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POCreating a new column using CASE and maybe count
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  1. POCreating a new column using CASE and maybe count
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    copied!<p>Right now, I have a query that gets me 3 columns.</p> <blockquote> <p><strong>SELECT</strong> a.studentID, a.classdetailID, c.course_title<br> <strong>FROM</strong> studentcoursedetails a, classdetails b, course c<br> <strong>WHERE</strong> b.classdetailID = a.classdetailID<br> <strong>AND</strong> b.courseID = c.courseID<br> <strong>ORDER BY</strong> c.course_title, b.classdetailID</p> </blockquote> <p>What I get is a column that shows the ID of the student that did the course, the ID of the class they were in and the title of the course itself. Something along these lines:</p> <pre><code>5---8----Airline Security Operations 4---8----Airline Security Operations 6---8----Airline Security Operations 4---9----Airline Security Operations 8---10---Airline Security Operations 5---10---Airline Security Operations 1---1----Airport Design and Construction 4---1----Airport Design and Construction 2---1----Airport Design and Construction 1---2----Airport Design and Construction </code></pre> <p>What I need is a table that shows me something like this:</p> <pre><code>course_title Number of Classes Number of students Airline Security Operations 3 4 </code></pre> <p>I thought of using <code>CASE</code>, but when I think about it, I just get lost. I'd appreciate your help.</p> <p>The answer, thanks to gbn:</p> <blockquote> <p><strong>SELECT</strong> c.course_title, COUNT( DISTINCT a.studentID ) AS "Students in Course" , COUNT( <strong>DISTINCT</strong> a.classdetailID ) AS "Total Classes"<br> <strong>FROM</strong> studentcoursedetails a<br> <strong>JOIN</strong> classdetails b ON b.classdetailID = a.classdetailID<br> <strong>JOIN</strong> course c ON b.courseID = c.courseID<br> <strong>GROUP</strong> BY c.course_title</p> </blockquote>
 

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