php - 在一个查询中访问 3 个表

Question

我想将数据从一个表复制到另一个表。怎么办？

$P_studentnumber=mysql_real_escape_string($_POST['studentnumber']);
$P_subjectcode=mysql_real_escape_string($_POST['subjectcode']);
$P_semester=mysql_real_escape_string($_POST['semester']);

$sql "INSERT units INTO grades (units) FROM subjects WHERE subjectcode='$P_subjectcode'"; //<--THIS IS THE PART THAT I WOULD WANT TO ADD

$sql="INSERT INTO grades (studentnumber,course, subjectcode, semester, instructorname, units) SELECT '$P_studentnumber', course, '$P_subjectcode', '$P_semester','$instructorname', 'units' FROM students WHERE studentnumber='$P_studentnumber'";

Answer 1

你可以试试:

INSERT table1(col1,col2) SELECT col1,col2 FROM table2