我的iPhone应用程序连接到我的PHP web服务从MySQL数据库中检索数据,一个请求可以返回500个结果。

实现分页和一次检索20个项的最佳方法是什么?

假设我从数据库中接收了前20个条目,我现在如何请求接下来的20个条目?


当前回答

如果您希望在存储过程中执行此操作,可以尝试此操作

SELECT * FROM tbl limit 0, 20.

不幸的是,使用公式不起作用,所以你可以执行一个准备好的语句,或者只是给过程的开始和结束值。

其他回答

如果您希望在存储过程中执行此操作,可以尝试此操作

SELECT * FROM tbl limit 0, 20.

不幸的是,使用公式不起作用,所以你可以执行一个准备好的语句,或者只是给过程的开始和结束值。

查询1:SELECT * FROM yourtable WHERE id > 0 ORDER BY id LIMIT 500

查询2:SELECT * FROM tbl LIMIT 0,500;

查询1对中小记录运行更快,如果记录数量等于5000或更高,结果相似。

500条记录的结果:

Query1需要9.9999904632568毫秒

Query2耗时19.999980926514毫秒

8,000条记录的结果:

Query1需要129.99987602234毫秒

Query2需要160.00008583069毫秒

从MySQL文档:

The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must both be nonnegative integer constants (except when using prepared statements). With two arguments, the first argument specifies the offset of the first row to return, and the second specifies the maximum number of rows to return. The offset of the initial row is 0 (not 1): SELECT * FROM tbl LIMIT 5,10; # Retrieve rows 6-15 To retrieve all rows from a certain offset up to the end of the result set, you can use some large number for the second parameter. This statement retrieves all rows from the 96th row to the last: SELECT * FROM tbl LIMIT 95,18446744073709551615; With one argument, the value specifies the number of rows to return from the beginning of the result set: SELECT * FROM tbl LIMIT 5; # Retrieve first 5 rows In other words, LIMIT row_count is equivalent to LIMIT 0, row_count.

下面是我如何使用node.js和MySQL数据库解决这个问题。 首先,让我们声明变量!

    const 
        Key = payload.Key,
        NumberToShowPerPage = payload.NumberToShowPerPage,
        Offset = payload.PageNumber * NumberToShowPerPage;

NumberToShowPerPage是显而易见的,但是偏移量是页码。

现在SQL查询…

    pool.query("SELECT * FROM TableName WHERE Key = ? ORDER BY CreatedDate DESC LIMIT ? OFFSET ?", [Key, NumberToShowPerPage, Offset], (err, rows, fields) => {}));

我将把它分解一下。

Pool, is a pool of MySQL connections. It comes from mysql node package module. You can create a connection pool using mysql.createPool. The ?s are replaced by the variables in the array [PageKey, NumberToShow, Offset] in sequential order. This is done to prevent SQL injection. See at the end were the () => {} is? That's an arrow function. Whatever you want to do with the data, put that logic between the braces. Key = ? is something I'm using to select a certain foreign key. You would likely remove that if you don't use foreign key constraints.

希望这能有所帮助。

本教程展示了一种进行分页的好方法。 使用MySQL进行高效分页

简而言之,避免使用OFFSET或较大的LIMIT