PostgreSQL:删除列并重新创建相关 View

Question

我创建了下面的测试表和相关 View 。

create table test_col_drp (col1 varchar(100), col2 varchar(100), col3 varchar(100));
create view test_col_drp_vw1 as select col1 col1_vw1, col2 col2_vw1, col3 col3_vw1 from test_col_drp;
create view test_col_drp_vw2 as select col1_vw1 col1_vw2, col2_vw1 col2_vw2, col3_vw1 col3_vw2 from test_col_drp_vw1;

我试图从表中删除一列，但出现以下错误:

alter table test_col_drp drop column col3;

ERROR:  cannot drop table test_col_drp column col3 because other objects depend on it
DETAIL:  view test_col_drp_vw1 depends on table test_col_drp column col3 view test_col_drp_vw2 depends on view test_col_drp_vw1
HINT:  Use DROP ... CASCADE to drop the dependent objects too.
********** Error **********

删除列并重新创建所有依赖 View 的最佳方法是什么？

致力于: x86_64-pc-mingw64 上的 PostgreSQL 9.6.6，由 gcc.exe 编译(Rev5，由 MSYS2 项目构建)4.9.2，64 位

Windows 10

Answer 1

首先，您必须删除 View 。然后，执行alter table，最后再次创建 View 。请参阅:

  -- This is what you have in your database  

 create table test_col_drp (col1 varchar(100), col2 varchar(100), col3 varchar(100));
 create view test_col_drp_vw1 as select col1 col1_vw1, col2 col2_vw1, col3 col3_vw1 from test_col_drp;
 create view test_col_drp_vw2 as select col1_vw1 col1_vw2, col2_vw1 col2_vw2, col3_vw1 col3_vw2 from test_col_drp_vw1;

-- drop views and alter table
drop view test_col_drp_vw2;
drop view test_col_drp_vw1;

alter table test_col_drp drop column col3;

-- creating the views again without col3
create view test_col_drp_vw1 as select col1 col1_vw1, col2 col2_vw1 from test_col_drp;
create view test_col_drp_vw2 as select col1_vw1 col1_vw2, col2_vw1 col2_vw2 from test_col_drp_vw1;

另一种方法是使用下降级联。在这种情况下，您不需要单独删除每个 View ，但仍然需要重新创建它们:

alter table test_col_drp drop column col3 cascade;

--  creating the views again without col3
create view test_col_drp_vw1 as select col1 col1_vw1, col2 col2_vw1 from test_col_drp;
create view test_col_drp_vw2 as select col1_vw1 col1_vw2, col2_vw1 col2_vw2 from test_col_drp_vw1;

另一个选项是创建一个 SQL 命令，使用级联和创建 View 生成更改表:

with query_result as (
    SELECT dependent_ns.nspname as dependent_schema
    , dependent_view.relname as dependent_view 
    , source_ns.nspname as source_schema
    , source_table.relname as source_table
    , pg_attribute.attname as column_name
    , row_number() over() as id
    FROM pg_depend 
    JOIN pg_rewrite ON pg_depend.objid = pg_rewrite.oid 
    JOIN pg_class as dependent_view ON pg_rewrite.ev_class = dependent_view.oid 
    JOIN pg_class as source_table ON pg_depend.refobjid = source_table.oid 
    JOIN pg_attribute ON pg_depend.refobjid = pg_attribute.attrelid 
        AND pg_depend.refobjsubid = pg_attribute.attnum 
    JOIN pg_namespace dependent_ns ON dependent_ns.oid = dependent_view.relnamespace
    JOIN pg_namespace source_ns ON source_ns.oid = source_table.relnamespace

    WHERE 1=1
    -- AND source_ns.nspname = 'public'
    AND source_table.relname like 'test_col_drp%'
    AND pg_attribute.attnum > 0 
    AND pg_attribute.attname = 'col3'
) 

select concat('alter table ', source_table, ' drop column ' , column_name, ' cascade;' ) as sql_command from query_result where id = 1
union all
select concat('create or replace view ', dependent_view, ' as select * from ', source_table, ';') as  sql_command from query_result  

然后，输出将是:

alter table test_col_drp drop column col3 cascade;
create or replace view test_col_drp_vw1 as select * from test_col_drp;
create or replace view test_col_drp_vw2 as select * from test_col_drp_vw1;