
       COALESCE(sum(CASE WHEN p."nationality"='spanish' THEN 1 ELSE 0 END),0) as "2"

       FROM "person" as p
       WHERE "p"."nationality"="c"."demonym"
     ) as r) as "nationalitiesCount"
from "country" as c 
) t
WHERE (t."nationalitiesCount"->>'1')::integer > 10

错误：JSON类型的输入语法无效

1 个答案: