Mysql 更新查询中的“（空白）where”和“where”有什么区别

Question

private function update($fields)
    {
      $query = 'UPDATE`'.$this->table.'`SET';
      foreach ($fields as $key => $value) {
        $query .= '`' . $key . '` = :'. $key . ',';
      }
      $query = rtrim($query, ',');
      $query .= ' WHERE `'. $this->primaryKey . '` = :primaryKey';
      $fields['primaryKey'] = $fields['id'];

      $fields = $this->processDates($fields);

      $this->query($query,$fields);
    }

I want to make the update method and these codes work. but when I change

$query .= ' WHERE `'. $this->primaryKey . '` = :primaryKey';

into

$query .= 'WHERE `'. $this->primaryKey . '` = :primaryKey';

, then it doesn't work. I guess the only difference is blank in front of WHERE.

I really don't understand why it doesn't work.

Answer 1

You are appending where clause to update query so without blank your update query is:

UPDATE tableName SET columnName = :placeholderWHERE primaryKey = :primaryKey;

With the blank:

UPDATE tableName SET columnName = :placeholder WHERE primaryKey = :primaryKey;

That is the difference.