如何把如果LIMIT MySQL的其他條件

Question

這裏是我的查詢

$where_or = " 
       AND 
        content_status = 'Active' 
       AND 
        content_post_status = 'published' 
       AND 
        deleted = 0 
       AND 
        content_type = '$type' 
       ORDER BY content_created_at DESC "; 

     $select = "content_id, content_title, content_short_description, content_url, content_created_at"; 

     $query = $this->db->query(" 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 54 
        $where_or 
        LIMIT 3 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 55 
        $where_or 
        LIMIT 2 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 56 
        $where_or 
        LIMIT 2 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 57 
        $where_or 
        LIMIT 1 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 58 
        $where_or 
        LIMIT 1 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 60 
        $where_or 
        LIMIT 1 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 61 
        $where_or 
        LIMIT 1 
       ) 
       UNION ALL 
       (
        SELECT $select 
        FROM tbl_content 
        WHERE 
        content_category_id = 118 
        $where_or 
        if content_type = 'article' 
        begin 
         LIMIT 10 
        end 
       ) 
     "); 

可以在最後UNION看到我想提出的限制。如果條件..但它給我的錯誤...我怎麼能這樣做...請幫助..

Answer 1

你不能這樣做與MySQL，至少不是你想要的方式。如果你仔細想想這個：

if content_type = 'article' 
begin 
    LIMIT 10 
end 

沒有意義。 LIMIT應用於一個集合而不是單個記錄。如果你寫的是有效的SQL，並且你的數據包含content_type ='article'的真實內容和一些錯誤的內容。你期望會發生什麼？

Answer 2

我建議你排名記錄，然後添加WHERE條件篩選記錄content_category_id及其排名。在這種情況下，您將避免使用多個SELECT ... FROM查詢。