MySQL使用BETWEEN子句返回错误的结果

Question

我正在使用以下查询从mysql数据库中获取数据，但获取了错误的数据。我想显示1990〜2000年的release_year，但它显示了所有内容。

SELECT title,release_year
FROM FILMS
WHERE 
    release_year BETWEEN 1990 AND 2000
    AND budget > 1000000000
    AND language ='Spanish'
    OR language = 'French';

我试图切换查询的顺序，但是它似乎不起作用，或者我尝试在release_year between 1990 AND 2000上加上括号。

Answer 1

尝试一下。

SELECT title,release_year 
FROM FILMS WHERE release_year >= 1990 
AND release_year <= 2000 
AND budget > 1000000000 
AND (language ='Spanish' OR language = 'French');

如有任何疑问，请在下面评论。

Answer 2

您有一个逻辑上的先决条件问题。

这些是您的过滤条件：

release_year BETWEEN 1990 AND 2000 
AND budget > 1000000000 
AND language ='Spanish'
OR language = 'French'

在逻辑运算符中，OR的优先级比AND的低，因此在语法上等效于：

( 
    release_year BETWEEN 1990 AND 2000 
    AND budget > 1000000000 
    AND language ='Spanish'
)
OR language = 'French'

现在您可以看到，无论发行年份和预算如何，此表达式都将允许任何法国电影。

您可能想要：

release_year BETWEEN 1990 AND 2000 
AND budget > 1000000000 
AND ( language ='Spanish' OR language = 'French')

可以缩写为：

release_year BETWEEN 1990 AND 2000 
AND budget > 1000000000 
AND language IN ('Spanish', 'French')

Answer 3

强制逻辑and和or优先总是一个好主意。

尝试：

SELECT title,release_year 
FROM FILMS 
WHERE release_year between 1990 AND 2000 
AND budget > 1000000000 
AND (language ='Spanish' OR language = 'French')
;

或

SELECT title,release_year 
FROM FILMS 
WHERE release_year between 1990 AND 2000 
AND budget > 1000000000 
AND language IN ('Spanish', 'French')
;

MySQL的最新版本对IN进行了优化，使其性能优于等效的OR条件集。

注意，我说“总是” 是因为，即使(a and b) or c是您想要的逻辑，加上括号也会使您的意图对查看查询的下一个人清楚。