postgresql數據庫 查詢表名、備注及字段、長度、是否可控、是否主鍵等信息

項目中需要采集postgresql的元數據信息，需查詢pgsql 的表名以及表中字段的各信息，

通過查找資料，記之如下：

查詢表名及備注SQL

select pc.relname as table_name, pd.description as comment from pg_catalog.pg_class pc join pg_catalog.pg_description pd on pc.oid = pd.objoid where pc.relname = 'tableName'
    and pd.objsubid = 0

獲取指定表的字段名稱、長度、是否為空、是否主鍵等信息

SELECT pc.relname AS tableName, pa.attname AS columnName, pt.typname AS columnType, ( CASE WHEN pa.attlen > 0 THEN pa.attlen ELSE pa.atttypmod - 4 END ) AS columnLength, pa.attnotnull AS isNullAble, ( CASE WHEN ( SELECT COUNT(*) FROM pg_constraint WHERE conrelid = pa.attrelid AND conkey[1]= attnum AND contype = 'p' ) > 0 THEN TRUE ELSE FALSE END ) AS isPrimary, pd.description AS columnDescription FROM pg_class pc, pg_attribute pa, pg_type pt, pg_description pd WHERE pc.oid = pa.attrelid AND pt.oid = pa.atttypid AND pd.objoid = pa.attrelid AND pd.objsubid = pa.attnum AND pc.relname = 'table_name' 
    ORDER BY pc.relname DESC, pa.attnum ASC