PostgreSQL 9.4: UNNEST() WITH ORDINALITY to generate String Array Sequence Number

Anvesh Patel — Fri, 25 Nov 2016 15:35:32 +0000

PostgreSQL 9.4 introduced WITH ORDINALITY for generating a sequence number for each element which are produced by UNNEST().

When we are talking about the string array, internal element numbering is also important for further operation.

I have prepared a small demonstration of this, you can access here.

Create a table with sample data:

CREATE TABLE tbl_TextArray(key varchar(100), tags text[]);

INSERT INTO tbl_TextArray(key, tags)
VALUES 
('first', '{aa,fe,gr,fh}'::text[]),
('sec', '{tr,we,et,ui,er}'::text[]),
('third', '{we,gh,fv,dc,sx}'::text[]);

UNNEST() WITH ORDINALITY:

SELECT key, ArrayOrder, tag
FROM tbl_TextArray, unnest(tags) 
WITH ORDINALITY As T (tag, ArrayOrder);

The Result:

dbrnd=# SELECT key, ArrayOrder, tag
dbrnd-# FROM tbl_TextArray, unnest(tags)
dbrnd-# WITH ORDINALITY As T (tag, ArrayOrder);
  key  | arrayorder | tag
-------+------------+-----
 first |          1 | aa
 first |          2 | fe
 first |          3 | gr
 first |          4 | fh
 sec   |          1 | tr
 sec   |          2 | we
 sec   |          3 | et
 sec   |          4 | ui
 sec   |          5 | er
 third |          1 | we
 third |          2 | gh
 third |          3 | fv
 third |          4 | dc
 third |          5 | sx
(14 rows)

PostgreSQL XML Type

Anvesh Patel — Fri, 22 May 2015 15:53:55 +0000

In this post, I am sharing a demonstration on the XML data type of PostgreSQL.

Explain with the sample example.

What is XML Type ?

The XML Data type is used to store XML data. XML is well-formed storage structure of data. You can store multiple nodes into a single XML column. You can store data in hierarchical format.

E.g,

User preferences table, in which User can select multiple preferences and even User can create custom choices for them.

Now, how you can store this preferences data for those Users.

Simple, create one XML column and store all User preferences id into this. like,

124.

Below is a demonstration of XML with PostgreSQL.

Basically you can store XML data with one child node or with different child node.

Les’s First start with one child node:
Create table with XML type:

CREATE TABLE XMLTEST (Name XML);

Now Insert XML Data.

INSERT INTO XMLTEST 
VALUES
('
    
          _abc
          _xyz
          _pqr
          _cdf
   
');

Select data from XMLTEST:

SELECT *FROM XMLTEST

You can find above full XML into one column.

Now, time to parse this XML column using unnest() function of PostgreSQL.

SELECT unnest(xpath('.//Sub/text()', Name::xml))::text AS XMLDATA FROM XMLTEST;

Result is:

You can see this is four rows now, as we have stored different four values into one XML Column and after parse, we can see those four values in the form of different row.

Demonstration of different child node:

INSERT INTO XMLTEST VALUES
   ('
     
        Anvesh
        Hyderabad
        Male
        27
      
   ');

SELECT 
 unnest(xpath('//Name/text()', Name::XML)) AS Name
 ,unnest(xpath('//City/text()', Name::XML)) AS City
 ,unnest(xpath('//Gender/text()', Name::XML)) AS Gender
 ,unnest(xpath('//Age/text()', Name::XML)) AS Age
FROM XMLTEST;

Result is :

In the above code, we inserted an XML data with different child nodes.

You can see the result of one row with the various columns for the different child nodes.

unnest – Database Research & Development

PostgreSQL 9.4: UNNEST() WITH ORDINALITY to generate String Array Sequence Number

PostgreSQL XML Type