mysqli中的位标志是什么意思使用fetch_field_direct [英] What do bit flags in mysqli mean using fetch_field_direct

问题描述

使用mysqli，我可以得到如下字段的信息：

Using mysqli, I can get information about fields like so

$field = mysqli_fetch_field_direct($result, $fieldCount);

，我可以使用

$field->flags

PHP手册说，这返回表示字段的位标志的整数。但这是所有的信息，我可以找到。如何解释位标志？到目前为止，我已经确定

The PHP manual says that this returns "An integer representing the bit-flags for the field." but that's all the info I can find. How can I interpret the bit flags? So far, I've worked out that

整数（字段长度无所谓）根据指定的属性返回以下位标志：

Integers (length of field doesn't matter) return the following bit flags depending on the attributes specified:

primary key 49967
primary & unique 53255
unique key 53251
foreign key 53257
unique & index 53259 (Auto increment 49675)

感谢您提供任何帮助！

推荐答案

请参阅 http://www.php.net/manual/en/mysqli-result.fetch-fields.php#101828

NOT_NULL_FLAG = 1                                                                             
PRI_KEY_FLAG = 2
UNIQUE_KEY_FLAG = 4                         
MULTIPLE_KEY_FLAG = 8
BLOB_FLAG = 16
UNSIGNED_FLAG = 32
ZEROFILL_FLAG = 64                    
BINARY_FLAG = 128                                       
ENUM_FLAG = 256
AUTO_INCREMENT_FLAG = 512
TIMESTAMP_FLAG = 1024
SET_FLAG = 2048
PART_KEY_FLAG = 16384
GROUP_FLAG = 32768
NUM_FLAG = 32768
UNIQUE_FLAG = 65536

上面公布的每个数是2的幂。（1 = 2 ^ 0,2 = 2 ^ 1，4 = 2 ^ 2等等）。换句话说，它们中的每一个对应于数字中的一个比特。要读取 49967 意味着您可以例如以二进制形式显示

Notice that every number posted above is a power of 2. (1 = 2^0, 2 = 2^1, 4 = 2^2 and so on). In other words, each of them corresponds to one bit in a number. To read what 49967 means, you can for example display it in binary form

>> decbin(49967);
'1100001100101111'

从右开始，您现在可以读取该字段有以下标志

Starting from right, you can now read that the field has following flags

NOT_NULL 
PRI_KEY  
UNIQUE_KEY
MULTIPLE_KEY
UNSIGNED
ENUM
AUTO_INCREMENT
GROUP
UNIQUE

其他方式检查specific flag is using binary conjunction operator & and mysqli constants as provided by nickb in below below：

Other way to check, for specific flag is using binary conjunction operator & and mysqli constants as provided by nickb in comment below:

>> echo MYSQLI_NOT_NULL_FLAG & 49967
1
>> echo MYSQLI_PRI_KEY_FLAG & 49967
2
>> echo MYSQLI_UNIQUE_KEY_FLAG & 49967
4
>> echo MYSQLI_MULTIPLE_KEY_FLAG & 49967
8
>> echo MYSQLI_BLOB_FLAG & 49967
0

基本上，您设置的标志的非零值，对于未设置的标志。您可以在这种情况下安全使用它：

Basically you gat non-zero value for flags that are set, and 0 for flags that are unset. You can safely use it in conditions like this:

if($fieldFlags & MYSQLI_PRI_KEY_FLAG) {
  echo 'this field is a primary key';
}

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