PostgreSQL：如何列出索引列？

Question

从 PostgreSQL 中的 information_schema 和 pg_catalog 可以检索到大量信息。我想检索关于某个索引引用的列的信息，类似于在 sqlite3 中使用 pragma index_info(<index_name>) 实现的内容。如何在不解析 create index 语句的情况下实现这一目标？

- gruszczy

---

@OMG Ponies：因为答案并不像听起来那么简单。 - intgr

Answer 1

这些东西很容易找到。

只需使用-E选项运行psql，它就会显示所使用的SQL语句。因此，在运行\d index_name时，以下语句（等等）将用于检索索引列：

SELECT a.attname,
       pg_catalog.format_type(a.atttypid, a.atttypmod),
       (SELECT SUBSTRING(pg_catalog.pg_get_expr(d.adbin,d.adrelid) FOR 128)
        FROM pg_catalog.pg_attrdef d
        WHERE d.adrelid = a.attrelid
        AND   d.adnum = a.attnum
        AND NOT d.adisdropped),
       a.attnotnull,
       a.attnum,
       pg_catalog.pg_get_indexdef(a.attrelid, a.attnum, TRUE) AS indexdef
FROM pg_catalog.pg_attribute a
WHERE a.attrelid = (SELECT oid FROM pg_class WHERE relname = 'index_name')
AND a.attnum > 0
AND NOT a.attisdropped
ORDER BY a.attnum;

- user330315

---

我之前不知道可以用\d来显示索引信息，这个非常有帮助，还有-E选项。非常感谢。 - gruszczy

Answer 2

接受的答案对我没有用（执行时出错）。

无论如何，您可以列出数据库中的所有列，并以某种方式标记所有索引列（在注释中提到了限制结果行集的能力）：

    WITH 
    table_select as (
        select row_number() over(ORDER BY relname) as rownum, 
        c.relname, c.oid, c.reltuples
        FROM pg_class c
        JOIN pg_namespace n ON (n.oid = c.relnamespace)
        WHERE  c.relkind = 'r'::"char" 
               --AND n.nspname = '%MyNameSpaceHere%'
        ORDER BY c.relname      
    ),
    indxs as (
    select distinct t.relname as table_name, a.attname as column_name
    from pg_class t,  pg_class i, pg_index ix, pg_attribute a
    where
        t.oid = ix.indrelid
        and i.oid = ix.indexrelid
        and a.attrelid = t.oid
        and a.attnum = ANY(ix.indkey)
        and t.relkind = 'r'
        --and t.relname like 'mytable here'
        and cast (i.oid::regclass as text) like '%MyNameSpaceHere%'
    order by
        t.relname --, i.relname
    ),
    cols as (
    select a.attname, a.attrelid, c.oid, col.TABLE_NAME, col.COLUMN_NAME 
       FROM table_select c
        JOIN pg_attribute a ON (a.attrelid = c.oid) AND  (a.attname <> 'tableoid')
        LEFT JOIN information_schema.columns col ON 
(col.TABLE_NAME = c.relname AND col.COLUMN_NAME = a.attname )
      WHERE    
          ( a.attnum >= 0 ) --attnum > 0 for real columns
    )

    --select * from table_select t
    select c.TABLE_NAME, c.COLUMN_NAME, 
        case when i.column_name is not null then 'Y' else '' end as is_indexed 
    from cols c
    left join indxs i on (i.table_name = c.table_name and i.column_name = c.column_name)

示例结果：

    table_name column_name is_indexed
   'events        id          "Y"
    events       type         "Y"
    events       descr         ""   '

- xacinay