POSTGIS杂记

查询记录数

SELECT Count(*) FROM siteaddresses;

多字段查询||表示连字符

SELECT siteaddres || ' ' || city || ' ' || zipcode AS str
  FROM siteaddresses
  LIMIT 100;
--首字母大写
SELECT
  initcap(siteaddres || ', ' || city) AS address,
  ts_rank_cd(ts, query) AS rank
FROM siteaddresses

字符操作
操作符：
“~” Matches regular expression, case sensitive
“~*” Matches regular expression, case insensitive

SELECT array_to_string(regexp_split_to_array('the quick brown fox jumps over the lazy dog', E'\\s+'),'&');
--结果
--the&quick&brown&fox&jumps&over&the&lazy&dog

regexp_split_to_array函数 用空格（正则表达式\s）分割字符串
array_to_string函数将分割后用&连接

全文检索
PostgreSQL’s full-text search includes a number of useful features:

• Matching partial words（局部词组匹配）.
• Ranking results based on match quality（检索结果排序）.
• Synonym dictionaries.（同义词典）

-- Add a column for the text search data
ALTER TABLE siteaddresses ADD COLUMN ts tsvector;

-- Populate text search column by joining together relevant fields
-- into a single string
UPDATE siteaddresses
  SET ts  = to_tsvector('simple', siteaddres || ' ' || city || ' ' || zipcode)
  WHERE siteaddres IS NOT NULL;

PostgreSQL allows text search queries to be logically structured so that they search out documents that include all words, any words, or a combination of those conditions using and (&) and or (|) clauses.

Find all the records with “120 CINDY CT” in them:

SELECT siteaddres, city
FROM siteaddresses
WHERE ts @@ to_tsquery('simple','120 & CINDY & CT');

‘@@’操作符在这里返回boolean类型，判断tsvector 与 tsquery 是否匹配
‘simple’参数，在处理文本时采用的字典，针对不同语言有对应字典，可以实现诸如去除虚词、同义检索等，这里“simple”参数表示只是单纯的去除空格和标点符号。

通过”:*”后缀实现局部匹配
比如匹配包含120 和 以CI（i）开始的的内容

SELECT siteaddres, city
FROM siteaddresses
WHERE ts @@ to_tsquery('simple','120 & CI:*');

ts_rank_cd() 函数可以计算匹配程度并给定权重，按匹配程度排序：

SELECT
  siteaddres,
  city,
  ts_rank_cd(ts, query) AS rank
FROM siteaddresses,
     to_tsquery('simple','120 & CI:*') AS query
WHERE ts @@ query
ORDER BY rank DESC
LIMIT 10;

对siteaddres和city进行包装（合并显示，首字母大写）使显示更漂亮：

SELECT
  initcap(siteaddres || ', ' || city) AS address,
  ts_rank_cd(ts, query) AS rank
FROM siteaddresses,
     to_tsquery('simple','120 & CI:*') AS query
WHERE ts @@ query
ORDER BY rank DESC;

考虑到交互方便，用函数实现自动生成匹配表达式，比如输入“120 CI”自动生成上述表达式“120 & CI:*”：

-- An SQL function to wrap up the pre-processing step that takes
-- an unformated query string and converts it to a tsquery for
-- use in the full-text search
--xx ~ ' $' 表示匹配以空格结尾的字符串
CREATE OR REPLACE FUNCTION to_tsquery_partial(text)
  RETURNS tsquery AS $$
    SELECT to_tsquery('simple',
           array_to_string(
           regexp_split_to_array(
           trim($1),E'\\s+'),' & ') ||
           CASE WHEN $1 ~ ' $' THEN '' ELSE ':*' END)
  $$ LANGUAGE 'sql';

-- Input:  100 old high
-- Output: 100 & old & high:*
SELECT to_tsquery_partial('100 old high');

--用函数替换后的表达式最终如下
--在geoserver中建立SQL表，实现输入检索文本，返回匹配内容
SELECT
  initcap(a.siteaddres || ', ' || city) AS address,
  a.gid AS gid,
  ts_rank_cd(a.ts, query) AS rank
FROM siteaddresses AS a,
     to_tsquery_partial('100 old high') AS query
WHERE ts @@ query
ORDER BY rank DESC
LIMIT 10;