Question

我有这样的SQL查询：

SELECT
   CONCAT(t1.a, t2.a, t2.b, t3.a, t4.a, t4.b) AS val
FROM
   t1 
   LEFT JOIN t2 ON ...
   LEFT JOIN t3 ON ...
   LEFT JOIN t4 ON ...

val输出为：0,1,0,1,2,1或1,2,0,1,0,2，...（按随机顺序包括0,1,2）

我想要计算每个数字的总数，如：0 =＆gt; 2,1 =＆gt; 3，2 =＆gt; 1，没有PHP代码

Answer 1

您可以简单地将现有查询包装在子查询中，并创建一个计算事件的外部查询;

SELECT 
  LENGTH(val) - LENGTH(REPLACE(val, '0', '')) zeros,
  LENGTH(val) - LENGTH(REPLACE(val, '1', '')) ones,
  LENGTH(val) - LENGTH(REPLACE(val, '2', '')) twos
FROM (
  SELECT
    CONCAT(t1.a, t2.a, t2.b, t3.a, t4.a, t4.b) AS val
  FROM
    t1 
    LEFT JOIN t2 ON ...
    LEFT JOIN t3 ON ...
    LEFT JOIN t4 ON ...
);

Answer 2

您需要使用UNION ALL。

SELECT tbl.col1, COUNT(tbl.col1)
FROM (
  SELECT t1.a as col1
    FROM t1
  UNION ALL
  SELECT t2.a as col1
    FROM t2
  UNION ALL
  SELECT t3.a as col1
    FROM t3
   ...
) tbl
GROUP BY tbl.col1;

SQLFIDDLE DEMO

Mysql查询从多列计数

2 个答案: