MySQL：每行计数列数

Question

我只想知道计数列是否可行，因为您在不调用每个列名的情况下计算行数。例如：

SELECT COUNT(FOUND COLUMNS) AS counted FROM table WHERE a_value EXISTS IN COLUMNS

/* 

The same as this specified one. This is working but I'm 
looking for another approach without calling each column name.

SELECT (IF(col1="Y",1,0) + IF(col2="Y",1,0)) as counted FROM table

*/

我希望每行都会抛出结果，如：

|  counted  |
|-----------|
|     2     |
|     1     |
|     0     |

是否可能？如果是，怎么样？

Answer 1

TABLE_SIZE

试试这个它会起作用。

Answer 2

我认为你正在寻找那个

THE SCHEMA

CREATE TABLE `numbers`( `col1` INT, `col2` INT, `col3` INT, `col4` INT ); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('0', '0', '0', '6'); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('1', '0', '0', '9'); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('4', '1', '0', '2'); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('9', '5', '1', '3'); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('5', '0', '6', '4'); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('2', '0', '1', '6'); 
INSERT INTO `numbers` (`col1`, `col2`, `col3`, `col4`) VALUES ('8', '5', '6', '7'); 

计算每行的值'0'

SELECT (c1+c2+c3+c4) AS counted FROM 
(
SELECT 
CASE WHEN col1 = 0 THEN 1 ELSE 0 END AS c1,
CASE WHEN col2 = 0 THEN 1 ELSE 0 END AS c2,
CASE WHEN col3 = 0 THEN 1 ELSE 0 END AS c3,
CASE WHEN col4 = 0 THEN 1 ELSE 0 END AS c4
FROM numbers
) AS temp_count

  

/ 结果 /

     

计数

    3
    2
    1
    0
    1
    1
    0

计算每行的“7”值

SELECT (c1+c2+c3+c4) AS counted FROM 
(
SELECT 
CASE WHEN col1 = 7 THEN 1 ELSE 0 END AS c1,
CASE WHEN col2 = 7 THEN 1 ELSE 0 END AS c2,
CASE WHEN col3 = 7 THEN 1 ELSE 0 END AS c3,
CASE WHEN col4 = 7 THEN 1 ELSE 0 END AS c4
FROM numbers
) AS temp_count

因此，如果要检查其他值，则必须替换col1 = 7，col2 = 7，col3 = 7，col4 = 7的值。