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<?xml version="1.0" encoding="UTF-8" standalone="no"?>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>7.5. Function</title><link rel="stylesheet" type="text/css" href="/docbook.css" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="home" href="index.html" title="Netkiller PostgreSQL 手札" /><link rel="up" href="sql.html" title="第 7 章 SQL" /><link rel="prev" href="returning.html" title="7.4. returning" /><link rel="next" href="ch08.html" title="第 8 章事务处理与锁" /></head><body><a xmlns="" href="//www.netkiller.cn/">Home</a> |

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<a xmlns="" href="//www.netkiller.cn/home/about.html">About</a><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">7.5. Function</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="returning.html">上一页</a> </td><th width="60%" align="center">第 7 章 SQL</th><td width="20%" align="right"> <a accesskey="n" href="ch08.html">下一页</a></td></tr></table><hr /></div><table xmlns=""><tr><td><iframe src="//ghbtns.com/github-btn.html?user=netkiller&repo=netkiller.github.io&type=watch&count=true&size=large" height="30" width="170" frameborder="0" scrolling="0" style="width:170px; height: 30px;" allowTransparency="true"></iframe></td><td><iframe src="//ghbtns.com/github-btn.html?user=netkiller&repo=netkiller.github.io&type=fork&count=true&size=large" height="30" width="170" frameborder="0" scrolling="0" style="width:170px; height: 30px;" allowTransparency="true"></iframe></td><td><iframe src="//ghbtns.com/github-btn.html?user=netkiller&type=follow&count=true&size=large" height="30" width="240" frameborder="0" scrolling="0" style="width:240px; height: 30px;" allowTransparency="true"></iframe></td></tr></table><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="sql.function"></a>7.5. Function</h2></div></div></div>

<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="generate_series"></a>7.5.1. generate_series</h3></div></div></div>

<p>生成序列数</p>

test=# select generate_series(1,10) as id;

----

(10 rows)

</pre>

</div>

<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idp49"></a>7.5.2.1. Date/Time Operators</h4></div></div></div>

<p>日期时间的偏移计算</p>

select now() + interval '3 day';

select now() - interval '3 day';

select now() + interval '1 hour';

select now() - interval '1 hour';

select now() + interval '10 minutes';

select now() - interval '10 minutes';

select now() + interval '5 days 3 hours';

select now() + interval '5 days' + interval '3 hours';

</pre>

</div>

<p>当前日期 current_date</p>

netkiller=> select current_date;

date

------------

2003-11-28

(1 row)

netkiller=>

</pre>

<p>当前时间 current_time</p>

netkiller=> select current_time;

timetz

--------------------

19:38:47.270235+08

(1 row)

netkiller=>

</pre>

<p>当前日期时间 current_timestamp</p>

netkiller=> select current_timestamp;

timestamptz

-------------------------------

2003-11-28 19:39:25.548505+08

(1 row)

netkiller=>

</pre>

1. current_timestamp::timestamp (0)

2. current_timestamp::timestamp (0) without time zone;

netkiller=> select current_timestamp::timestamp (0);

timestamp

---------------------

2003-11-28 19:44:33

(1 row)

netkiller=>

netkiller=> select current_timestamp::timestamp (0) without time zone;

timestamp

---------------------

2003-11-28 19:40:10

(1 row)

</pre>

select now();

</pre>

<p>clock_timestamp() 函数</p>

SELECT clock_timestamp();

</pre>

</div>

3.1.5 计算时间差

netkiller=> select to_date('2003-12-2','YYYY-MM-DD')-to_date('2003-12-1','YYYY-MM-DD');

?column?

----------

(1 row)

netkiller=>

netkiller=> select to_date('2003-12-2','YYYY-MM-DD')-to_date('2003-10-2','YYYY-MM-DD');

?column?

----------

(1 row)

3.1.6 计算时间和

netkiller=> select to_date('2003-12-6','yyyy-mm-dd')+12 ;

?column?

