MySQL-在所有符合结果的列中选择多个值

Question

I am trying to construct a query that will allow me to "filter" on pairs of columns for particular criteria. I need to be able to construct multiple filters for the same given pair. The end result should only return instances that have data for the case where all filters are applied.

I constructed a trivial example demonstrating what I would like to be able to do.

Using the follow table definition:

DROP TABLE IF EXISTS foo;

CREATE TEMPORARY TABLE `foo` (
  `ID` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `Index` INT UNSIGNED NOT NULL,
  `Header` VARCHAR(50) NOT NULL,
  `Value` VARCHAR(255) NOT NULL,
  PRIMARY KEY (`ID`),
  UNIQUE INDEX `ID_UNIQUE` (`ID` ASC));

INSERT INTO `foo` (`Index`, `Header`, `Value`)
VALUES
    (0, 'Header_1', 'a'),
    (0, 'Header_2', 'b'),
    (1, 'Header_1', 'a'),
    (1, 'Header_2', 'c');

I would like a query that would return the following, given that you are looking for the case where 'Header_1' == 'a' and 'header_2' == 'b':

Index | Header   | Value
------------------------
0     | Header_1 | a
0     | Header_2 | b

My current attempt is as follows:

SELECT `Index`, `Header`, `Value` FROM `foo`
    WHERE (
            (`Header` = 'Header_1') AND (`Value` = 'a')
        OR (
            (`Header` = 'Header_2') AND (`Value` = 'b')
        )
    )
GROUP BY `Header`, `Value`
HAVING COUNT(DISTINCT `Index`) = 2
ORDER BY `Index`, `Header`;

That code returns the following:

Index | Header   | Value
------------------------
0     | Header_1 | a

I am missing one of my return rows. How can I restructure the query to return all of the matching rows?

Note that I declared the table as a temporary table. This is important, as I am working with temporary tables, and they have special restrictions to keep in mind (namely not being able to open it more than once in the same statement).

Answer 1

Your query returns only header_1 because the clause:

HAVING COUNT(DISTINCT `Index`) = 2

is only correct for Header_1.

Header_2 has count=1, therefore removed from the end result.

To get a clearer picture of what i say use:

SELECT `Index`, `Header`, `Value`, COUNT(DISTINCT `Index`) FROM `foo`
    WHERE (
            (`Header` = 'Header_1') AND (`Value` = 'a')
        OR (
            (`Header` = 'Header_2') AND (`Value` = 'b')
        )
    )
GROUP BY `Header`, `Value`
ORDER BY `Index`, `Header`;

and take a look at the last column.

Answer 2

I couldn't figure out how to do this with only the one temporary table. I'm not happy with this result, but at least it works.

DROP TABLE IF EXISTS `foo2`;

CREATE TEMPORARY TABLE `foo2` (
    SELECT `Index` FROM `foo`
        WHERE (
            (`Header` = 'Header_1') AND (`Value` = 'a')
        OR (
            (`Header` = 'Header_2') AND (`Value` = 'b')
        )
    )
    GROUP BY `Index`
    HAVING COUNT(DISTINCT `Header`) = 2
);

SELECT DISTINCT t1.`Index`, t1.`Header`, t1.`Value` FROM `foo` t1
INNER JOIN `foo2` t2 ON t2.`Index` = t1.`Index`
ORDER BY t1.`Index`, t1.`Header`;

Answer 3

How about...

SELECT `index` 
  FROM foo 
 WHERE (header,value) IN (('header_1','a')) 
    OR (header,value) IN (('header_2','b')) 
 GROUP 
    BY `index` 
HAVING COUNT(*) = 2;