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MySQL Dual table Join Dual table


MySQL Dual table Join Dual table

By : BrettH
Date : November 22 2020, 10:31 AM
wish help you to fix your issue Is there a way to JOIN fields from the dummy DUAL table in MySQL? , Here's one way...
code :
Select t1.n1, t2.n2 
from (select 1 as n1) t1 
CROSS JOIN (Select 2 as n2) t2;
Select t1.n1, t2.n2 
from (select 1 as n1, 'A' as ID) t1 
INNER JOIN (Select 2 as n2, 'A' as ID) t2
  on T1.Id = T2.ID;
Select 1 as n1, 2 as n2


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MySQL Partitioning Join Table (Dual PK)

MySQL Partitioning Join Table (Dual PK)


By : Kimiyoshi Hosoi
Date : March 29 2020, 07:55 AM
To fix the issue you can do Problem was the dual primary key. As a dual, it basically had to look at every record in the join table. I added a single key for tag_id and a single key for image_id and it drastically improved the speed. Machavity!
Mysql count, join, and dual in conjunction

Mysql count, join, and dual in conjunction


By : Yaroslav
Date : March 29 2020, 07:55 AM
I wish did fix the issue. I have a table tester which has a primary id and a foreign key that references the id of a table called test. , I would write your query like this:
code :
INSERT INTO tester (test, createddate, ipaddress) 
SELECT
  test.ID, NOW(), 'xxx.xxx.xxx.xxx'
FROM
  test
WHERE
  test.ID = 1
  AND EXISTS (SELECT COUNT(*)
              FROM tester
              WHERE tester.test = test.ID
              HAVING test.numAllowed-COUNT(*)>0);
MySQL insert multiple rows into empty table using SELECT FROM DUAL WHERE NOT EXISTS

MySQL insert multiple rows into empty table using SELECT FROM DUAL WHERE NOT EXISTS


By : user3564594
Date : March 29 2020, 07:55 AM
will be helpful for those in need I am using this code to insert a default row if the table is definitely empty. I am trying to extend this to insert multiple rows but cannot figure out the syntax: , Something like this should work:
code :
CREATE TEMPORARY TABLE `myDefaults` ( the_value INT|VARCHAR|whatever... )
;
INSERT INTO myDefaults (the_value) VALUES (myVal1), (myVal2), ....
;

SET @valCount := 0; -- Because I am paranoid ;)
SELECT COUNT(1) INTO @valCount FROM myTable;

INSERT INTO myTable(myCol)
SELECT the_value 
FROM myDefaults 
WHERE @valCount = 0
;

DROP TEMPORARY TABLE `myDefaults`;
Inserting new id from sequence into table column id and insert that same id to another table without dual table

Inserting new id from sequence into table column id and insert that same id to another table without dual table


By : kajak
Date : March 29 2020, 07:55 AM
this one helps. I'm posting solution where I use kartica_seq as a sequence for kartica_id. Please replace it with your sequence name or create sequence if it not exist.
create sequence kartica_seq start with 1 increment by 1;
code :
create or replace procedure insertOsoba
   ( o_osoba_id in osoba.osoba_id%type default generate_id.nextval,
     o_ime_osobe in osoba.ime_osobe%type,
     o_prezime_osobe in osoba.prezime_osobe%type,
     o_kartica_id in kartica.kartica_id%type default null --must be optional
   )
is
cnt number;
cnt2 number;
begin
      select count(*) into cnt from osoba where kartica_id = o_kartica_id;
      select count(*) into cnt2 from kartica where kartica_id = o_kartica_id;
      if(cnt = 0) then
        --there is no person with such kartica and user passed existing kartica_id
        if(o_kartica_id is not null and cnt2 > 0) then
          insert into osoba (osoba_id,ime_osobe,prezime_osobe,kartica_id)
          values (o_osoba_id,o_ime_osobe,o_prezime_osobe,o_kartica_id);
        --there is no person with such kartica but we need to create one entry using sequence
        else
          insert into kartica (kartica_id) values (kartica_seq.nextval);
          insert into osoba (osoba_id,ime_osobe,prezime_osobe,kartica_id)
          values (o_osoba_id,o_ime_osobe,o_prezime_osobe,kartica_seq.currval);
        end if;
      end if;
      --there is person with such kartica
      if(cnt > 0) then
        dbms_output.put_line('Kartica_id already exists. No same values allowed.'); --or raise an exception here
      end if;
      commit;
end insertosoba;
Is it possible to include dual table in a join query

Is it possible to include dual table in a join query


By : MadGeek
Date : March 29 2020, 07:55 AM
Hope this helps One common use (for me) is to use it to make inline views to join on...
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