MySQL中的INTERSECT

Question

我有两个表,记录和数据.记录有多个字段(名字,姓氏等).这些字段中的每一个都是存储实际值的数据表的外键.我需要搜索多个记录字段.

下面是使用INTERSECT的示例查询,但我需要一个在MySQL中工作的查询.

SELECT records.id FROM records, data WHERE data.id = records.firstname AND data.value = "john"
INTERSECT
SELECT records.id FROM records, data WHERE data.id = records.lastname AND data.value = "smith"

谢谢你的帮助.

Answer 1

您可以使用内部联接筛选在另一个表中具有匹配行的行:

SELECT DISTINCT records.id 
FROM records
INNER JOIN data d1 on d1.id = records.firstname AND data.value = "john"
INNER JOIN data d2 on d2.id = records.lastname AND data.value = "smith"

许多其他选择之一是一个in条款:

SELECT DISTINCT records.id 
FROM records
WHERE records.firstname IN (
    select id from data where value = 'john'
) AND records.lastname IN (
    select id from data where value = 'smith'
)

Answer 2

我认为这种方法更容易理解,但由于您最初加载了大量重复记录,因此会产生一些开销.我在具有大约10000-50000条记录的数据库上使用它,并且通常相交大约5个查询,并且性能是可接受的.

你要做的只是"UNION ALL"你要交叉的每个查询,看看你每次都得到了哪些.

SELECT * From (

    (Select data1.* From data1 Inner Join data2 on data1.id=data2.id where data2.something=true)
    Union All
    (Select data1.* From data1 Inner Join data3 on data1.id=data3.id where data3.something=false)

) As tbl GROUP BY tbl.ID HAVING COUNT(*)=2 

因此,如果我们在两个查询中都获得相同的记录,那么它的计数将为2,最终的环绕查询将包含它.

Answer 3

请改用联接:

SELECT records.id
FROM records
JOIN data AS D1 ON records.firstname = D1.id
JOIN data AS D2 ON records.lastname = D2.id
WHERE D1.value = 'john' and D2.value = 'smith'

这是一些测试数据:

CREATE TABLE records (id INT NOT NULL, firstname INT NOT NULL, lastname INT NOT NULL);
INSERT INTO records (id, firstname, lastname) VALUES
(1, 1, 1),
(2, 1, 2),
(3, 2, 1),
(4, 2, 2);

CREATE TABLE data (id INT NOT NULL, value NVARCHAR(100) NOT NULL);
INSERT INTO data (id, value) VALUES
(1, 'john'),
(2, 'smith');

预期结果:

2

测试数据可能对海报没有用,但对于想要检查解决方案以确定其工作正常的选民,或者想要提交答案以便他们可以测试自己答案的人来说,这可能是有用的.