Sql 统计表列中重复值的出现次数

我有一个表，其中每列都包含整数，有些值是重复的。 下面是一个例子：

| ColumnA    | Column B    | Column C |
|       2    |        3    |        1 |     
|       1    |        1    |        3 |   
|       2    |        1    |        3 |  

如何执行SQL查询以统计每个整数的出现次数？ 我想得到这样的东西： 2的计数是2，1的计数是4，3的计数是3

SELECT Col, COUNT(*) AS TOT
FROM (
    SELECT ColumnA AS Col FROM table
    UNION ALL
    SELECT ColumnB FROM table
    UNION ALL
    SELECT ColumnC FROM table
) AS A
GROUP BY Col

试试这个：

SELECT Col, COUNT(*) AS TOT
FROM (
    SELECT ColumnA AS Col FROM table
    UNION ALL
    SELECT ColumnB FROM table
    UNION ALL
    SELECT ColumnC FROM table
) AS A
GROUP BY Col