如何找到通過外鍵引用特定行的表？

Question

給定這樣的結構：

CREATE TABLE reference_table (
  reference_table_key numeric NOT NULL,
  reference_value numeric,
  CONSTRAINT reference_table_pk PRIMARY KEY (reference_table_key)
);

CREATE TABLE other_table (
  other_table_key numeric NOT NULL,
  reference_table_key numeric,
  CONSTRAINT other_table_pk PRIMARY KEY (other_table_key),
  ONSTRAINT other_table_reference_fk FOREIGN KEY (reference_table_key)
      REFERENCES reference_table (reference_table_key) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE SET NULL
);

CREATE TABLE another_table (
  another_table_key numeric NOT NULL,
  do_stuff_key numeric,
  CONSTRAINT another_table_pk PRIMARY KEY (another_table_key),
  ONSTRAINT another_table_reference_fk FOREIGN KEY (do_stuff_key)
      REFERENCES reference_table (reference_table_key) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE SET NULL
);

--there are 50-60 tables which have similar foreign key references to reference_table

我想編寫一個查詢，告訴我other_table和another_table中的主鍵以及reference_value為NULL的更多表。

在偽代碼中：

SELECT table_name, table_primary_key, table_fk_column_name
FROM ?????? some PG table ???????, reference_table
WHERE reference_table.reference_value IS NULL;

結果如下所示：

table_name | table_primary_key | table_fk_column_name | reference_table_pk
---------------------------------------------------------------------------
other_table   | 2                |  reference_table_key | 7
other_table   | 4                |  reference_table_key | 56
other_table   | 45               |  reference_table_key | 454
other_table   | 65765            |  reference_table_key | 987987
other_table   | 11               |  reference_table_key | 3213
another_table | 3                |  do_stuff_key        | 4645
another_table | 5                |  do_stuff_key        | 43546
another_table | 7                |  do_stuff_key        | 464356
unknown_table | 1                |  unkown_column_key   | 435435
unknown_table | 1                |  some_other_column_key | 34543
unknown_table | 3                |  unkown_column_key   | 124
unknown_table | 3                |  some_other_column_key | 123

這類似於但不是Postgres的重復：SQL列出表外鍵 。 這個問題說明了表的結構。 我想找到特定的實例。

本質上，如果我DELETE FROM reference_table WHERE reference_value IS NULL; ，Postgres的有做一些內部找出它需要一套reference_table_key在第2行中other_table為NULL。 我想看看這些行是什么。

有查詢可以做到這一點嗎？ 有沒有可以傳遞給DELETE調用的修飾符，可以告訴我該DELETE將影響哪些表/行/列？

Answer 1

引用列中的NULL值

此查詢生成DML語句以查找所有表中的所有行 ，其中一列具有引用另一個表的外鍵約束，但在該列中保留NULL值：

WITH x AS (
 SELECT c.conrelid::regclass    AS tbl
      , c.confrelid::regclass   AS ftbl
      , quote_ident(k.attname)  AS fk
      , quote_ident(pf.attname) AS pk
 FROM   pg_constraint c
 JOIN   pg_attribute  k ON (k.attrelid, k.attnum) = (c.conrelid, c.conkey[1])
 JOIN   pg_attribute  f ON (f.attrelid, f.attnum) = (c.confrelid, c.confkey[1])
 LEFT   JOIN pg_constraint p  ON p.conrelid = c.conrelid AND p.contype = 'p'
 LEFT   JOIN pg_attribute  pf ON (pf.attrelid, pf.attnum)
                               = (p.conrelid, p.conkey[1])
 WHERE  c.contype   = 'f'
 AND    c.confrelid = 'fk_tbl'::regclass  -- references to this tbl
 AND    f.attname   = 'fk_tbl_id'         -- and only to this column
)
SELECT string_agg(format(
'SELECT %L AS tbl
     , %L AS pk
     , %s::text AS pk_val
     , %L AS fk
     , %L AS ftbl
FROM   %1$s WHERE %4$s IS NULL'
                  , tbl
                  , COALESCE(pk 'NONE')
                  , COALESCE(pk 'NULL')
                  , fk
                  , ftbl), '
UNION ALL
') || ';'
FROM   x;

