生成SQL以更新主键

Question

我想更改主键和引用此值的所有表行.

# table master
master_id|name
===============
foo|bar

# table detail
detail_id|master_id|name
========================
1234|foo|blu

如果我给出一个脚本或功能

 table=master, value-old=foo, value-new=abc

我想创建一个SQL片段,在所有引用表"master"的表上执行更新:

update detail set master_id=value-new where master_id=value-new;
.....

在内省的帮助下,这应该是可能的.

我用postgres.

更新

问题是,有许多表具有表"master"的外键.我想要一种方法来自动更新所有具有外键到主表的表.

Answer 1

到目前为止,处理主键更改的最简单方法是ALTER引用外键约束ON UPDATE CASCADE.

然后,您可以自由更新主键值,更改将级联到子表.由于所有随机I/O,它可能是一个非常缓慢的过程,但它会起作用.

您需要注意在此过程中不要违反主键列的唯一性约束.

更简单但更快捷的方法是UNIQUE为新PK添加新列,填充它,向指向新PK的所有引用表添加新列,删除旧FK约束和列,然后最终删除旧PK.

Answer 2

如果您需要更改PK，可以使用DEFFERED CONSTRAINTS：

SET CONSTRAINTS设置当前事务中的约束检查行为。在每个语句的末尾检查IMMEDIATE约束。在提交事务之前，不检查DEFERRED约束。每个约束都有其自己的立即或延迟模式。

数据准备：

CREATE TABLE master(master_id VARCHAR(10) PRIMARY KEY, name VARCHAR(10));
INSERT INTO master(master_id, name) VALUES ('foo', 'bar');

CREATE TABLE detail(detail_id INT PRIMARY KEY, master_id VARCHAR(10)
   ,name VARCHAR(10)
   ,CONSTRAINT  fk_det_mas FOREIGN KEY (master_id) REFERENCES master(master_id));

INSERT INTO detail(detail_id, master_id, name) VALUES (1234,'foo','blu');

在正常情况下，如果您尝试更改母版详细信息，则会导致错误：

update detail set master_id='foo2' where master_id='foo';
-- ERROR:  insert or update on table "detail" violates foreign key 
-- constraint "fk_det_mas"
-- DETAIL:  Key (master_id)=(foo2) is not present in table "master"

update master set master_id='foo2' where master_id='foo';
-- ERROR:  update or delete on table "master" violates foreign key
-- constraint "fk_det_mas" on table "detail"
-- DETAIL:  Key (master_id)=(foo) is still referenced from table "detail".

但是，如果将FK分辨率更改为递减，则没有问题：

ALTER TABLE detail DROP CONSTRAINT fk_det_mas ;
ALTER TABLE detail ADD CONSTRAINT fk_det_mas FOREIGN KEY (master_id) 
REFERENCES master(master_id) DEFERRABLE;

BEGIN TRANSACTION;
SET CONSTRAINTS ALL DEFERRED;
UPDATE master set master_id='foo2' where master_id = 'foo';
UPDATE detail set master_id='foo2' where master_id = 'foo';
COMMIT;

DBFiddle演示

请注意，您可以在事务内做很多事情，但是在COMMIT 所有引用完整性检查期间都必须进行。

编辑

如果要自动执行此过程，可以使用动态SQL和元数据表。这里是FK专栏的概念证明：

CREATE TABLE master(master_id VARCHAR(10) PRIMARY KEY, name VARCHAR(10));
INSERT INTO master(master_id, name)
VALUES ('foo', 'bar');

CREATE TABLE detail(detail_id INT PRIMARY KEY, master_id VARCHAR(10),
   name VARCHAR(10)
  ,CONSTRAINT  fk_det_mas FOREIGN KEY (master_id) 
   REFERENCES master(master_id)DEFERRABLE ) ;
INSERT INTO detail(detail_id, master_id, name) VALUES (1234,'foo','blu');

CREATE TABLE detail_second(detail_id INT PRIMARY KEY, name VARCHAR(10),
   master_id_second_name VARCHAR(10)
  ,CONSTRAINT  fk_det_mas_2 FOREIGN KEY (master_id_second_name) 
   REFERENCES master(master_id)DEFERRABLE ) ;
INSERT INTO detail_second(detail_id, master_id_second_name, name) 
VALUES (1234,'foo','blu');

