Question

我正在使用Postgres的元数据表（system catalogs）构建查询以获取我需要的一些信息。 pg_constraint目录中有一个名为conkey的列，其类型为int2[]，并引用pg_attribute .attnum。

我的问题不是关于系统目录本身，而是关于我如何将这个int2[]数组扩展为实际列名数组。例如：

a) pg_constraint:
conname | conrelid | conkey
const1  | 123      | {2, 3}

b) pg_class:
oid | relname
123 | table1

c) pg_attribute:
attrelid | attname | attnum
123      | colA    | 1
123      | colB    | 2
123      | colC    | 3

如何获得预期结果中的const_columns如下所示？

pseudo-query:
select b.relname as table, a.conname as constraint,
    /******> a.conkey expanded to c.attname <******/ as const_columns
    from pg_constraint a, pg_class b, pg_attribute c
    where a.conrelid = b.oid
    and c.attrelid = b.oid
    and a.conkey = c.attnum;

expected result:
table  | constraint | const_columns
table1 | const1     | {colB, colC}

Answer 1

select
    b.relname as table,
    a.conname as constraint,
    array_agg(c.attname) as const_columns
from pg_constraint a, pg_class b, pg_attribute c
where
    a.conrelid = b.oid
    and c.attrelid = b.oid
    and c.attnum in (select unnest(a.conkey))
group by b.relname, a.conname

或使用数组运算符：

    and array[c.attnum] <@ a.conkey

将数组类型列展开为引用表中的数据（元数据查询）

1 个答案: