为什么不是'；我的查询是否使用绑定参数插入?但是它使用相同的bind_param进行更新

我在使用bind_param执行DB插入时遇到问题，但我可以使用相同的bind_param方法进行更新，但无法插入。这里是我的更新(有效的(和插入(无效的(函数。

function update()
{
    $query = "
        UPDATE " . $this->table_name . "
           SET category_key= :ck,
               product_name = :pn,
               unit_of_measurement = :uom,
               price = :pc,
               pieces = :ps,
               last_date_added = :lda,
               last_added_by = :lab,
               reorder = :rd,
               note = :no
         WHERE product_key LIKE :pk
    ";
    $stmt = $this->conn->prepare($query);
    $stmt->bindParam(':ck', $this->category_key);
    $stmt->bindParam(':pn', $this->product_name);
    $stmt->bindParam(':uom', $this->unit_of_measurement);
    $stmt->bindParam(':pc', $this->price);
    $stmt->bindParam(':ps', $this->pieces);
    $stmt->bindParam(':lda', $this->last_date_added);
    $stmt->bindParam(':lab', $this->last_added_by);
    $stmt->bindParam(':no', $this->note);
    $stmt->bindParam(':pk', $this->product_key);
    $stmt->bindParam(':rd', $this->reorder);
    // execute the query
    if ($stmt->execute()) {
        return true;
    } else {
        return false;
    }
}

function insert()
{
   $query = "
       INSERT INTO product_entry (
              category_key,
              product_key,
              product_name,
              unit_of_measurement,
              price,
              pieces,
              date_added,
              added_by,
              exp_date,
              store_key,
              branch_code,
              note
       ) 
       VALUES (
              :ck,
              :pk,
              :pn,
              :uom,
              :pc,
              :ps,
              :lda,
              :lab,
              :ep,
              :sk,
              :bc,
              :no
    )";
    $stmt = $this->conn->prepare($query);
    $stmt->bindParam(':sk', $this->store_key);
    $stmt->bindParam(':bc', $this->branch_code);
    $stmt->bindParam(':ck', $this->category_key);
    $stmt->bindParam(':pn', $this->product_name);
    $stmt->bindParam(':uom', $this->unit_of_measurement);
    $stmt->bindParam(':pc', $this->price);
    $stmt->bindParam(':ps', $this->pieces);
    $stmt->bindParam(':lda', $this->last_date_added);
    $stmt->bindParam(':lab', $this->last_added_by);
    $stmt->bindParam(':no', $this->note);
    $stmt->bindParam(':pk', $this->product_key);
    $stmt->bindParam(':ep', $this->exp_date);
    // execute the query
    if ($stmt->execute()) {
        return true;
    } else {
        return false;
    }
}

这是我的HTML表单，只是为了防止

<form method="post">    

<div class="form-group">
<input type="hidden" class="form-control" id="sk" name="store_key" value='<?php echo $product->store_key; ?>'>
<input type="hidden" class="form-control" id="bc" name="branch_code" value='<?php echo $product->branch_code; ?>'>
<label for="pn">Product Name</label>
<input type="text" class="form-control" id="pn" name="product_name" value='<?php echo $product->product_name; ?>'>
</div>
<div class="form-group">
    <label for="ms">Measurement</label>
    <input type="text" class="form-control" id="uom" name="unit_of_measurement" value='<?php echo $product->unit_of_measurement; ?>'>
</div>
<div class="form-group">
    <label for="qn">Price</label>
    <input type="text" class="form-control" rows="3" id="pc" name="price" value='<?php echo $product->price; ?>'/>
</div>
<div class="form-group">
    <label for="ps">Pieces</label>
    <input type="text" class="form-control" id="ps" name="pieces" value='<?php echo $product->pieces; ?>'/>
</div>
<div class="form-group">
    <label for="rd">Re-order</label>
    <input type="text" class="form-control" id="rd" name="reorder" value='<?php echo $product->reoder; ?>'/>
</div>
<div class="form-group">
    <label for="ep">Expiry Date</label>
    <input type="date" class="form-control" id="ep" name="exp_date" value='<?php echo $product->exp_date; ?>'/>
</div>
<div class="form-group">
    <label for="ab">Added By</label>
    <input type="text" class="form-control" id="lab" name="last_added_by" value='<?php echo $product->last_added_by; ?>'/>
</div>`
<div class="form-group">
    <label for="no">Note</label>
    <textarea class="form-control" rows="3" id="no" name="note"><?php echo $product->note; ?></textarea>
</div>
<button type="submit" name="submit" class="btn btn-success">Submit</button>
</form>

请注意，update和insert都是从同一个类调用的，并且是从相同的表单和php页面执行的，该页面更新产品表(有效(，但不插入到product_entry表中。