How to remove duplicate data when performing join query in thinkphp

In the ThinkPHP framework, we often need to perform multi-table association queries, among which join query is a common method. However, in multi-table related queries, if no processing is done, duplicate data is likely to occur. This article will introduce how to remove duplicate data when performing join queries in ThinkPHP.

1. Problem Analysis

When performing multi-table related queries, we usually use the following code:

$model = M('table1');
$data = $model->join('table2 ON table1.id=table2.table1_id')
              ->field('table1.*, table2.*')
              ->select();

In the above code, we The join method is used to perform associated queries between the two tables, and then the field method is used to specify the fields to be queried.

However, since the data in the two tables is duplicated, duplicate data will also appear in the query results. For example, the results of our query may be similar to the following:

id   | name  | age   | table1_id | content
-----------------------------------------
1    | John  | 20    | 1         | ...
2    | Mary  | 22    | 2         | ...
3    | John  | 20    | 3         | ...
4    | Bruce | 25    | 1         | ...
5    | Mary  | 22    | 5         | ...

As you can see, there are two pieces of data that are duplicated, namely the two pieces of data with IDs 1 and 3. This is because they are both related to The data in table2 is related.

2. Deduplication processing

In order to remove duplicate data, we can use the DISTINCT keyword in MySQL, for example:

$model = M('table1');
$data = $model->distinct(true)
              ->join('table2 ON table1.id=table2.table1_id')
              ->field('table1.*, table2.*')
              ->select();

In the above code , we called the distinct(true) method, which will remove duplicate data from the search results, thereby obtaining the non-duplicate data we want.

At the same time, we can also use the group method to remove duplicates. For example:

$model = M('table1');
$data = $model->join('table2 ON table1.id=table2.table1_id')
              ->group('table1.id')
              ->field('table1.*, table2.*')
              ->select();

In the above code, we call the group('table1.id') method, which will group the query results according to the id field in the table1 table to obtain non-duplicate data .

3. Summary

This article introduces how to remove duplicates when performing join queries in ThinkPHP, including using the distinct and group methods. These methods are very commonly used, especially when performing complex multi-table related queries. At the same time, we also need to note that using these methods requires a certain amount of time and computing resources.

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