Variable for Database Link Name

问题

I want to do v$session@remotedatabase where remotedatabase is a variable for a dblink address. Is that possible?

I'm using Apex 4 and trying to get temporary space on all databases.

Current query

select 'Total temp space available in :Database is '||sum(bytes)/1024/1024 ||' mb' from v$tempfile@:Database

yeilds ORA-01729: database link name expected because the variable isn't resolved correcltly?

I'm quite new to SQL, sorry

回答1:

You would need to use dynamic SQL in order to have the database link be variable. In PL/SQL, that would look something like

DECLARE
  l_sql_stmt varchar2(1000);
  l_tmp_space varchar2(1000);
  l_database  varchar2(100) := <<db link name>>;
BEGIN
  l_sql_stmt := 'select ''Total temp space available in ' ||l_database  || ' is '' || sum(bytes)/1024/1024 ||'' mb'' from v$tempfile@' || l_database;
  dbms_output.put_line( l_sql_stmt );
  EXECUTE IMMEDIATE l_sql_stmt
    INTO l_tmp_space;
  dbms_output.put_line( l_tmp_space );
END;

Basically, you need to construct a string that contains the SQL statement and then execute that dynamically generated string (that's more complicated when the SQL statement itself is building up a string as yours is here-- that makes figuring out which single quotes to escape a bit of a challenge).

Depending on what you are trying to do in APEX, however, you may want something a little different. For example, if you are trying to create a report based on this, a regular (non-interactive) report can be populated either from a SQL statement or a function that returns a SQL statement. If that's what you're trying to do, you'd want something like

DECLARE
  l_sql_stmt varchar2(1000);
  l_tmp_space varchar2(1000);
  l_database  varchar2(100) := <<db link name>>;
BEGIN
  l_sql_stmt := 'select ''Total temp space available in ' ||l_database  || ' is '' || sum(bytes)/1024/1024 ||'' mb'' from v$tempfile@' || l_database;
  dbms_output.put_line( l_sql_stmt );
  RETURN l_sql_stmt;
END;

来源：https://stackoverflow.com/questions/10853586/variable-for-database-link-name