sql文件中的Postgresql命令行变量用法

Question

I am using psql command to call a file bypassing argument as -v argument=value . In the SQL file, the argument needs to be used as part of a string. For example prefix_:argument_suffix . This is not working. If I use it as prefix_:argument it works, but when it comes to the suffix it doesn't.

This is for building a database name in the create database statement.

Can somebody help with this?

Answer 1

Use another variable like:

nd@postgres=# \set argument 'aaa'
nd@postgres=# \set dbname 'foo_':argument'_bar'
nd@postgres=# select :'dbname';
┌─────────────┐
│  ?column?   │
├─────────────┤
│ foo_aaa_bar │
└─────────────┘

nd@postgres=# create database :dbname;
CREATE DATABASE

nd@postgres=# \l
                                    List of databases
┌─────────────┬──────────┬──────────┬─────────────┬─────────────┬───────────────────────┐
│    Name     │  Owner   │ Encoding │   Collate   │    Ctype    │   Access privileges   │
├─────────────┼──────────┼──────────┼─────────────┼─────────────┼───────────────────────┤
│ foo_aaa_bar │ nd       │ UTF8     │ en_US.UTF-8 │ en_US.UTF-8 │                       │
│ postgres    │ postgres │ UTF8     │ en_US.UTF-8 │ en_US.UTF-8 │                       │
│ template0   │ postgres │ UTF8     │ en_US.UTF-8 │ en_US.UTF-8 │ =c/postgres          ↵│
│             │          │          │             │             │ postgres=CTc/postgres │
│ template1   │ postgres │ UTF8     │ en_US.UTF-8 │ en_US.UTF-8 │ =c/postgres          ↵│
│             │          │          │             │             │ postgres=CTc/postgres │
└─────────────┴──────────┴──────────┴─────────────┴─────────────┴───────────────────────┘

Answer 2

The string could be built as

'prefix_' || :'variable' || '_suffix'

To use it in a CREATE DATABASE statement, you will have to use dynamic SQL in a function:

CREATE FUNCTION pg_temp.mkdb(var text) RETURNS void
   LANGUAGE plpgsql STRICT AS
$$BEGIN
   EXECUTE format('CREATE DATABASE %I;', 'prefix_' || var || '_suffix');
END;$$;

SELECT pg_temp.mkdb(:'variable');

Since the function is created in the temporary schema, it will exist only in this database session.