Set the cursor to be a scrollable cursor using the PDO::ATTR_CURSOR attribute
使用PDO::ATTR_CURSOR属性将游标设置为可滚动游标
In terms of performance, the forward-only cursor is better than the scrollable cursor.
而在性能方面，只能前进的游标优于可滚动游标。
However, in some cases, you will need to read cursors both forward and backward, in which case you should use scrollable cursor.
但某些情况下，您需要游标既能向前又能向后，此时需要使用可滚动游标。
Move your cursor inside the pop-up window, and the window becomes scrollable (see Figure 12).
把光标移到弹出窗口中，该窗口将变为可滚动窗口（参见图 12）。
A scrollable result set allows the cursor to be moved to any row in the result set.
可滚动结果集允许游标移动到结果集中的任意行。
Level 2 drivers do not need the cursor library because they are already scrollable.
级驱动程序不需要游标库，因为它们已是可滚动的。
Level 2 drivers do not need the cursor library because they are already scrollable.
级驱动程序不需要游标库，因为它们已是可滚动的。
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