------------

2003-12-18

(1 row)

netkiller=> select to_date('2003-12-6','yyyy-mm-dd')+20 ;

?column?

------------

2003-12-26

(1 row)

</pre>

</div>

select count(*) as c, to_char(ctime, 'yyyy-mm') as dt from practice group by dt order by dt;

select count(*) as c, to_char(ctime, 'yyyy-mm-dd') as dt from practice group by dt order by dt;

select count(*) as c, to_char(ctime, 'yyyy-mm-dd hh') as dt from practice group by dt order by dt;

</pre>

</div>

<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idp53"></a>7.5.2.5. EXTRACT, date_part</h4></div></div></div>

select extract (year from now());

select extract (month from now());

select extract (day from now());

select extract (day from timestamp '2013-06-03');

select extract (hour from now());

select extract (minute from now());

select extract (second from now());

select extract (week from now());

SELECT extract(century FROM now());

</pre>

3.1.7 date_part

netkiller=> select date_part('epoch', '2003-12-3 10:20:30' - timestamp '2003-12-1 02:00:00') ;

date_part

-----------

202830

(1 row)

netkiller=> select date_part('day', '2003-12-3 10:20:30' - timestamp '2003-12-1 02:00:00') ;

date_part

-----------

(1 row)

netkiller=> select date_part('hour', '2003-12-3 10:20:30' - timestamp '2003-12-1 02:00:00') ;

date_part

-----------

(1 row)

netkiller=>

</pre>

</div>

<div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idp54"></a>7.5.2.6. date_trunc</h4></div></div></div>

<p></p>

select count(*) as c, date_trunc('day', ctime) as dt from practice group by dt;

</pre>

</div>

<p>pg_sleep(seconds)</p>

SELECT pg_sleep(1.5);

</pre>

</div>

SELECT now() AT TIME ZONE 'GMT';

SELECT now() AT TIME ZONE 'GMT+8';

</pre>

show time zone;

US/Pacific

</pre>

set time zone 'PRC';

</pre>

<p>永久生效到pgdata下的postgresql.conf配置里修改两项</p>

log_timezone = 'PRC'

timezone = 'PRC'

</pre>

</div>

create extension "uuid-ossp";

create table products (product_id uuid primary key default uuid_generate_v4());

</pre>

</div>

<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="tablefunc"></a>7.5.4. tablefunc</h3></div><div><h4 class="subtitle">http://www.postgresql.org/docs/9.1/static/tablefunc.html</h4></div></div></div>

<p>确认扩展是否已经安装</p>

$ ls -1 /usr/pgsql-9.3/share/extension/tablefunc*

/usr/pgsql-9.3/share/extension/tablefunc--1.0.sql

/usr/pgsql-9.3/share/extension/tablefunc.control

/usr/pgsql-9.3/share/extension/tablefunc--unpackaged--1.0.sql

</pre>

$ psql test

psql (9.3.1)

Type "help" for help.

test=# create extension tablefunc;

CREATE EXTENSION

test=# \q

</pre>

<p>数据库结构</p>

-- Table: account

-- DROP TABLE account;

CREATE TABLE account

(

id SERIAL NOT NULL,

name character varying(10) NOT NULL, -- 账号

balance money NOT NULL DEFAULT 0.00, -- 余额

datetime timestamp without time zone NOT NULL DEFAULT (now())::timestamp(0) without time zone,

CONSTRAINT account_pkey PRIMARY KEY (id)

)

WITH (

OIDS=FALSE

);

ALTER TABLE account

OWNER TO dba;

COMMENT ON COLUMN account.name IS '账号';

COMMENT ON COLUMN account.balance IS '余额';

-- Index: account_name_idx

-- DROP INDEX account_name_idx;

CREATE INDEX account_name_idx

ON account

USING btree

(name COLLATE pg_catalog."default");

</pre>

INSERT INTO account (id, name, balance, datetime) VALUES (1, 'Neo', '$0.00', '2013-10-09 10:51:10');