和代码：

BEGIN TRANSACTION;
SET CONSTRAINTS ALL DEFERRED;
DO $$
DECLARE
   old_pk TEXT = 'foo';
   new_pk TEXT = 'foo2';
   table_name TEXT = 'master';
BEGIN
-- update childs
EXECUTE (select 
         string_agg(FORMAT('UPDATE %s SET %s = ''%s'' WHERE %s =''%s'' ;'
            ,c.relname,pa.attname, new_pk,pa.attname, old_pk),CHR(13)) AS sql
         from  pg_constraint pc
         join pg_class c on pc.conrelid = c.oid
         join pg_attribute pa ON pc.conkey[1] = pa.attnum 
          and pa.attrelid = pc.conrelid
         join pg_attribute pa2 ON pc.confkey[1] = pa2.attnum 
          and pa2.attrelid = table_name::regclass
         where pc.contype = 'f');

-- update parent        
EXECUTE ( SELECT FORMAT('UPDATE %s SET %s = ''%s'' WHERE %s =''%s'';'
         ,c.relname,pa.attname, new_pk,pa.attname, old_pk)
 FROM pg_constraint pc
 join pg_class c on pc.conrelid = c.oid
 join pg_attribute pa ON pc.conkey[1] = pa.attnum 
  and pa.attrelid = pc.conrelid
 WHERE pc.contype IN ('p','u')
   AND conrelid = table_name::regclass
);       

END
$$;
COMMIT;

DBFiddle演示2

编辑2：

我试过了，但是没有用。如果脚本可以显示SQL，那就太好了。这就够了。查看生成的SQL之后，如果psql -f我可以执行它

你试过了吗？它对我不起作用。

是的，我已经尝试过了。只需查看上面的实时演示链接。我准备了具有更多调试信息的相同演示：

• 之前的值
• 执行的SQL
• 之后的值

请确保将FK定义为DEFFERED。

具有调试信息的DBFiddle 2

最后编辑

然后，我想查看sql而不是执行它。我从您的小提琴中删除了“表演”，但随后出现错误。参见：http : //dbfiddle.uk/?rdbms=postgres_10&fiddle=b9431c8608e54b4c42b5dbd145aa1458

如果只想获取SQL代码，则可以创建函数：

CREATE FUNCTION generate_update_sql(table_name VARCHAR(100), old_pk VARCHAR(100), new_pk VARCHAR(100))
RETURNS TEXT 
AS 
$$
BEGIN
RETURN 
-- update childs
(SELECT 
         string_agg(FORMAT('UPDATE %s SET %s = ''%s'' WHERE %s =''%s'' ;',  c.relname,pa.attname, new_pk,pa.attname, old_pk),CHR(13)) AS sql
         FROM  pg_constraint pc
         JOIN pg_class c on pc.conrelid = c.oid
         JOIN pg_attribute pa ON pc.conkey[1] = pa.attnum and pa.attrelid = pc.conrelid
         JOIN pg_attribute pa2 ON pc.confkey[1] = pa2.attnum and pa2.attrelid = table_name::regclass
         WHERE pc.contype = 'f') || CHR(13) ||
-- update parent        
(SELECT FORMAT('UPDATE %s SET %s = ''%s'' WHERE %s =''%s'';',  c.relname,pa.attname, new_pk,pa.attname, old_pk)
 FROM pg_constraint pc
 JOIN pg_class c on pc.conrelid = c.oid
 JOIN pg_attribute pa ON pc.conkey[1] = pa.attnum and pa.attrelid = pc.conrelid
 WHERE pc.contype IN ('p','u')
   AND conrelid = table_name::regclass)
;       
END
$$ LANGUAGE  plpgsql;

并执行：

SELECT generate_update_sql('master', 'foo', 'foo');

UPDATE detail SET master_id = 'foo' WHERE master_id ='foo' ;
UPDATE detail_second SET master_id_second_name = 'foo' 
 WHERE master_id_second_name ='foo' ; 
UPDATE master SET master_id = 'foo' WHERE master_id ='foo';

DBFiddle功能演示

当然，还有改进的地方，例如处理诸如“名称中有空格的表”之类的标识符，等等。