sql - Mysql Help - Left join -

-

i read other threads , first question here. here goes;

i'm trying build query involves 2 tables, course table , studentslink table. studentslink table describes link between students , course. tables below;

course     courseid(bigint) - pk coursename (varchar) courseinstructor (varchar)  studentslink courseid(bigint) - pk studentid(bigint) - pk  below sample data;  course table  id | coursename| courseinstructor ---------------------------------- 1  | algebra 1 | mike 2  | english 2 | james 3  | english 3 | john 4  | algebra 2 | mike 5  | history 1 | tony  studentlink table  studentid | courseid   ---------------------- 100       | 2          101       | 3          102       | 3         102       | 4          103       | 4          100       | 1          103       | 3          103       | 2

the desired outcome below given if looking student number 103

id | coursename| courseinstructor |studentid | courseid  --------------------------------------------------------- 1  | algebra 1 | mike             | null     | null 2  | english 2 | james            | 103      | 2 3  | english 3 | john             | 103      | 3 4  | algebra 2 | mike             | 103      | 4 5  | history 1 | tony             | null     | null

the query have far below;

select *  course left join studentlink  on course.courseid = studentlink.courseid studentlink.studentid = 103 or (studentlink .studentid null , studentlink.courseid null) order studentlink.courseid desc

i'm trying result set of out courses available, 1 particular student registered in , 1 not able display course can offer student.

i have tried many variations of query , did research. i'm not asking teh codez little bit of guidance wonderful. i've been stuck @ few days while trying work other parts of project @ same time.

any appreciated. in advance.

select id, coursename, courseinstructor, studentid, courseid  courses c  left join studentlink sl on c.id = sl.courseid  , studentid = 103

Comments

Post a Comment

Popular posts from this blog

php - What is the difference between $_SERVER['PATH_INFO'] and $_SERVER['ORIG_PATH_INFO']? -

-
what’s difference between $_server['path_info'] , $_server['orig_path_info'] ? how use them? when run print_r($_server) , path_info , orig_path_info not present in array. why not? how can enable them? i have read php manual on them, still don’t understand them. the path_info variable present if invoke php script this: http://www.example.com/phpinfo.php/hello_there it's /hello_there part after .php script. if don't invoke url that, there won't $_server["path_info"] environment variable. the porig_ prefix uncommon. path_info standard cgi-environment variable, , should never prefixed. did read that? (there issues around php3/php4 if invoked php interpreter via cgi-bin/ - hardly has such setups today.) for reference: http://www.ietf.org/rfc/rfc3875
Read more

fortran - Function return type mismatch -

-
i'm attempting recode old c++ program in fortran make use of lapack (i'm aware c++ have lapack++, i'm having lot of trouble installing it, gave up). i didn't have problems compilation, when had variables declared real . when started coding section of program required lapack, found parameters passed dsyev need double precision . tried change double precision (including changing hard coded numbers double precision counterparts, i.e. 0.0 -> 0.0d0) when try compile, following error of functions , subroutines i've written: error: return type mismatch of function <function> @ (1) (real(4)/real(8)) i'm not sure coming from, in program has been changed double precision. for example, i've declared following: double precision :: alpha(3),d(3),zeta1,zeta2 double precision :: a1(3),a2(3),d1(3),d2(3) double precision :: pi pi = 3.14159265359d0 alpha = (/0.109818d0, 0.405771d0, 2.22766d0/) d = (/0.444635d0, 0.535328d0, 0.154329d0 /) 10 i=1,3 ...
Read more

queue - mq_receive: message too long -

-
i implementing communication between 2 processes using queue. problem when call function mq_receive, error: message long. i have done following: struct mq_attr attr; long size = attr.mq_msgsize; .... // initializing queue "/gateway" int rc = mq_receive(gateway, buffer, size, &prio); if print size value, size=1, while when print same size program (got same mechanism), not long integer ( -1217186280 )... how can solve error?....so while size = 1, believe it's right "message long" why 1? p.s. have tried put : int rc = mq_receive(gateway, buffer, sizeof(buffer), &prio); but no result. it seems need read docs more carefully. when call mq_receive should pass size of destination buffer. this size must greater mq_msgsize attribute of queue . in addition, seems have error in queue attributes initialisation makes proper mq_receive call impossible. here standard message queue session: fill mq_attr struct ( doc ): struct mq_a...
Read more