Oracle - AND之間的區別（Case1或Case2或Case3）

Question

大家好我有一個相當簡單的問題。

我想知道什麼

SELECT * 
    FROM TABLE 
WHERE A = 'xxx' 
    AND (B = 'xxx' OR C='xxx' OR D='xxx') 

而這個查詢

SELECT * 
    FROM TABLE 
WHERE A = 'xxx' 
    AND B = 'xxx' 
    OR C='xxx' 
    OR D='xxx' 

之間的差別在底部的查詢將返回2個結果與上面的查詢返回結果爲零。

Answer 1

這

SELECT * FROM TABLE 
WHERE A = 'xxx' AND (B = 'xxx' OR C='xxx' OR D='xxx') 

相當於該

SELECT * FROM TABLE 
WHERE A = 'xxx' AND B = 'xxx' OR 
     A = 'xxx' AND C = 'xxx' OR 
     A = 'xxx' AND D = 'xxx' 

你把在WHERE子句遵循布爾表達式規則的邏輯。就像代數表達式一樣，有一個命令操作。一般情況下，順序是

1. 不
2. 和
3. 或

Answer 2

A = 'xxx' AND B = 'xxx' OR C='xxx' OR D='xxx' 

相當於

(A = 'xxx' AND B = 'xxx') OR (C='xxx') OR (D='xxx') 

感謝operators precedence order