Question

我有这个简单的MYSQL table1：

和这个表2：

 id | question | answer
  1 |  how     | 
  2 |  are     | fine
  3 |  you     | ok

这个简单的查询：

SELECT table1.id,COUNT(answer NOT NULL) FROM table1 LEFT JOIN table2
       ON table1.id = table2.id

我想计算非空答案字段。我尝试了NOT NULL，但由于answer列为NOT NULL而无效，因此它不适用，因为它会导致主查询不返回任何内容

Answer 1

您可以使用CHAR_LENGTH(str)函数来检查值的长度。使用以下查询：

SELECT COUNT(answer) FROM table WHERE CHAR_LENGTH(answer)>0;

来自Reference Doc.

编辑：
您可以尝试此查询：

SELECT COUNT(answer) FROM table1 LEFT JOIN table2
       ON table1.id = table2.id AND CHAR_LENGTH(table2.answer)>0

Answer 2

你可以试试这个，捕捉空白的一切：

SELECT COUNT(id) FROM table
where answer IS NOT NULL or answer <>''

这应该抓住并计算“回答”中具有任何值的任何行。

或者，如果有联接：

SELECT     table1.count(id), table2.question
FROM         table1 LEFT OUTER JOIN
                      tabel1 ON table1.id = table2.id
GROUP BY table1.id,table2.question
HAVING      (table2.answer <> '') OR (table2.answer IS NOT NULL)

Answer 3

只计算具有NULL答案的行数！

SELECT COUNT(1) FROM table /* COUNT(1) will go on counting rows frequncy*/
where answer IS NOT NULL

Answer 4

如果答案列不可为空，则IS NOT NULL将返回所有行。你想要的是“不是空字符串”：

SELECT COUNT(*)
FROM table
WHERE answer <> "";

如果答案可以为空，那么您可以检查两种情况：

SELECT COUNT(*)
FROM table
WHERE answer IS NOT NULL AND answer <> "";

Answer 5

   SELECT COUNT(t2.answer) count
     FROM table1 t1 
LEFT JOIN table2 t2
       ON t2.id = t1.id
      AND t2.answer != ''

OR

   SELECT t1.id, COUNT(t2.answer) count
     FROM table1 t1 
LEFT JOIN table2 t2
       ON t2.id = t1.id
      AND t2.answer != ''
 GROUP BY t1.id

Answer 6

您可以使用此SUM(CHAR_LENGTH((answer))/CHAR_LENGTH((answer)))公式计算非空答案字段。

SELECT table1.id, SUM(CHAR_LENGTH((answer))/CHAR_LENGTH((answer))) FROM table1

LEFT JOIN table2 ON table1.id = table2.id

Answer 7

计算每个列：

SELECT count(`id`) + count(`personal_id`) + count(`f_name`) + ... 
FROM `detail_members` WHERE `personal_id` = '$personalid'

计算MYSQL中的非空字段

7 个答案: