PostgreSQL 的 Table 相關筆記

欄位型別

數值型別

金額型別

numeric, int, 和 bigint 型別可以轉為 money. 從 real 和 double precision 則需要先轉為 numeric first, 例如

SELECT '12.34'::float8::numeric::money;

money 可以無損轉換為 numeric, 轉換為其他型別則會有精度損失, 例如

SELECT '52093.89'::money::numeric::float8;

字串型別

二進制型別

二進制表示, 使用 \x sequence

SELECT '\xDEADBEEF';

時間型別

其中, interval型別可以為以下值

YEAR
MONTH
DAY
HOUR
MINUTE
SECOND
YEAR TO MONTH
DAY TO HOUR
DAY TO MINUTE
DAY TO SECOND
HOUR TO MINUTE
HOUR TO SECOND
MINUTE TO SECOND

布爾型別

列舉型別

宣告

CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');

使用

CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');
CREATE TABLE person (
    name text,
    current_mood mood
);
INSERT INTO person VALUES ('Moe', 'happy');
SELECT * FROM person WHERE current_mood = 'happy';
 name | current_mood 
------+--------------
 Moe  | happy
(1 row)

排序和比較

INSERT INTO person VALUES ('Larry', 'sad');
INSERT INTO person VALUES ('Curly', 'ok');
SELECT * FROM person WHERE current_mood > 'sad';
 name  | current_mood 
-------+--------------
 Moe   | happy
 Curly | ok
(2 rows)

SELECT * FROM person WHERE current_mood > 'sad' ORDER BY current_mood;
 name  | current_mood 
-------+--------------
 Curly | ok
 Moe   | happy
(2 rows)

SELECT name
FROM person
WHERE current_mood = (SELECT MIN(current_mood) FROM person);
 name  
-------
 Larry
(1 row)

地理位置型別

網路地址型別

inet 和 cidr 的區別
二者最關鍵的區別在于, inet 允許IP地址在掩碼區域外有非零值, 例如 "192.168.0.1/24", 這個值對于 cidr 是不允許的.

如果不喜歡 inet 或 cidr 輸出的格式, 可以使用 host, text 和 abbrev 這些函式進行處理.

二進制串型別

使用0和1表示的字串, sql示例

CREATE TABLE test (a BIT(3), b BIT VARYING(5));
INSERT INTO test VALUES (B'101', B'00');
INSERT INTO test VALUES (B'10', B'101');

ERROR:  bit string length 2 does not match type bit(3)

INSERT INTO test VALUES (B'10'::bit(3), B'101');
SELECT * FROM test;

  a  |  b
-----+-----
 101 | 00
 100 | 101

文本搜索型別

PostgreSQL provides two data types that are designed to support full text search, which is the activity of searching through a collection of natural-language documents to locate those that best match a query. The tsvector type represents a document in a form optimized for text search; the tsquery type similarly represents a text query. Chapter 12 provides a detailed explanation of this facility, and Section 9.13 summarizes the related functions and operators.

tsvector, tsquery

UUID型別

欄位長16 byte(128-bit), 用于分布式系統可以提供更好的唯一性保證(相對于自增序列). 一個 UUID 是一組短橫線分隔的十六進制小寫數字,
格式為: 一組8位, 三組4位, 最后是一組12位, 一共32位組成128bit. 例如

a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11

XML型別

XMLPARSE ( { DOCUMENT | CONTENT } value)
XMLPARSE (DOCUMENT '<?xml version="1.0"?><book><title>Manual</title><chapter>...</chapter></book>')
XMLPARSE (CONTENT 'abc<foo>bar</foo><bar>foo</bar>')

XMLSERIALIZE ( { DOCUMENT | CONTENT } value AS type )

JSON型別

陣列型別

CREATE TABLE sal_emp (
    name            text,
    pay_by_quarter  integer[],
    schedule        text[][]
);

CREATE TABLE tictactoe (
    squares   integer[3][3]
);

增和查

INSERT INTO sal_emp
    VALUES ('Bill',
    '{10000, 10000, 10000, 10000}',
    '{{"meeting", "lunch"}, {"training", "presentation"}}');

INSERT INTO sal_emp
    VALUES ('Carol',
    '{20000, 25000, 25000, 25000}',
    '{{"breakfast", "consulting"}, {"meeting", "lunch"}}');
The result of the previous two inserts looks like this:

SELECT * FROM sal_emp;
 name  |      pay_by_quarter       |                 schedule
-------+---------------------------+-------------------------------------------
 Bill  | {10000,10000,10000,10000} | {{meeting,lunch},{training,presentation}}
 Carol | {20000,25000,25000,25000} | {{breakfast,consulting},{meeting,lunch}}
(2 rows)

-- 使用 ARRAY
INSERT INTO sal_emp
    VALUES ('Bill',
    ARRAY[10000, 10000, 10000, 10000],
    ARRAY[['meeting', 'lunch'], ['training', 'presentation']]);

INSERT INTO sal_emp
    VALUES ('Carol',
    ARRAY[20000, 25000, 25000, 25000],
    ARRAY[['breakfast', 'consulting'], ['meeting', 'lunch']]);


SELECT name FROM sal_emp WHERE pay_by_quarter[1] <> pay_by_quarter[2];

 name
-------
 Carol
(1 row)


SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';

        schedule
------------------------
 {{meeting},{training}}
(1 row)


SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';

                 schedule
-------------------------------------------
 {{meeting,lunch},{training,presentation}}
(1 row)

改

UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}'
    WHERE name = 'Carol';

-- 使用 ARRAY
UPDATE sal_emp SET pay_by_quarter = ARRAY[25000,25000,27000,27000]
    WHERE name = 'Carol';

自定義型別, 組合型別

CREATE TYPE complex AS (
    r       double precision,
    i       double precision
);

CREATE TYPE inventory_item AS (
    name            text,
    supplier_id     integer,
    price           numeric
);

CREATE TABLE on_hand (
    item      inventory_item,
    count     integer
);

INSERT INTO on_hand VALUES (ROW('fuzzy dice', 42, 1.99), 1000);

CREATE FUNCTION price_extension(inventory_item, integer) RETURNS numeric
AS 'SELECT $1.price * $2' LANGUAGE SQL;

SELECT price_extension(item, 10) FROM on_hand;

CREATE TABLE inventory_item (
    name            text,
    supplier_id     integer REFERENCES suppliers,
    price           numeric CHECK (price > 0)
);

Table相關SQL

建表 CREATE TABLE

建表說明: https://www.postgresql.org/docs/14/sql-createtable.html

完整的建表語法

CREATE [ { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name ( [
  { column_name data_type [ COMPRESSION compression_method ] [ COLLATE collation ] [ column_constraint [ ... ] ]
    | table_constraint
    | LIKE source_table [ like_option ... ] }
    [, ... ]
] )
[ INHERITS ( parent_table [, ... ] ) ]
[ PARTITION BY { RANGE | LIST | HASH } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ USING method ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]

-- column_constraint 欄位約束的格式
[ CONSTRAINT constraint_name ]
{ NOT NULL |
  NULL |
  CHECK ( expression ) [ NO INHERIT ] |
  DEFAULT default_expr |
  GENERATED ALWAYS AS ( generation_expr ) STORED |
  GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] |
  UNIQUE index_parameters |
  PRIMARY KEY index_parameters |
  REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
    [ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

-- table_constraint 表約束的格式
[ CONSTRAINT constraint_name ]
{ CHECK ( expression ) [ NO INHERIT ] |
  UNIQUE ( column_name [, ... ] ) index_parameters |
  PRIMARY KEY ( column_name [, ... ] ) index_parameters |
  EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters [ WHERE ( predicate ) ] |
  FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

還有OF type_name和PARTITION OF parent_table兩種, 比較少用.

TEMPORARY | TEMP

臨時表, 在session結束后自動drop

UNLOGGED

對UNLOGGED表的寫入不記入 write-ahead 日志, 所以比普通表快. 如果資料庫崩潰(crash)或非常關機, UNLOGGED表會被自動truncate. UNLOGGED表不能replicated, 基于UNLOGGED表的索引也會是UNLOGGED的.

