php+mysql 语句中被查询的字段可以设置变量么
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2022-06-03 14:20:14
...
比如:
$condition = "a_size";
$single_size = 30;
$sql_count = "select count(*) as count from foot_info WHERE '$condition' = '$single_size' ";
我这样运行,貌似什么也查询不到
但很奇怪,如果我用字符串连接成sql语句就可以正常查询,如下
$sql_count = "select count(*) as count from foot_info WHERE".$condition." = '$single_size' ";
/////////////////////////////////////
我又输出了上面两个sql语句的输出,分别是
select count(*) as count from foot_info WHERE Foot_Size = '30'//可运行
select count(*) as count from foot_info WHERE 'Foot_Size' = '30'//不可运行
回复内容:
比如:
$condition = "a_size";
$single_size = 30;
$sql_count = "select count(*) as count from foot_info WHERE '$condition' = '$single_size' ";
我这样运行,貌似什么也查询不到
但很奇怪,如果我用字符串连接成sql语句就可以正常查询,如下
$sql_count = "select count(*) as count from foot_info WHERE".$condition." = '$single_size' ";
/////////////////////////////////////
我又输出了上面两个sql语句的输出,分别是
select count(*) as count from foot_info WHERE Foot_Size = '30'//可运行
select count(*) as count from foot_info WHERE 'Foot_Size' = '30'//不可运行
把$condition的引号去掉就好。。
mysql的查询字段不需要加引号或者select count(*) as count from foot_info WHERE `Foot_Size` = '30'//可运行
select * from foot_info WHERE 1=1;
select * from foot_info WHERE 1=0;
在postgresql中表名和字段名是单引号;在Mysql中表名和字段名必须``或不写
一句话概括就是Mysql的单引号和双引号会被Mysql当成字符串处理,`符号内是表名或者字段处理
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