get the array value?

On Thu, Dec 25, 2008 at 7:15 AM, Charles.Hou <ivan.hou@msa.hinet.net> wrote:

name[] = { JOHN , ALEX , TEST ,""}

SQL : select name from table1 where 'TEST' = any (name)

return: { JOHN , ALEX , TEST }

in this sql command, how can i get the index of 'TEST' is 3 ?

First of all. I assume the code above is meant to be pseudo-code, otherwise
this makes not much sense to me.

But if I understand you correctly, that you want to find the index (or position)
of a specific item in an array, then you have to write a function that iterates
over the array and returns the index.

This is a bad design however and it doesn't scale up well with large arrays.

A better approach is storing the array elements as rows in a table with an
index, which can be queried more efficiently.

For example:

CREATE TABLE records (
id SERIAL PRIMARY KEY
);

CREATE TABLE names (
record_id INTEGER REFERENCES records,
position INTEGER NOT NULL,
name TEXT NOT NULL,
UNIQUE (record_id, position)
);

This way you can easily search by doing something like

SELECT position FROM names
WHERE name = 'TEST';

Regards,
Victor Nawothnig

2008/12/25 Victor Nawothnig <victor.nawothnig@gmail.com>:

On Thu, Dec 25, 2008 at 7:15 AM, Charles.Hou <ivan.hou@msa.hinet.net> wrote:

name[] = { JOHN , ALEX , TEST ,""}

SQL : select name from table1 where 'TEST' = any (name)

return: { JOHN , ALEX , TEST }

in this sql command, how can i get the index of 'TEST' is 3 ?

First of all. I assume the code above is meant to be pseudo-code, otherwise
this makes not much sense to me.

But if I understand you correctly, that you want to find the index (or position)
of a specific item in an array, then you have to write a function that iterates
over the array and returns the index.

This is a bad design however and it doesn't scale up well with large arrays.

A better approach is storing the array elements as rows in a table with an
index, which can be queried more efficiently.

For example:

CREATE TABLE records (
id SERIAL PRIMARY KEY
);

CREATE TABLE names (
record_id INTEGER REFERENCES records,
position INTEGER NOT NULL,
name TEXT NOT NULL,
UNIQUE (record_id, position)
);

This way you can easily search by doing something like

SELECT position FROM names
WHERE name = 'TEST';

Regards,
Victor Nawothnig

I absolutely agree with Victor, arrays doesn't supply normalization
(but in some cases arrays are very useful). You can write SQL function
IndexOf (for small arrays):

postgres=# create or replace function indexof(anyarray, anyelement)
returns integer as $$
select i
from
generate_series(array_lower($1,1),array_upper($1,1)) g(i)
where $1[i] = $2 limit 1;
$$ language sql immutable;
CREATE FUNCTION
postgres=# select indexof(array['Pavel','Jirka'],'Jirka');
indexof
---------
2
(1 row)

Regards
Pavel Stehule