如何找到通过外键引用特定行的表？

小编典典

如何找到通过外键引用特定行的表？

sql

给定这样的结构：

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

我想写一个查询，告诉我other_table和another_table中的主键以及reference_value为NULL的更多表。

在伪代码中：

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

结果将类似于：

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

这类似于但不是Postgres：SQL列出表外键的副本。这个问题说明了表的结构。我想找到特定的实例。

本质上，如果我愿意的话DELETE FROM reference_table WHERE reference_value IS NULL;，postgres必须在内部做一些事情以弄清楚它需要将reference_table_key第2行设置other_table为NULL。我想看看这些行将是什么。

有查询可以做到这一点吗？有没有可以传递给DELETE调用的修饰符，该修饰符可以告诉我该DELETE将影响哪些表/行/列？

阅读 165

2021-03-17

共1个答案

小编典典

引用列中的NULL值

该查询生成DML语句以查找所有表中的 所有行 ，其中一列具有 引用另一个表 但NULL在该列中保留值的外键约束：

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;

产生这样的查询：

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;

产生如下输出：

    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

不能可靠地覆盖多列外键或主键 。您必须为此使查询更复杂。
我投所有主键的值，以text涵盖所有类型。
调整或删除这些行，以找到指向另一个或任何列/表的外键：
```
AND    c.confrelid = 'fk_tbl'::regclass
```
AND f.attname = ‘fk_tbl_id’ – and only this column
已在PostgreSQL 9.1.4中测试。我用pg_catalog桌子。实际上，我在这里使用的所有内容都不会改变，但是在主要版本中不能保证这一点。information_schema如果您需要它在更新之间可靠地工作，请使用表格将其重写。那比较慢，但是可以肯定。
我没有在生成的DML脚本中清除表名，因为quote_ident()使用模式限定名将失败。避免使用有害的表名是您的责任"users; DELETE * FROM users;"。付出更多的努力，您可以分别检索schema-name和table name并使用quote_ident()。

引用列中的NULL值

我的第一个解决方案与您的要求有一些细微的差别，因为您所描述的（根据我的理解）不存在。该值NULL是“未知”，无法引用。如果你真的想找到一个排NULL在具有FK约束指着一列值
到它（不特定行与NULL价值，当然），那么查询可以大大简化：

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;

查找整个数据库中的所有此类行（注释了对一个表的限制）。经过Postgres 9.1.4的测试，可以为我工作。

我将多个引用同一外来列的表归为一个查询，并添加了一个引用表列表以进行概述。

2021-03-17