COMPRESSION

壓縮僅用于變長欄位型別, and is used only when the column's storage mode is main or extended

PARTITION BY { RANGE | LIST | HASH } ( { column_name | ( expression ) } [ opclass ] [, ...] )

用于對表進行磁區. The table thus created is called a partitioned table. The parenthesized list of columns or expressions forms the partition key for the table. When using range or hash partitioning, the partition key can include multiple columns or expressions (up to 32, but this limit can be altered when building PostgreSQL), but for list partitioning, the partition key must consist of a single column or expression.

Range and list partitioning require a btree operator class, while hash partitioning requires a hash operator class. If no operator class is specified explicitly, the default operator class of the appropriate type will be used; if no default operator class exists, an error will be raised. When hash partitioning is used, the operator class used must implement support function 2 (see Section 38.16.3 for details).

表磁區后, 會變成一系列子表, 原表本身變成空表. 向原表的寫入, 會路由到對應的子表, 如果對應的磁區不存在就會報錯. 磁區表不支持 EXCLUDE 約束, 但是在子表中可以定義.

NOT NULL, NULL, DEFAULT, UNIQUE, PRIMARY KEY

和MySQL用法一樣

GENERATED ALWAYS AS ( generation_expr ) STORED

類似于view, 這種欄位由其他欄位(非generated)生成, 不能寫只能讀

GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ]

表示此欄位為ID欄位, 使用一個系結的sequence自動賦值, 并且這個欄位一定是NOT NULL. This clause creates the column as an identity column. It will have an implicit sequence attached to it and the column in new rows will automatically have values from the sequence assigned to it. Such a column is implicitly NOT NULL.

The clauses ALWAYS and BY DEFAULT determine how explicitly user-specified values are handled in INSERT and UPDATE commands.

TABLESPACE tablespace_name

表空間, 未指定則使用 default_tablespace, 如果是臨時表, 則使用 temp_tablespaces.

建表示例

設定主鍵

CREATE TABLE films (
    code        char(5) CONSTRAINT firstkey PRIMARY KEY,
    title       varchar(40) NOT NULL,
    did         integer NOT NULL,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute
);

CREATE TABLE distributors (
     did    integer PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
     name   varchar(40) NOT NULL CHECK (name <> '')
);

CREATE TABLE films (
    code        char(5),
    title       varchar(40),
    did         integer,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute,
    CONSTRAINT code_title PRIMARY KEY(code,title)
);

-- 下面兩個是等價的
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    PRIMARY KEY(did)
);

CREATE TABLE distributors (
    did     integer PRIMARY KEY,
    name    varchar(40)
);

二維陣列欄位

CREATE TABLE array_int (
    vector  int[][]
);

唯一約束欄位

CREATE TABLE films (
    code        char(5),
    title       varchar(40),
    did         integer,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute,
    CONSTRAINT production UNIQUE(date_prod)
);

CREATE TABLE distributors (
    did     integer,
    name    varchar(40) UNIQUE
);

運算式約束欄位

CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    CONSTRAINT con1 CHECK (did > 100 AND name <> '')
);

設定欄位默認值

CREATE TABLE distributors (
    name      varchar(40) DEFAULT 'Luso Films',
    did       integer DEFAULT nextval('distributors_serial'),
    modtime   timestamp DEFAULT current_timestamp
);

非空約束

CREATE TABLE distributors (
    did     integer CONSTRAINT no_null NOT NULL,
    name    varchar(40) NOT NULL
);

對表進行磁區

CREATE TABLE measurement (
    logdate         date not null,
    peaktemp        int,
    unitsales       int
) PARTITION BY RANGE (logdate);

-- 磁區依據多個欄位
CREATE TABLE measurement_year_month (
    logdate         date not null,
    peaktemp        int,
    unitsales       int
) PARTITION BY RANGE (EXTRACT(YEAR FROM logdate), EXTRACT(MONTH FROM logdate));

-- 使用list磁區
CREATE TABLE cities (
    city_id      bigserial not null,
    name         text not null,
    population   bigint
) PARTITION BY LIST (left(lower(name), 1));

-- 使用hash磁區
CREATE TABLE orders (
    order_id     bigint not null,
    cust_id      bigint not null,
    status       text
) PARTITION BY HASH (order_id);

-- 使用區間磁區
CREATE TABLE measurement_y2016m07
    PARTITION OF measurement (
    unitsales DEFAULT 0
) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');

