12 Matching Annotations
  1. Jan 2020
    1. Which to use? ANY is a later, more versatile addition, it can be combined with any binary operator returning a boolean value. IN burns down to a special case of ANY. In fact, its second form is rewritten internally: IN is rewritten with = ANY NOT IN is rewritten with <> ALL
  2. Dec 2019
    1. Practical highlights in my opinion:

      • It's important to know about data padding in PG.
      • Be conscious when modelling data tables about columns ordering, but don't be pure-school and do it in a best-effort basis.
      • Gains up to 25% in wasted storage are impressive but always keep in mind the scope of the system. For me, gains are not worth it in the short-term. Whenever a system grows, it is possible to migrate data to more storage-efficient tables but mind the operative burder.

      Here follows my own commands on trying the article points. I added - pg_column_size(row()) on each projection to have clear absolute sizes.

      -- How does row function work?
      
      SELECT pg_column_size(row()) AS empty,
             pg_column_size(row(0::SMALLINT)) AS byte2,
             pg_column_size(row(0::BIGINT)) AS byte8,
             pg_column_size(row(0::SMALLINT, 0::BIGINT)) AS byte16,
             pg_column_size(row(''::TEXT)) AS text0,
             pg_column_size(row('hola'::TEXT)) AS text4,
             0 AS term
      ;
      
      -- My own take on that
      
      SELECT pg_column_size(row()) AS empty,
             pg_column_size(row(uuid_generate_v4())) AS uuid_type,
             pg_column_size(row('hola mundo'::TEXT)) AS text_type,
             pg_column_size(row(uuid_generate_v4(), 'hola mundo'::TEXT)) AS uuid_text_type,
             pg_column_size(row('hola mundo'::TEXT, uuid_generate_v4())) AS text_uuid_type,
             0 AS term
      ;
      
      CREATE TABLE user_order (
        is_shipped    BOOLEAN NOT NULL DEFAULT false,
        user_id       BIGINT NOT NULL,
        order_total   NUMERIC NOT NULL,
        order_dt      TIMESTAMPTZ NOT NULL,
        order_type    SMALLINT NOT NULL,
        ship_dt       TIMESTAMPTZ,
        item_ct       INT NOT NULL,
        ship_cost     NUMERIC,
        receive_dt    TIMESTAMPTZ,
        tracking_cd   TEXT,
        id            BIGSERIAL PRIMARY KEY NOT NULL
      );
      
      SELECT a.attname, t.typname, t.typalign, t.typlen
        FROM pg_class c
        JOIN pg_attribute a ON (a.attrelid = c.oid)
        JOIN pg_type t ON (t.oid = a.atttypid)
       WHERE c.relname = 'user_order'
         AND a.attnum >= 0
       ORDER BY a.attnum;
      
      -- What is it about pg_class, pg_attribute and pg_type tables? For future investigation.
      
      -- SELECT sum(t.typlen)
      -- SELECT t.typlen
      SELECT a.attname, t.typname, t.typalign, t.typlen
        FROM pg_class c
        JOIN pg_attribute a ON (a.attrelid = c.oid)
        JOIN pg_type t ON (t.oid = a.atttypid)
       WHERE c.relname = 'user_order'
         AND a.attnum >= 0
       ORDER BY a.attnum
      ;
      
      -- Whoa! I need to master mocking data directly into db.
      
      INSERT INTO user_order (
          is_shipped, user_id, order_total, order_dt, order_type,
          ship_dt, item_ct, ship_cost, receive_dt, tracking_cd
      )
      SELECT true, 1000, 500.00, now() - INTERVAL '7 days',
             3, now() - INTERVAL '5 days', 10, 4.99,
             now() - INTERVAL '3 days', 'X5901324123479RROIENSTBKCV4'
        FROM generate_series(1, 1000000);
      
      -- New item to learn, pg_relation_size. 
      
      SELECT pg_relation_size('user_order') AS size_bytes,
             pg_size_pretty(pg_relation_size('user_order')) AS size_pretty;
      
      SELECT * FROM user_order LIMIT 1;
      
      SELECT pg_column_size(row(0::NUMERIC)) - pg_column_size(row()) AS zero_num,
             pg_column_size(row(1::NUMERIC)) - pg_column_size(row()) AS one_num,
             pg_column_size(row(9.9::NUMERIC)) - pg_column_size(row()) AS nine_point_nine_num,
             pg_column_size(row(1::INT2)) - pg_column_size(row()) AS int2,
             pg_column_size(row(1::INT4)) - pg_column_size(row()) AS int4,
             pg_column_size(row(1::INT2, 1::NUMERIC)) - pg_column_size(row()) AS int2_one_num,
             pg_column_size(row(1::INT4, 1::NUMERIC)) - pg_column_size(row()) AS int4_one_num,
             pg_column_size(row(1::NUMERIC, 1::INT4)) - pg_column_size(row()) AS one_num_int4,
             0 AS term
      ;
      
      SELECT pg_column_size(row(''::TEXT)) - pg_column_size(row()) AS empty_text,
             pg_column_size(row('a'::TEXT)) - pg_column_size(row()) AS len1_text,
             pg_column_size(row('abcd'::TEXT)) - pg_column_size(row()) AS len4_text,
             pg_column_size(row('abcde'::TEXT)) - pg_column_size(row()) AS len5_text,
             pg_column_size(row('abcdefgh'::TEXT)) - pg_column_size(row()) AS len8_text,
             pg_column_size(row('abcdefghi'::TEXT)) - pg_column_size(row()) AS len9_text,
             0 AS term
      ;
      
      SELECT pg_column_size(row(''::TEXT, 1::INT4)) - pg_column_size(row()) AS empty_text_int4,
             pg_column_size(row('a'::TEXT, 1::INT4)) - pg_column_size(row()) AS len1_text_int4,
             pg_column_size(row('abcd'::TEXT, 1::INT4)) - pg_column_size(row()) AS len4_text_int4,
             pg_column_size(row('abcde'::TEXT, 1::INT4)) - pg_column_size(row()) AS len5_text_int4,
             pg_column_size(row('abcdefgh'::TEXT, 1::INT4)) - pg_column_size(row()) AS len8_text_int4,
             pg_column_size(row('abcdefghi'::TEXT, 1::INT4)) - pg_column_size(row()) AS len9_text_int4,
             0 AS term
      ;
      
      SELECT pg_column_size(row(1::INT4, ''::TEXT)) - pg_column_size(row()) AS int4_empty_text,
             pg_column_size(row(1::INT4, 'a'::TEXT)) - pg_column_size(row()) AS int4_len1_text,
             pg_column_size(row(1::INT4, 'abcd'::TEXT)) - pg_column_size(row()) AS int4_len4_text,
             pg_column_size(row(1::INT4, 'abcde'::TEXT)) - pg_column_size(row()) AS int4_len5_text,
             pg_column_size(row(1::INT4, 'abcdefgh'::TEXT)) - pg_column_size(row()) AS int4_len8_text,
             pg_column_size(row(1::INT4, 'abcdefghi'::TEXT)) - pg_column_size(row()) AS int4_len9_text,
             0 AS term
      ;
      
      SELECT pg_column_size(row()) - pg_column_size(row()) AS empty_row,
             pg_column_size(row(''::TEXT)) - pg_column_size(row()) AS no_text,
             pg_column_size(row('a'::TEXT)) - pg_column_size(row()) AS min_text,
             pg_column_size(row(1::INT4, 'a'::TEXT)) - pg_column_size(row()) AS two_col,
             pg_column_size(row('a'::TEXT, 1::INT4)) - pg_column_size(row()) AS round4;
      
      SELECT pg_column_size(row()) - pg_column_size(row()) AS empty_row,
             pg_column_size(row(1::SMALLINT)) - pg_column_size(row()) AS int2,
             pg_column_size(row(1::INT)) - pg_column_size(row()) AS int4,
             pg_column_size(row(1::BIGINT)) - pg_column_size(row()) AS int8,
             pg_column_size(row(1::SMALLINT, 1::BIGINT)) - pg_column_size(row()) AS padded,
             pg_column_size(row(1::INT, 1::INT, 1::BIGINT)) - pg_column_size(row()) AS not_padded;
      
      SELECT a.attname, t.typname, t.typalign, t.typlen
        FROM pg_class c
        JOIN pg_attribute a ON (a.attrelid = c.oid)
        JOIN pg_type t ON (t.oid = a.atttypid)
       WHERE c.relname = 'user_order'
         AND a.attnum >= 0
       ORDER BY t.typlen DESC;
      
      DROP TABLE user_order;
      
      CREATE TABLE user_order (
        id            BIGSERIAL PRIMARY KEY NOT NULL,
        user_id       BIGINT NOT NULL,
        order_dt      TIMESTAMPTZ NOT NULL,
        ship_dt       TIMESTAMPTZ,
        receive_dt    TIMESTAMPTZ,
        item_ct       INT NOT NULL,
        order_type    SMALLINT NOT NULL,
        is_shipped    BOOLEAN NOT NULL DEFAULT false,
        order_total   NUMERIC NOT NULL,
        ship_cost     NUMERIC,
        tracking_cd   TEXT
      );
      
      -- And, what about other varying size types as JSONB?
      
      SELECT pg_column_size(row('{}'::JSONB)) - pg_column_size(row()) AS empty_jsonb,
             pg_column_size(row('{}'::JSONB, 0::INT4)) - pg_column_size(row()) AS empty_jsonb_int4,
             pg_column_size(row(0::INT4, '{}'::JSONB)) - pg_column_size(row()) AS int4_empty_jsonb,
             pg_column_size(row('{"a": 1}'::JSONB)) - pg_column_size(row()) AS basic_jsonb,
             pg_column_size(row('{"a": 1}'::JSONB, 0::INT4)) - pg_column_size(row()) AS basic_jsonb_int4,
             pg_column_size(row(0::INT4, '{"a": 1}'::JSONB)) - pg_column_size(row()) AS int4_basic_jsonb,
             0 AS term;
      
  3. Nov 2019
  4. Nov 2018
    1. Unfortunately you need to install the postgresql package, because Homebrew does not currently provide a standalone libpq package.

      Interestingly enough, I found that that "brew install libpq" installed from "https://ftp.postgresql.org/pub/source/v11.0/postgresql-11.0.tar.bz2 ... Summary 🍺 /usr/local/Cellar/libpq/11.0: 2,561 files, 27.2MB, built in 4 minutes 30 seconds."

      Mac Pro on Mac OX 10.11.6.

  5. Sep 2017
    1. PostgreSQL連接Python

      python连接postgresql,非常简单,基本跟mylsql一样,通过cursor来执行

  6. May 2016
    1. Because this is not always needed, and there are many choices available on how to index, declaration of a foreign key constraint does not automatically create an index on the referencing columns.

      PostgreSQL does not automatically create an index for foreign key constraints, it does however for primary keys.