Thread: How can I find a schema that a table belong to?
Hi, I am trying to tidy up my perl script that runs as a cgi and allows remote users (aka me) to interact with my Pg database. I primarily want to use this tool as a way for my iPad to browse my data base. It seems to be working quite well but one certainly does not want to 'select * from ginormous_table'. I am trying to build a 'describe' function. ie if the user types "describe tablename" in the sql box I want to display some interesting attributes for that table, mainly names and data types for each of the columns. I have done this in other programs but I forced the user to specify a schema qualified name ( and mimiced what psql -E did). So I guess the question is: Given a bare table name, how can I recover the schema qualified name with whatever the current search path happens to be? This task has to be done using simple sql from the perl dbi. Thanks, Jerry
Jerry LeVan, 19.01.2011 17:35: > > So I guess the question is: > Given a bare table name, how can I recover the schema > qualified name with whatever the current search path happens > to be? > SELECT table_schema FROM information_schema.tables WHERE table_name = 'your_table' ;
Thomas Kellerer <spam_eater@gmx.net> writes: > Jerry LeVan, 19.01.2011 17:35: >> So I guess the question is: >> Given a bare table name, how can I recover the schema >> qualified name with whatever the current search path happens >> to be? > SELECT table_schema > FROM information_schema.tables > WHERE table_name = 'your_table' > ; That's not going to work, at least not in the interesting case where you have more than one candidate table --- that SELECT will list all of 'em. In most cases the answer to this type of problem is "use regclass", but regclass doesn't quite solve Jerry's problem because it won't schema-qualify the name if the table is visible in the search path. The best solution I can think of is select nspname from pg_namespace n join pg_class c on n.oid = c.relnamespace where c.oid = 'my_table_name'::regclass; which works but seems a bit brute-force. regards, tom lane
Tom Lane, 19.01.2011 19:19: >> SELECT table_schema >> FROM information_schema.tables >> WHERE table_name = 'your_table' >> ; > > That's not going to work, at least not in the interesting case where you > have more than one candidate table --- that SELECT will list all of 'em. > Ah, right. I was a buit too quick with my answer. Regards Thomas
Tom Lane, 19.01.2011 19:19: >>> Given a bare table name, how can I recover the schema >>> qualified name with whatever the current search path happens >>> to be? > >> SELECT table_schema >> FROM information_schema.tables >> WHERE table_name = 'your_table' >> ; > > That's not going to work, at least not in the interesting case where you > have more than one candidate table --- that SELECT will list all of 'em. What about something like this: SELECT tbl.table_schema, tbl.table_name, pe.path_position FROM information_schema.tables tbl JOIN ( SELECT path_element, row_number() over () as path_position FROM ( SELECT trim(unnest(string_to_array(setting, ','))) as path_element FROM pg_settings WHERE name = 'search_path' ) t ) pe on tbl.table_schema = pe.path_element WHERE tbl.table_name = 'your_table' ORDER BY pe.path_position; This will list each table together with the index of the schema in the search path in the order of the schemas listed inthe search path. The only thing I'm unsure about is whether unnest() will always preserve the order of the array. Regards Thomas