Question

有很多信息可以从postgresql中的information_schema和pg_catalog中检索到。我想检索有关由某个索引索引的列的信息，类似于我在sqlite3中使用pragma index_info(<index_name>)所实现的内容。如何在不解析create index语句的情况下实现这一目标？

Answer 1

这些东西很容易找到。

只需使用-E选项运行psql，它将显示所使用的SQL语句。因此，当运行\ d index_name时，以下语句（以及其他语句）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   a.atthasdef)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;

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（限制结果行集的能力被称为注释）：

    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         ""   '

postgresql：如何列出索引列？

2 个答案: