pgAdmin III macros: get table fields

When writing SQL statements of Stored Procedure code in pgAdmin, it is quite often quite handy to know the names and restrictions on the fields of some table.

Here is a simple macro that can be assigned to a key combination in pgAdmin -> Query Window -> Macros -> Manage macros...

select quote_ident(nspname) || '.' || quote_ident(relname) as table_name, 
       quote_ident(attname) as field_name, 
       format_type(atttypid,atttypmod) as field_type, 
       case when attnotnull then ' NOT NULL' else '' end as null_constraint,
       case when atthasdef then 'DEFAULT ' || 
                                ( select pg_get_expr(adbin, attrelid) 
                                    from pg_attrdef 
                                   where adrelid = attrelid and adnum = attnum )::text else '' 
       end as dafault_value,
       case when nullif(confrelid, 0) is not null 
            then confrelid::regclass::text || '( ' || 
                 array_to_string( ARRAY( select quote_ident( fa.attname ) 
                                           from pg_attribute as fa 
                                          where fa.attnum = ANY ( confkey ) 
                                            and fa.attrelid = confrelid
                                          order by fa.attnum 
                                        ), ',' 
                                 ) || ' )' 
            else '' end as references_to
  from pg_attribute 
       left outer join pg_constraint on conrelid = attrelid 
                                    and attnum = conkey[1] 
                                    and array_upper( conkey, 1 ) = 1,
 where pg_class.oid = attrelid
   and pg_namespace.oid = relnamespace
   and pg_class.oid = btrim( '$SELECTION$' )::regclass::oid
   and attnum > 0
   and not attisdropped
 order by attrelid, attnum;

Just select a table name, that you are interested in, and press the key binding, that you selected for that macros. pgAdmin will execute the query and show the list of all the columns of that table, including default values and foreign key references...

My preferred key binding is CTRL+1

Type of NULL is important

The following SQL query shows how different can be the result of concatenating arrays with NULL values:

select '{e1,e2}'::text[] || 't'::text     as normal_array_concatenation,
       NULL::text[] || 't'::text         as appending_element_to_existing_NULL_value_array, 
       NULL || 't'::text                 as appending_element_to_NULL_value,
       '{e1,e2}'::text[] || NULL::text   as appending_typed_NULL,
       '{e1,e2}'::text[] || NULL::text[] as appending_typed_NULL_array;

The result of the execution (on 9.0) is:

─[ RECORD 1 ]──────────────────────────────────┬─────────────
normal_array_concatenation                     │ {e1,e2,t}
appending_element_to_existing_null_value_array │ {t}
appending_element_to_null_value                │ 
appending_typed_null                           │ {e1,e2,NULL}
appending_typed_null_array                     │ {e1,e2}

That explains why one can simply initialize a new array variable in PL/pgSQL and then immediately start concatenating it with values, not pre-initializing it with an empty array (that you have to do when you want to populate a text string... you cannot just take a NULL::text variable and start concatenating strings to it, you have to first pre-inizialize it with en empty string, but with arrays you can).

Another very important issue, that is related to that beheviour of arrays, is that when creating dynamic SQL queries for EXECUTE command in PL/pgSQL you SHOULD always put explicit type casts to the variables that you quote using quote_literal() or quote_nullable() when building dynamic queries:

  r text[];
  t text   := NULL;
  a text[] := NULL;

  SELECT '{e1,e2}'::text[] || a INTO r;
  RAISE INFO 'array concatenate: r is %', r;

  EXECUTE $$SELECT '{e1,e2}'::text[] || $$ || quote_nullable(a) || $$::text[] $$ INTO r;
  RAISE INFO 'array concatenate from EXECUTE: r is %', r;

  SELECT '{e1,e2}'::text[] || t INTO r;
  RAISE INFO 'array append: r is %', r;

  EXECUTE $$SELECT '{e1,e2}'::text[] || $$ || quote_nullable(t) || $$::text $$ INTO r;
  RAISE INFO 'array append from EXECUTE: r is %', r;

  /* These 2 examples will fail on the runtime 
     throwing exception (operator is not unique: text[] || unknown)
  --EXECUTE $$SELECT '{e1,e2}'::text[] || $$ || quote_nullable(a) INTO r;
  --RAISE INFO 'r is %', r;
  --EXECUTE $$SELECT '{e1,e2}'::text[] || $$ || quote_nullable(t) INTO r;
  --RAISE INFO 'r is %', r;