INSERT INTO account (id, name, balance, datetime) VALUES (2, 'Neo', '$12.60', '2013-10-09 10:51:22');

INSERT INTO account (id, name, balance, datetime) VALUES (3, 'Neo', '$200.00', '2013-10-09 10:11:52');

INSERT INTO account (id, name, balance, datetime) VALUES (4, 'Neo', '-$6.80', '2013-10-09 10:51:42');

INSERT INTO account (id, name, balance, datetime) VALUES (5, 'Neo', '$100.00', '2013-10-09 10:52:49');

INSERT INTO account (id, name, balance, datetime) VALUES (6, 'Jerry', '$200.00', '2013-10-09 10:56:35');

INSERT INTO account (id, name, balance, datetime) VALUES (7, 'Jerry', '$50.45', '2013-10-09 10:57:23');

INSERT INTO account (id, name, balance, datetime) VALUES (8, 'Jerry', '$75.50', '2013-10-09 10:57:31');

INSERT INTO account (id, name, balance, datetime) VALUES (9, 'Jerry', '-$55.30', '2013-10-09 10:59:28');

INSERT INTO account (id, name, balance, datetime) VALUES (10, 'Jerry', '-$200.00', '2013-10-09 10:59:44');

INSERT INTO account (id, name, balance, datetime) VALUES (11, 'Tom', '$5.00', '2013-10-15 13:26:19');

INSERT INTO account (id, name, balance, datetime) VALUES (12, 'Neo', '$50.60', '2013-10-15 13:26:34');

INSERT INTO account (id, name, balance, datetime) VALUES (13, 'Jerry', '$62.08', '2013-10-15 13:26:51');

INSERT INTO account (id, name, balance, datetime) VALUES (14, 'Tom', '$70.00', '2013-10-15 13:27:01');

INSERT INTO account (id, name, balance, datetime) VALUES (15, 'Neo', '-$20.56', '2013-10-15 13:27:19');

INSERT INTO account (id, name, balance, datetime) VALUES (16, 'Tom', '$70.00', '2013-10-16 13:27:01');

INSERT INTO account (id, name, balance, datetime) VALUES (17, 'Jerry', '$70.00', '2013-10-16 13:27:01');

INSERT INTO account (id, name, balance, datetime) VALUES (18, 'Jerry', '-$30.00', '2013-10-16 13:30:01');

INSERT INTO account (id, name, balance, datetime) VALUES (19, 'Neo', '-$30.00', '2013-10-16 13:35:01');

INSERT INTO account (id, name, balance, datetime) VALUES (20, 'Tom', '-$30.00', '2013-10-16 13:35:01');

</pre>

SELECT * FROM crosstab('select datetime,name,balance from account order by 1,2','select name from account group by name order by 1') AS account(datetime timestamp, Jerry character varying, Neo character varying, Tom character varying);

</pre>

datetime | jerry | neo | tom

---------------------+----------+---------+---------

2013-10-09 10:11:52 | | $200.00 |

2013-10-09 10:51:10 | | $0.00 |

2013-10-09 10:51:22 | | $12.60 |

2013-10-09 10:51:42 | | -$6.80 |

2013-10-09 10:52:49 | | $100.00 |

2013-10-09 10:56:35 | $200.00 | |

2013-10-09 10:57:23 | $50.45 | |

2013-10-09 10:57:31 | $75.50 | |

2013-10-09 10:59:28 | -$55.30 | |

2013-10-09 10:59:44 | -$200.00 | |

2013-10-15 13:26:19 | | | $5.00

2013-10-15 13:26:34 | | $50.60 |

2013-10-15 13:26:51 | $62.08 | |

2013-10-15 13:27:01 | | | $70.00

2013-10-15 13:27:19 | | -$20.56 |

2013-10-16 13:27:01 | $70.00 | | $70.00

2013-10-16 13:30:01 | -$30.00 | |

2013-10-16 13:35:01 | | -$30.00 | -$30.00

(18 rows)

</pre>

</div>

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