从 SQL DDL 语句的现有表中过滤列名称

Question

Is it possible to filter on column names themselves in psql? I want to generate a limited version of the original table (with several hundred columns) in a separate schema a la (pseudocode):

create table why.am_i_doing_this
    select *
    from original.table 
    where column_name_of_the_table not in ('column_1', 'column_2' );

Answer 1

Build the DDL command dynamically. You can do it in two steps:

1. Build statement:

    SELECT 'CREATE TABLE why.am_i_doing_this AS SELECT ' || string_agg(column_name, ', ' ORDER BY ordinal_position) || ' FROM original.table' FROM information_schema.columns WHERE table_schema = 'original' AND table_name = 'table' AND column_name NOT IN ('column_1', 'column_2');

2. (Check it's good.) Then execute the generated statement in a second round trip to the server.

This is based on the information schema viewinformation_schema.columns . Alternatively, you could use pg_catalog.pg_attribute . Related:

• How to check if a table exists in a given schema

But it can be done in a single round trip to the server, too:

With a DO statement from any client

DO is just a simple wrapper for ad-hoc execution of PL/pgSQL code. You might do the same in a function or procedure.

DO
$$
BEGIN
   EXECUTE (
   SELECT 'CREATE TABLE why.am_i_doing_this AS SELECT '
       || string_agg(column_name, ', ' ORDER BY ordinal_position)
       || ' FROM original.table'
   FROM   information_schema.columns
   WHERE  table_schema = 'original'
   AND    table_name = 'table'
   AND    column_name NOT IN ('column_1', 'column_2')
   );
END
$$;

Simpler with psql meta-command \gexec

Since you mentioned the default interactive terminal psql . There you can use \gexec . It...

Sends the current query buffer to the server, then treats each column of each row of the query's output (if any) as a SQL statement to be executed.

So:

SELECT 'CREATE TABLE why.am_i_doing_this AS SELECT '
    || string_agg(column_name, ', ' ORDER BY ordinal_position)
    || ' FROM original.table'
FROM   information_schema.columns
WHERE  table_schema = 'original'
AND    table_name = 'table'
AND    column_name NOT IN ('column_1', 'column_2')\gexec