SQL将ORDER BY结果作为数组返回

Question

Is it possible to return groups as an associative array? I'd like to know if a pure SQL solution is possible. Note that I release that I could be making things more complex unnecessarily but this is mainly to give me an idea of the power of SQL.

My problem: I have a list of words in the database that should be sorted alphabetically and grouped into separate groups according to the first letter of the word.

For example:

ape
broom
coconut
banana
apple

should be returned as

array(
'a' => 'ape', 'apple',
'b' => 'banana', 'broom',
'c' => 'coconut'
)

so I can easily created sorted lists by first letter (ie clicking "A" only shows words starting with a, "B" with b, etc. This should make it easier for me to load everything in one query and make the sorted list JavaScript based, ie without having to reload the page (or use AJAX).

Side notes: I'm using PostgreSQL but a solution for MySQL would be fine too so I can try to port it to PostgreSQL. Scripting language is PHP.

Answer 1

MySQL:

SELECT LEFT(word, 1) AS first_letter, 
  GROUP_CONCAT(word) AS word_list
FROM MyTable
GROUP BY LEFT(word, 1);

PostgreSQL 8.4:

SELECT SUBSTRING(word FOR 1) AS first_letter, 
  ARRAY_TO_STRING(ARRAY_AGG(word), ',') AS word_list
FROM MyTable
GROUP BY SUBSTRING(word FOR 1);

See http://mssql-to-postgresql.blogspot.com/2007/12/cool-groupconcat.html for more about emulating MySQL's GROUP_CONCAT() in PostgreSQL.

See http://www.postgresonline.com/journal/index.php?/archives/126-PostgreSQL-8.4-Faster-array-building-with-array_agg.html for more on ARRAY_AGG() .

Answer 2

Run 26 separate queries. Or run one query and separate the results alphabetically server side.

Answer 3

Are you familiar with the LIKE syntax?

as in

SELECT * FROM words WHERE col LIKE a% ORDER BY col

would give you the a's in order and so on. Build the hash accordingly.

Answer 4

I'm no PostgreSQL expert (or user) but I believe in the later versions you can do something like this:

SELECT 
    ROW_NUMBER() OVER (PARTITION BY SUBSTRING(whatever from 1 for 1) ORDER BY whatever) AS __ROW,
    whatever
FROM yourtable;

This is ANSI SQL. I don't know what the support on MySql is like yet. Oracle and SQL Server both work with this syntax and I heard it through Google that PostgreSQL 8.4 supports windowing functions.