MySQL中 and or 查詢的優先級分析

這個可能是容易被忽略的問題,首選我們要清楚:
MySQL中,AND的執行優先級高於OR。也就是說,在沒有小括號()的限制下,總是優先執行AND語句,再執行OR語句。
比如:

select * from table where  條件1 AND 條件2 OR 條件3
等價於
select * from table where  ( 條件1 AND 條件2 )  OR 條件3

select * from table where  條件1 AND  條件2 OR 條件3 AND 條件4
等價於
select * from table where (  條件1 AND  條件2  ) OR (  條件3 AND 條件4  )

來點事例深入理解下:

測試表數據:

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for book
-- ----------------------------
DROP TABLE IF EXISTS `book`;
CREATE TABLE `book` (
 `id` int(10) UNSIGNED NOT NULL AUTO_INCREMENT,
 `name` varchar(25) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,
 `author` varchar(25) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,
 `price` decimal(10, 2) DEFAULT NULL,
 PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of book
-- ----------------------------
INSERT INTO `book` VALUES (1, 'PHP', 'mate', 21.00);
INSERT INTO `book` VALUES (2, 'JAVA', 'kaven', 23.00);
INSERT INTO `book` VALUES (3, 'JAVA高級', 'loose', 45.00);
INSERT INTO `book` VALUES (4, 'GO', 'jim', 46.00);
INSERT INTO `book` VALUES (5, 'GO設計', 'json', 76.00);
INSERT INTO `book` VALUES (6, 'PHP高級編程', 'bate', 67.00);
INSERT INTO `book` VALUES (7, 'Python', 'jim', 66.00);
INSERT INTO `book` VALUES (8, 'Python設計', 'mali', 54.00);
INSERT INTO `book` VALUES (9, 'GO編程', 'kaven', 86.00);
INSERT INTO `book` VALUES (11, 'Python3', 'jim', 55.00);

SET FOREIGN_KEY_CHECKS = 1;

查詢方式1:

SELECT * FROM book WHERE author='jim' OR author='json' AND name='PHP';

上面的查詢等價於:

SELECT * FROM book WHERE author='jim' OR (author='json' AND name='PHP');

那麼上面的查詢結果就很好理解瞭。

查詢方式2:

SELECT * FROM book WHERE name='PHP' AND author='jim' OR author='json';

上面的查詢等價於:

SELECT * FROM book WHERE (name='PHP' AND author='jim') OR author='json';

查詢方式3:

SELECT * FROM book WHERE name='GO' AND (author='jim' OR author='json');

這個就很好理解瞭。瞭解and or的優先級。這些查詢也就不是呢麼”理解混淆”瞭。

到此這篇關於MySQL中 and or 查詢的優先級分析的文章就介紹到這瞭,更多相關MySQL and or 查詢內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet!

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