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Using Ifnull in Subquery SQLite


Using Ifnull in Subquery SQLite

By : user2951459
Date : November 18 2020, 11:13 AM
like below fixes the issue I've this two tables, members and water_meter , You haven't assigned correct where condition in inner query.
code :
SELECT m.id, m.name, 
  ifnull(t.start,
         (SELECT ifnull(finish, 0) FROM members m2 
          LEFT JOIN water_meter t2
            ON m2.id = t2.member_id AND t2.date = '2014-07-01'
          where m2.id = m.id)) as start, 
  t.finish, paid
FROM members m 
LEFT JOIN water_meter t ON m.id = t.member_id AND t.date = '2014-08-01'
WHERE m.active = 1
select
  members.id,
  name,
  coalesce(wm_cur.start, wm_prev.finish),
  wm_cur.finish
from members
left join water_meter wm_cur
  on members.id = wm_cur.member_id
    and wm_cur.date between '2014-08-01' and date('2014-08-01','start of month','+1 month','-1 day')
left join water_meter wm_prev
  on members.id = wm_prev.member_id
    and wm_prev.date between '2014-07-01' and date('2014-07-01','start of month','+1 month','-1 day')
where members.active = 1


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SQLite equivalent to ISNULL(), NVL(), IFNULL() or COALESCE()

SQLite equivalent to ISNULL(), NVL(), IFNULL() or COALESCE()


By : reinhat
Date : March 29 2020, 07:55 AM
it helps some times IFNULL, see here: http://www.sqlite.org/lang_corefunc.html#ifnull
no brackets around the function
SQLite `ifnull()` vs `coalesce()` performance

SQLite `ifnull()` vs `coalesce()` performance


By : Martin
Date : March 29 2020, 07:55 AM
Hope this helps I have confirmed Gordon Linoff's statement with some experiments. Setup: SQLiteSpy on Windows 8, i5 and the whole table in RAM.
Either query took about 1.64 secs with very small fluctuations (less than .1 sec). Most of the time they were right on 1.64 secs.
code :
    create table t (
      a int, b int);

    insert into t values (null,null);
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;
    insert into t select case when random() < .5 then 1 end, case when random() < .5 then 1 end from t;

    select sum(ifnull(a, b)) from t;
    select sum(coalesce(a, b)) from t;
    select count(*) from t;
Ifnull on subquery returns...NULL

Ifnull on subquery returns...NULL


By : Chethan Srinivas
Date : March 29 2020, 07:55 AM
should help you out Any ideas why this subquery returns NULL when I'm expecting a 0 on NULL values: , This should be used on the outer query..
code :
SELECT
  ifnull((SELECT ifnull(visit.timestamp, 0) AS ifnull_1
   FROM keyword
   WHERE visit.keyword_id = keyword.id
   ORDER BY visit.timestamp DESC LIMIT 1), 0) AS keyword_last_visit
FROM keyword
LEFT OUTER JOIN visit ON visit.keyword_id = keyword.id
Will using IFNULL prevent SQLite from using an index?

Will using IFNULL prevent SQLite from using an index?


By : iamwkp
Date : March 29 2020, 07:55 AM
this one helps. It will result in a table scan.
Example using the sqlite3 command line client:
code :
sqlite> create table t(f);
sqlite> create index tf on t(f);
sqlite> explain query plan select * from t where ifnull(f,0)=1;
0|0|0|SCAN TABLE t (~500000 rows)
sqlite> explain query plan select * from t where f is null;
0|0|0|SEARCH TABLE t USING COVERING INDEX tf (f=?) (~10 rows)
sqlite> explain query plan select * from t where f=1;
0|0|0|SEARCH TABLE t USING COVERING INDEX tf (f=?) (~10 rows)
sqlite IFNULL() in postgres

sqlite IFNULL() in postgres


By : Twingo
Date : March 29 2020, 07:55 AM
may help you . try coalesce:
code :
SELECT coalesce(max(code_id) + 1, 1) 
FROM configentries 
WHERE configtable_id = ...
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