分別創建 表measurement_year_month 的各個磁區子表

CREATE TABLE measurement_ym_older
    PARTITION OF measurement_year_month
    FOR VALUES FROM (MINVALUE, MINVALUE) TO (2016, 11);

CREATE TABLE measurement_ym_y2016m11
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2016, 11) TO (2016, 12);

CREATE TABLE measurement_ym_y2016m12
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2016, 12) TO (2017, 01);

CREATE TABLE measurement_ym_y2017m01
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2017, 01) TO (2017, 02);

或者

CREATE TABLE orders_p1 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 0);
CREATE TABLE orders_p2 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 1);
CREATE TABLE orders_p3 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 2);
CREATE TABLE orders_p4 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 3);

對于以上的磁區方式, 可以設定一個默認子磁區

CREATE TABLE cities_partdef
    PARTITION OF cities DEFAULT;

修改表 ALTER TABLE

添加欄位

ALTER TABLE distributors ADD COLUMN address varchar(30);

洗掉欄位

ALTER TABLE distributors DROP COLUMN address RESTRICT;

修改欄位型別

ALTER TABLE distributors
    ALTER COLUMN address TYPE varchar(80),
    ALTER COLUMN name TYPE varchar(100);

ALTER TABLE foo
    ALTER COLUMN foo_timestamp SET DATA TYPE timestamp with time zone
    USING
        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second';

ALTER TABLE foo
    ALTER COLUMN foo_timestamp DROP DEFAULT,
    ALTER COLUMN foo_timestamp TYPE timestamp with time zone
    USING
        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',
    ALTER COLUMN foo_timestamp SET DEFAULT now();

欄位更名

ALTER TABLE distributors RENAME COLUMN address TO city;

表更名

ALTER TABLE distributors RENAME TO suppliers;

欄位添加非空限制, 洗掉非空限制

ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;
ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;

對表和子表添加和洗掉check限制

ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);
ALTER TABLE distributors DROP CONSTRAINT zipchk;

僅洗掉一個表的check限制

ALTER TABLE ONLY distributors DROP CONSTRAINT zipchk;

自增序列 SEQUENCE

查看資料庫中的sequence

select * from pg_sequences order by sequencename asc

列出sequence與table的關聯

select sn.nspname as seq_schema,
       s.relname as seqname,
       st.nspname as tableschema,
       t.relname as tablename,
       at.attname as columname
  from pg_class s
  join pg_namespace sn on sn.oid = s.relnamespace
  join pg_depend d on d.refobjid = s.oid 
  join pg_attrdef a on d.objid = a.oid
  join pg_attribute at on at.attrelid = a.adrelid and at.attnum = a.adnum
  join pg_class t on t.oid = a.adrelid
  join pg_namespace st on st.oid = t.relnamespace
 where s.relkind = 'S'
   and d.classid = 'pg_attrdef'::regclass
   and d.refclassid = 'pg_class'::regclass
 order by s.relname asc

如果欄位型別為serial, 會隱含創建sequence, 例如下面的陳述句會產生三個sequence

create table foo(id serial, v integer);
create table boo(id_boo serial, v integer);
create sequence omega;
create table bubu(id integer default nextval('omega'), v integer);

┌────────────┬────────────────┬─────────────┬───────────┬───────────┐
│ seq_schema │    seqname     │ tableschema │ tablename │ columname │
╞════════════╪════════════════╪═════════════╪═══════════╪═══════════╡
│ public     │ foo_id_seq     │ public      │ foo       │ id        │
│ public     │ boo_id_boo_seq │ public      │ boo       │ id_boo    │
│ public     │ omega          │ public      │ bubu      │ id        │
└────────────┴────────────────┴─────────────┴───────────┴───────────┘

如果執行

create table foo(
    id serial primary key, 
    val integer
);

實際看到的表結構為

CREATE TABLE "public"."foo" (
  "id" int4 NOT NULL DEFAULT nextval('foo_id_seq'::regclass),
  "val" int4,
  CONSTRAINT "foo_pkey" PRIMARY KEY ("id")
)
;

ALTER TABLE "public"."foo" 
  OWNER TO "dbuser";

參考

• https://www.postgresql.org/docs/14/datatype.html
• https://www.postgresql.org/docs/14/sql-createtable.html
• https://www.postgresql.org/docs/14/sql-altertable.html

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