Multiple counts within a single SQL query

Question

I\'m trying to get the count of documents within 4 specific sections using the following code:

SELECT
    category.id
    , category.title
    , count(ts1.se         


        

Answer 1

@VoteyDisciple's answer is on the right track, but his query needs some improvements:

SELECT c.id, c.title,
    SUM(ts1.section_id = 1) AS doc1,
    SUM(ts1.section_id = 2) AS doc2,
    SUM(ts1.section_id = 3) AS doc3,
    SUM(ts1.section_id = 4) AS doc4
FROM category AS c
  LEFT JOIN category_link_section AS ts1
    ON (c.id = ts1.category_id)
GROUP BY c.id;

---

Explanations:

• The IF() expressions are redundant because equality already returns 1 or 0.
• Take the ts1.section_id=1 out of the join condition, or you'll never get the other section_id values.
• Group by c.id only. I assume the OP only wants one row per category, and columns for counts of each section_id value for the respective category. If the query grouped by c.id, ts1.section_id, then there'd be up to four rows per category.
• Move the commas in the select-list. Commas floating at the start of the line look ugly. ;-)

Answer 2

You might want to try something like this:

SELECT
    category.id
    , category.title
    , SUM(IF(ts1.section_id = 1, 1, 0)) AS doc1
    , SUM(IF(ts1.section_id = 2, 1, 0)) AS doc2
    , SUM(IF(ts1.section_id = 3, 1, 0)) AS doc3
    , SUM(IF(ts1.section_id = 4, 1, 0)) AS doc4
FROM
    category 
    LEFT JOIN category_link_section AS ts1
        ON (category.id = ts1.category_id AND ts1.section_id = 1)
GROUP BY category.id, ts1.section_id