產生這樣的查詢：

SELECT 'some_tbl' AS tbl
     , 'some_tbl_id' AS pk
     , some_tbl_id::text AS pk_val
     , 'fk_tbl_id' AS fk
     , 'fk_tbl' AS ftbl
FROM   some_tbl WHERE fk_tbl_id IS NULL
UNION ALL
SELECT 'other_tbl' AS tbl
     , 'other_tbl_id' AS pk
     , other_tbl_id::text AS pk_val
     , 'some_name_id' AS fk
     , 'fk_tbl' AS ftbl
FROM   other_tbl WHERE some_name_id IS NULL;

產生如下輸出：

    tbl    |     pk       | pk_val |    fk        |  ftbl
-----------+--------------+--------+--------------+--------
 some_tbl  | some_tbl_id  | 49     | fk_tbl_id    | fk_tbl
 some_tbl  | some_tbl_id  | 58     | fk_tbl_id    | fk_tbl
 other_tbl | other_tbl_id | 66     | some_name_id | fk_tbl
 other_tbl | other_tbl_id | 67     | some_name_id | fk_tbl

• 不能可靠地覆蓋多列外鍵或主鍵 。 您必須為此使查詢更復雜。

• 我投所有的主鍵值 text涵蓋所有類型。

• 調整或刪除這些行，以找到指向另一個或任何列/表的外鍵：

   AND c.confrelid = 'fk_tbl'::regclass AND f.attname = 'fk_tbl_id' -- and only this column 

• 已在PostgreSQL 9.1.4中測試。 我使用pg_catalog表。 實際上，我在這里使用的所有內容都不會改變，但這在主要版本中不能保證。 如果您需要它在更新中可靠地工作，請使用information_schema表重寫它。 那比較慢，但是可以肯定。

• 我沒有在生成的DML腳本中quote_ident()表名，因為quote_ident()會因架構限定名而失敗。 您有責任避免使用有害的表名，例如"users; DELETE * FROM users;" 。 花費更多的精力，您可以分別檢索架構名稱和表名稱，並使用quote_ident() 。

---

引用列中的NULL值

我的第一個解決方案與您的要求有一些細微的差別，因為您所描述的（根據我的理解）不存在。 值NULL為“未知”，無法引用。 如果你真的想找到一個行NULL在具有FK約束指向它（不特定的行與列值NULL值，當然），那么查詢可以大大簡化：

WITH x AS (
 SELECT c.confrelid::regclass   AS ftbl
       ,quote_ident(f.attname)  AS fk
       ,quote_ident(pf.attname) AS pk
       ,string_agg(c.conrelid::regclass::text, ', ') AS referencing_tbls
 FROM   pg_constraint c
 JOIN   pg_attribute  f ON (f.attrelid, f.attnum) = (c.confrelid, c.confkey[1])
 LEFT   JOIN pg_constraint p  ON p.conrelid = c.confrelid AND p.contype = 'p'
 LEFT   JOIN pg_attribute  pf ON (pf.attrelid, pf.attnum)
                               = (p.conrelid, p.conkey[1])
 WHERE  c.contype = 'f'
 -- AND    c.confrelid = 'fk_tbl'::regclass  -- only referring this tbl
 GROUP  BY 1, 2, 3
)
SELECT string_agg(format(
'SELECT %L AS ftbl
     , %L AS pk
     , %s::text AS pk_val
     , %L AS fk
     , %L AS referencing_tbls
FROM   %1$s WHERE %4$s IS NULL'
                  , ftbl
                  , COALESCE(pk, 'NONE')
                  , COALESCE(pk, 'NULL')
                  , fk
                  , referencing_tbls), '
UNION ALL
') || ';'
FROM   x;

在整個數據庫中查找所有此類行（注釋了對一個表的限制）。 經過Postgres 9.1.4測試並為我工作。

我將多個引用同一外來列的表分組到一個查詢中，並添加了一個引用表列表以進行概述。

Answer 2

您需要此查詢的聯合：

select *
from ((select 'other_table' as table_name,
               other_table_key as primary_key,
               'reference_table_key' as table_fk,
               ot.reference_table_key
       from other_table ot left outer join
            reference_table rt
            on ot.reference_table_key = rt.reference_table_key
       where rt.reference_value is null
      ) union all
      (select 'another_table' as table_name,
               another_table_key as primary_key,
               'do_stuff_key' as table_fk,
               at.do_stuff_key
       from another_table at left outer join
            reference_table rt
            on at.do_stuff_key = rt.reference_table_key
       where rt.reference_value is null
      )
     ) t