sql - mysql - 按多列频率排序

Question

我有一个包含 5 列的表格:

• 标记 1
• 标签 2
• 标签 3
• 标记 4
• 标签 5

如果我想显示按这些标签的流行度(频率)排序的结果，我会使用哪种查询？

Answer 1

因为表格没有规范化，所以你必须先把它展平:

SELECT a.column, a.tag1 AS tag
  FROM TABLE a
UNION ALL
SELECT b.column, b.tag2
  FROM TABLE b
UNION ALL
SELECT c.column, c.tag3
  FROM TABLE c      
UNION ALL
SELECT d.column, d.tag4
  FROM TABLE d
UNION ALL
SELECT e.column, e.tag5
  FROM TABLE e

...在你数数之前:

SELECT t.tag, COUNT(*) tag_popularity
  FROM (SELECT a.column, a.tag1 AS tag
          FROM TABLE a
        UNION ALL
        SELECT b.column, b.tag2
          FROM TABLE b
        UNION ALL
        SELECT c.column, c.tag3
          FROM TABLE c      
        UNION ALL
        SELECT d.column, d.tag4
          FROM TABLE d
        UNION ALL
        SELECT e.column, e.tag5
          FROM TABLE e) x
GROUP BY x.tag
ORDER BY tag_popularity DESC