Introduction to or syntax in sql

1. The use of or syntax in mysql, points to note when using or in mysql syntax.

  $sql = 'SELECT 
                * 
            FROM 
                `vvt_spread_doubleegg_exchange_award` AS p
            WHERE
                p.`act_type` = 4 or p.`act_type` = 5
            AND
                p.`user_id` = ' .$user_id
            ;

The or syntax in sql is generally used for queries with multiple conditions. The above syntax query is equivalent to: two sql The queried data collection.

<span style="color: #000000">  $sql = &#39;SELECT *  FROM  `vvt_spread_doubleegg_exchange_award` AS p WHERE  p.`act_type` = 4;<br/><span style="color: #000000">$sql = &#39;SELECT * FROM `vvt_spread_doubleegg_exchange_award` AS p WHERE  <span style="color: #000000">p.`act_type` = 5 AND p.`user_id` = &#39; .$user_id</span>;</span></span>

2. If you want to query the data set of act_type = 4 and user_id = 11123 or equal to p.`act_type` = 5 and user_id = 11123 or both sides The condition must be added ().

  $sql = 'SELECT 
                * 
            FROM 
                `vvt_spread_doubleegg_exchange_award` AS p
            WHERE
                （p.`act_type` = 4 or p.`act_type` = 5）
            AND
                p.`user_id` = ' .$user_id
            ;

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