What is the use of "where 1=1" in SQL?

The use of where 1=1 in SQL

Explanation:

In fact, 1=1 is eternally true and means unconditional. That is to say, it does not matter whether there is 1=1 in the SQL statement.

This 1=1 is often used when applications piece together where conditions based on different user selections.

For example: the web interface queries user information, where defaults to 1=1, so that even if the user does not select any conditions, the SQL query will not go wrong. If the user selects a name, then where becomes where 1=1 and name=‘the name entered by the user’. If other conditions are selected, just keep appending and statements after the where condition.

If you don’t use 1=1, every time you add a condition, you have to judge whether there is a where condition in front of it. If not, write where..., if there is, write an and statement, so using 1=1 at this time can simplify it. Application complexity.

Example:

If the following code first defines $where= '1=1', then there is no need to judge whether $where

public function listAction()
    {
       $get = $this->getQuery();
        $statementBalanceDetailModel = M('Ticket\StatementBalanceDetail');

        $page = isset($get['page']) ? intval($get['page']) : 1;
        $pageSize = isset($get['page_size']) ? intval($get['page_size']) : 10;

        //用处
        $where = ' 1=1 ';
        $binds = array();
        if (isset($get['id']) && $get['id'] != '') {
            $where .= ' and id = :id';
            $binds['id'] = trim($get['id']);
        }

        if (isset($get['shop_name']) && $get['shop_name'] != '') {
            $where .= ' and shop_name = :shop_name';
            $binds['shop_name'] = trim($get['shop_name']);
        }

        if (isset($get['statement_sn']) && $get['statement_sn'] != '') {
            $where .= ' and statement_sn = :statement_sn';
            $binds['statement_sn'] = trim($get['statement_sn']);
        }

        $where .= ' order by id desc';
        $result = $statementBalanceDetailModel->paginate($where, $pageSize, $page, $fields = array(), $binds);
        $sceneryList = $result['data'];
        $total = $result['total_result'];
        $pager = Paginate::web($total, $page, $pageSize);

        $data = array(
            'pager' => $pager,
            'sceneryList' => $sceneryList,
        );

        $this->getView()->assign($data);
    }

## exists. # This article is reproduced from: https://blog.csdn.net/longgeaisisi/article/details/100599010

Recommended learning:

mysql tutorial

The above is the detailed content of What is the use of "where 1=1" in SQL?. For more information, please follow other related articles on the PHP Chinese website!