Re: Too slow query, do you have an idea to optimize?

Generate them all into a table and just delete them as you use them.
It's only 10000 rows...

Chris

Choe, Cheng-Dae wrote:
> I need to generate unused random id with format is ID[0-9]{4}
> so i write below query but it seems to be too slow
>
> SELECT * FROM (
> SELECT user_id FROM (
> SELECT 'ID' || LPAD(r, 4, '0') AS user_id
> FROM generate_series(1, 9999) as r) AS s
> EXCEPT
> SELECT user_id FROM account ) AS t
> ORDER BY random()
> LIMIT 1
>
> and I execute explain analyze query.
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Limit (cost=318.17..318.17 rows=1 width=32) (actual
> time=731.703..731.707 rows=1 loops=1)
> -> Sort (cost=318.17..318.95 rows=312 width=32) (actual
> time=731.693..731.693 rows=1 loops=1)
> Sort Key: random()
> -> Subquery Scan t (cost=285.79..305.24 rows=312 width=32)
> (actual time=424.299..659.193 rows=9999 loops=1)
> -> SetOp Except (cost=285.79..301.35 rows=311
> width=16) (actual time=424.266..566.254 rows=9999 loops=1)
> -> Sort (cost=285.79..293.57 rows=3112
> width=16) (actual time=424.139..470.529 rows=12111 loops=1)
> Sort Key: user_id
> -> Append (cost=0.00..105.24 rows=3112
> width=16) (actual time=5.572..276.485 rows=12111 loops=1)
> -> Subquery Scan "*SELECT* 1"
> (cost=0.00..30.00 rows=1000 width=4) (actual time=5.565..149.615
> rows=9999 loops=1)
> -> Function Scan on
> generate_series r (cost=0.00..20.00 rows=1000 width=4) (actual
> time=5.553..63.224 rows=9999 loops=1)
> -> Subquery Scan "*SELECT* 2"
> (cost=0.00..75.24 rows=2112 width=16) (actual time=0.030..28.473
> rows=2112 loops=1)
> -> Seq Scan on account
> (cost=0.00..54.12 rows=2112 width=16) (actual time=0.019..10.155
> rows=2112 loops=1)
> Total runtime: 738.809 ms
>
>
> do you have any idea for optimize?