MySQL，CONCAT，一段时间后结果为null

问题描述：

我将大数据放入表中，并放入LONGBLOB字段中，但是随着表的增长，该字段变为空.代码:

Im putting big data to table, to a LONGBLOB field, but as the table grows, the field becomes empty. Code:

mysql_query ('CREATE TABLE IF NOT EXISTS testtable (content LONGBLOB NOT NULL) ENGINE = MyISAM');
mysql_query('TRUNCATE TABLE testtable');
mysql_query('REPLACE INTO testtable VALUES (".")');
$bigData = str_repeat('A', 1024*1024*2); // 2 MB!
foreach (str_split($bigData, 1024*64) as $item)
{
    mysql_query ('UPDATE testtable SET content = CONCAT(content, "'.mysql_real_escape_string($item).'")');
    $rec = mysql_fetch_row(mysql_query ('SELECT content FROM testtable'));
    echo 'Size of the content: '.strlen($rec[0]).'<br>';
}

输出:

Size of the content: 65537
Size of the content: 131073
Size of the content: 196609
Size of the content: 262145
Size of the content: 327681
Size of the content: 393217
Size of the content: 458753
Size of the content: 524289
Size of the content: 589825
Size of the content: 655361
Size of the content: 720897
Size of the content: 786433
Size of the content: 851969
Size of the content: 917505
Size of the content: 983041
Size of the content: 0
Size of the content: 65536
Size of the content: 131072
Size of the content: 196608

发生了什么事? LONGBLOB应该获取更多的数据.

Whats happening? LONGBLOB should take more data than that.

答

增大max_allowed_packet大小.

看起来好像失败了1MB，并且根据

It looks like it is failing at 1MB, and according to https://dev.mysql.com/doc/refman/5.5/en/packet-too-large.html the default max packet size is 1MB:

服务器的默认max_allowed_packet值为1MB.如果服务器需要处理大查询，则可以增加此值

The server's default max_allowed_packet value is 1MB. You can increase this if the server needs to handle big queries

在my.cnf文件中设置值，例如:

Set the value in the my.cnf file, e.g.:

[mysqld]
max_allowed_packet=16M

在PHP中

如果您无权访问MySQL配置，则可以尝试通过查询进行设置(注意:我尚未检查这是否可行).

In PHP

If you don't have access to the MySQL config you could try setting via a query (note: I've not checked if this will work).

$db->query( 'SET @@global.max_allowed_packet = 16777216' );

MySQL，CONCAT，一段时间后结果为null

在PHP中

In PHP

相关推荐