Codeigniter - 加入派生表 [英] Codeigniter - Joining derived tables

问题描述

我知道如何加入2个基本表。我想知道的是如何通过向 mysql 中添加别名来连接 Codeigniter 中的派生表。

I know how to join 2 basic tables. What I'm interested in knowing is how do I join the derived tables in Codeigniter like we do in mysql by giving aliases to the tables.

例如：

Table1->where(something)->group_by(something) as derived_table1

Table2->where(something AND something)->group_by(something) as derived_table2

如何离开加入这两个表格？

em>请注意：我知道我可以先加入，然后应用where子句。但这会更改查询结果。我需要离开连接派生表。

Please note: I know I can left join first and then apply the where clauses. But that changes the query result. I need to left join the derived tables.

推荐答案

我不知道这是规范的方法，但这是我如何做的例子：

i'm not sure that this is the canonical approach, but this is example how i do it:

// Build subquery
$this->db->select('max(a) a', false);
$this->db->group_by('b');
// Save subquery
$subQuery =  $this->db->get_compiled_select('table-1');

// Main query
$this->db->select('t.a', false);
$this->db->from('table-2'); 
// Here insert subquery
$this->db->join("($subQuery) t", 'condition', 'left');
$query = $this->db->get();

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