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plurals

POMultiple JOINS - Mysql
primarykey
Id
20019172
data
AcceptedAnswerId
20019558
AnswerCount
2
ClosedDate
CommentCount
1
CommunityOwnedDate
CreationDate
2013-11-16T13:45:17.450
FavoriteCount
0
LastActivityDate
2013-11-16T15:17:10.793
LastEditDate
2013-11-16T14:24:48.553
LastEditorUserId
2590247
OwnerUserId
2590247
ParentId
0
PostTypeId
1
Score
2
ViewCount
48
LastEditorDisplayName
text
Body
I have 4 tables: Classes: <pre><code>id class 1 X C 2 VI B 3 XII F 4 X C 5 VI B 6 VIII A </code></pre> Students: <pre><code> id id_student class 2 1 [->] X C 3 4 [->] VI B 5 7 [->] X C </code></pre> Grades <pre><code>Id id_student grade 3 1 [->] 8 4 1 [->] 7 5 1 [->] 10 6 1 [->] 8 7 1 [->] 9 8 4 [->] 5 9 4 [->] 7 10 4 [->] 9 11 1 [->] 4 12 1 [->] 9 13 7 [->] 10 </code></pre> Absences: <pre><code>id id_student 1 1 [->] 2 1 [->] 3 1 [->] 4 4 [->] 5 1 [->] 6 1 [->] 7 1 [->] 8 7 [->] </code></pre> What I want is to select all classes from Classes Table (only those who have students) and count the number of students for every class, the average of their grades and number of absences. This is what I have: <pre><code>SELECT classes.class, COUNT(distinct students.id_students) AS nr_students, AVG(grades.grade) AS avg_grades FROM classes INNER JOIN students ON students.student = clases.class INNER JOIN grades ON students.students = grades.id_student GROUP BY class </code></pre> Until now everything is great. Output (PHP): <pre><code>Class Nr_Students Avg_Grades VI B 1 7.0000 X C 2 8.1250 </code></pre> But I want to count every row from Absences table and print the total number of absences for every class. This is what I'm trying to do: <pre><code>Class Nr_Students Avg_Grades Nr_Abcences VI B 1 7.0000 1 X C 2 8.1250 7 </code></pre> I can't change the DB! Thank you.
Tags
<mysql>
Title
Multiple JOINS - Mysql
singulars
PostAcceptedAnswerId
1. PO
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 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. USComy
UserOwnerUserId
1. USComy
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
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 PostTypePostTypeId
 PTAnswer
2. PO
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 PTAnswer
VotesPostIdCreationDate
1. VO
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 PostPostId
 POMultiple JOINS - Mysql
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
2. VO
 singulars
 PostPostId
 POMultiple JOINS - Mysql
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 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
CommentsPostId
1. COyour `JOIN ON` conditions look highly suspect
 singulars
 PostPostId
 POMultiple JOINS - Mysql
 UserUserId
 USOGHaza

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Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.