AND条件在MySQL查询中不起作用

Question

Please i need your help with my script. Whenever i include

AND maintable.semester_name = '$semester_name'

in the MySQL Query, it returns 0 for both values of semester_name, when actually only one is supposed to have a value of 0 when echo $nums is processed. When i remove

AND maintable.semester_name = '$semester_name'

the query gives normal results as i expect.

Thanks.

$query = "SELECT *             
   FROM maintable 
   WHERE maintable.matric_no = '$matric_no'
   AND   maintable.session = '$session'
   AND   maintable.semester_name = '$semester_name'
   AND   maintable.level = '$level'";
$result = mysql_query($query);
$nums = mysql_numrows($result);
echo $nums ;                  

TABLE STRUCTURE

COURSES
  course_id int(100) 
  course_code varchar(100) 
  course_title varchar(100) 
  course_unit int(10) 

MAINTABLE
  maintable_id int(255) 
  matric_no int(10) 
  session varchar(10) 
  semester_name varchar(10) 
  course_code varchar(10) 
  level int(10) 
  score int(10) 
  grade varchar(4) 

RESULT_UPLOAD
  upload_id int(10) 
  session varchar(10) 
  semester_name  varchar(10) 
  course_code varchar(10) 
  level varchar(10) 

SEMESTER
  semester_id int(10) 
  semester_name varchar(10) 

STUDENT
  matric_no int(10) 
  first_name varchar(100) 
  last_name varchar(100) 
  other_name varchar(100) 
  level int(10) 

USERS
  users_id int(10) 
  title varchar(20) 
  first_name varchar(20) 
  last_name varchar(20) 
  username varchar(20) 
  password varchar(100) 
  register_date datetime 
  tmp_name varchar(100) 
  type varchar(20) 
  name varchar(20) 
  size int(10) 

YEAR
  level_id int(10) 
  level int(10) 

Answer 1

Your query is correct, but with bit of ambiguity. The following query is run as exactly you are doing, but with less words.

$query = "SELECT *             
   FROM maintable 
   WHERE matric_no = '$matric_no'
   AND   session = '$session'
   AND   semester_name = '$semester_name'
   AND   level = '$level'";

Now, about your problem , the only way this might be happening may be due to no record is matching the records in your database.

Try to get the query you are running with echo $query and run the query directly from phpmyadmin to see how many result set you will get.

Answer 2

The query is correct. I guess your conditions really don't match any rows in the table. Just check what values you have in the database and what your are passing into the conditions.

Answer 3

试试这个查询...它的工作原理

$query = "SELECT *FROM maintable WHERE maintable.matric_no = '".$matric_no."'AND maintable.session = '".$session."' AND maintable.semester_name = '".$semester_name."' AND maintable.level = '".$level."' ";