Hi everyone i'am new on codeigniter 4 and currently working on a small project in the project i'am trying to join three tables and display there data in single table.
Table_1
id unique_id Name
1 1111 Sam
2 2222 Charlote
Table_2
id unique_id Name
1 1212 Jhon
2 5151 Alex
Table_3
id author title
1 1111 Book_1
2 5151 Book_2
3 1111 Book_3
Result
------------------------
| No | Author | Title |
------------------------
| 1 | Sam | Book_1 |
| 2 | Alex | Book_2 |
| 3 | Sam | Book_3 |
------------------------
I've tried to join with, but not working.
$this->join('Table_1', 'Table_1.unique_id = Table_3.author ');
$this->join('Table_2', 'Table_2.unique_id = Table_3.author ');
$this->select('Table_1.Name');
$this->select('Table_2.Name');
$this->select('Table_3.*');
$this->orderBy('Table_3.id');
return $this->findAll();
Is there another way to Join them? Thank you
What you currently have won't work because your Table_1 and Table_2 are effectively the same table.
Taking your Attempt and correcting it to use LEFT JOIN
public function example_1() {
$this->join('Table_1', 'Table_1.unique_id = Table_3.author', 'LEFT');
$this->join('Table_2', 'Table_2.unique_id = Table_3.author', 'LEFT');
$this->select('Table_1.Name');
$this->select('Table_2.Name');
$this->select('Table_3.*');
$this->orderBy('Table_3.id');
$result = $this->findAll();
echo $this->db->getLastQuery();
return $result;
}
You would get...
SELECT `Table_1`.`Name`, `Table_2`.`Name`, `Table_3`.*
FROM `Table_3`
LEFT JOIN `Table_1` ON `Table_1`.`unique_id` = `Table_3`.`author`
LEFT JOIN `Table_2` ON `Table_2`.`unique_id` = `Table_3`.`author`
ORDER BY `Table_3`.`id`
array(3) {
[0]=>
array(4) {
["Name"]=>
NULL
["id"]=>
string(1) "1"
["author"]=>
string(4) "1111"
["title"]=>
string(6) "Book_1"
}
[1]=>
array(4) {
["Name"]=>
string(4) "Alex"
["id"]=>
string(1) "2"
["author"]=>
string(4) "5151"
["title"]=>
string(6) "Book_2"
}
[2]=>
array(4) {
["Name"]=>
NULL
["id"]=>
string(1) "3"
["author"]=>
string(4) "1111"
["title"]=>
string(6) "Book_3"
}
}
Note that you have, two occurrences of name in your query. So which one will win? It appears that Table_2.name is only used and any reference to Table_1.name is NULL as it's not used.
You could give them different names using aliases but then you would have something like name_1 and name_2 so which one is it? This is due to the duplication in your Table_1 and Table_2 and you asking for both.
The Better way So in this case you would need to perform an UNION on Table_1 and Table_2.
I don't think that there is a UNION command in the CI query builder.
Using mysql, it would be...
public function get_book_and_author() {
$sql = "SELECT Table_3.id, T12.name as author, Table_3.title
FROM (
SELECT Table_1.* FROM Table_1
UNION
SELECT Table_2.* FROM Table_2
) as T12
LEFT JOIN Table_3 ON T12.unique_id = Table_3.author
WHERE Table_3.author IS NOT NULL
";
$result = $this->db->query($sql);
return $result->getResultArray();
}
So in this example, we have specified the 3 fields you require in the Select. Note the T12.name is renamed author. (See the output below)
Then an UNION
has to be performed on Table_1 and Table_2 and the result is named (aliased) as T12 (shorthand for Table_1 and Table_2) as the result requires a new name.
Then a LEFT JOIN
is performed against Table_3, which will give all combinations where there will be NULLS, so the WHERE statement filters those out using "IS NOT NULL" on Table_3.author.
I left out the ORDER BY
as it's not really needed and you can add that back in if you wish to.
A var_dump() of the result gives...
array(3) {
[0]=>
array(3) {
["id"]=>
string(1) "1"
["author"]=>
string(3) "Sam"
["title"]=>
string(6) "Book_1"
}
[1]=>
array(3) {
["id"]=>
string(1) "2"
["author"]=>
string(4) "Alex"
["title"]=>
string(6) "Book_2"
}
[2]=>
array(3) {
["id"]=>
string(1) "3"
["author"]=>
string(3) "Sam"
["title"]=>
string(6) "Book_3"
}
}
So that will give you the id,author and title for each matching row as you have requested using your example Tables.
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