PostgreSQL:删除列并重新创建依赖视图

Question

我创建了下面的测试表和依赖视图。

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;

我正在尝试从表中删除一列，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视图的最佳方法是什么？

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

视窗 10

Answer 1

首先，您必须删除视图。然后，执行更改表，最后再次创建视图。看：

-- 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;

另一种方法是使用拖放级联。在这种情况下，您不需要单独删除每个视图，但仍需要重新创建它们：

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;

另一种选择是创建一个 SQL 命令，该命令使用级联和创建视图生成更改表：

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;