select relname as tabname,cast(obj_description(relfilenode,'pg_class') as varchar) as comment from pg_class c 
where relkind = 'r' and relname not like 'pg_%' and relname not like 'sql_%' order by relname

SELECT col_description(a.attrelid,a.attnum) as comment,format_type(a.atttypid,a.atttypmod) as type,a.attname as name, a.attnotnull as notnull 
FROM pg_class as c,pg_attribute as a where c.relname = '表名' and a.attrelid = c.oid and a.attnum>0

SELECT
 string_agg(DISTINCT t3.attname,',') AS primaryKeyColumn
 ,t4.tablename AS tableName
 , string_agg(cast(obj_description(relfilenode,'pg_class') as varchar),'') as comment
FROM
 pg_constraint t1
 INNER JOIN pg_class t2 ON t1.conrelid = t2.oid
 INNER JOIN pg_attribute t3 ON t3.attrelid = t2.oid AND array_position(t1.conkey,t3.attnum) is not null
 INNER JOIN pg_tables t4 on t4.tablename = t2.relname
 INNER JOIN pg_index t5 ON t5.indrelid = t2.oid AND t3.attnum = ANY (t5.indkey)
 LEFT JOIN pg_description t6 on t6.objoid=t3.attrelid and t6.objsubid=t3.attnum
WHERE t1.contype = 'p'
  AND length(t3.attname) > 0
  AND t2.oid = '表名' :: regclass
 group by t4.tablename