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這篇文章主要介紹了如何解決mysql多個(gè)字段update時(shí)錯(cuò)誤使用and連接字段的問題,具有一定借鑒價(jià)值,感興趣的朋友可以參考下,希望大家閱讀完這篇文章之后大有收獲,下面讓小編帶著大家一起了解一下。
執(zhí)行語句一
update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;
結(jié)果為只將book_id字段值更新為0,其他字段都沒有更改
mysql> select id,book_id,unit_id,article_id from spoken;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 5 | 55 | 55555 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
mysql> update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select id,book_id,unit_id,article_id from spoken;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 0 | 55 | 55555 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
執(zhí)行語句二
update spoken set book_id = 2,unit_id = 14,article_id = 47409 where id = 284989;(正常語句)
三個(gè)字段值都變更為給定值,
mysql> select id,book_id,unit_id,article_id from spoken;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 0 | 55 | 55555 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
mysql> update spoken set book_id = 2,unit_id = 14,article_id = 47409 where id = 284989;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select id,book_id,unit_id,article_id from spoken;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 2 | 14 | 47409 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
執(zhí)行語句三
update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;
只將第一個(gè)字段變更為1
mysql> select id,book_id,unit_id,article_id from spoken;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 2 | 14 | 47409 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
mysql> update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select id,book_id,unit_id,article_id from spoken;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 1 | 14 | 47409 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
分析,
1、正常的update語法為語句二,更新多個(gè)字段的值,多個(gè)字段之間使用逗號(hào)“,”分隔。
2、但問題語句一和問題語句三更新多個(gè)字段的值使用and ,分隔多個(gè)字段;
且語句一將book_id變更為,語句三將book_id變更為1;
一、問題語句一
update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;
等價(jià)于
update spoken set book_id = (2 and unit_id = 14 and article_id = 47409) where id = 284989;
等價(jià)于
update spoken set book_id = (2 and (unit_id = 14) and (article_id = 47409)) where id = 284989;
相當(dāng)于將book_id的值更新為下面語句的值
select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;
該語句由三個(gè)表達(dá)式通過mysql的邏輯運(yùn)算符and連接
表達(dá)式一為: 2
表達(dá)式二為:unit_id = 14 (select unit_id = 14 from spoken where id = 284989;)
表達(dá)式三為:article_id = 47409 (select article_id = 47409 from spoken where id = 284989;)
由于當(dāng)時(shí)unit_id = 55,article_id=55555
表達(dá)一的值為2
表達(dá)式二值為0
表達(dá)式三的值為0
所以select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;
的值為2 and 0 and 0 即為。
即執(zhí)行語句的結(jié)果等價(jià)于update spoken set book_id = 0 where id = 284989;
Mysql的邏輯運(yùn)算
http://www.cnblogs.com/pzk7788/p/6891299.html
邏輯與 ( AND 或 && )
(1) 當(dāng)所有操作數(shù)均為非零值、并且不為 NULL 時(shí),所得值為 1
(2) 當(dāng)一個(gè)或多個(gè)操作數(shù)為 0 時(shí),所得值為 0
(3) 其余情況所得值為 NULL
mysql> SELECT 1 AND -1, 1 && 0, 0 AND NULL, 1 && NULL ;
+----------+--------+------------+-----------+
| 1 AND -1
| 1 && 0
| 0 AND NULL | 1 && NULL |
+----------+--------+------------+-----------+
| 1 | 0 | 0
| NULL |
+----------+--------+------------+-----------+
二、同理可得語句三
2 and unit_id = 14 and article_id = 47409
相當(dāng)于將book_id的值更新為下面語句的值
select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;
該語句由三個(gè)表達(dá)式通過mysql的邏輯運(yùn)算符and連接
表達(dá)式一為: 2
表達(dá)式二為:unit_id = 14 (select unit_id = 14 from spoken where id = 284989;)
表達(dá)式三為:article_id = 47409 (select article_id = 47409 from spoken where id = 284989;)
由于當(dāng)時(shí)unit_id = 14,article_id=47409
表達(dá)一的值為2
表達(dá)式二值為1
表達(dá)式三的值為1
所以select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;
的值為2 and 1 and 1 即為1。
即執(zhí)行語句的結(jié)果等價(jià)于update spoken set book_id = 1 where id = 284989;
額外的問題:
Mysql如果對(duì)mysql的數(shù)值型如int做匹配時(shí),unit_id字段和14做匹配時(shí)
如下三個(gè)語句都匹配到結(jié)果
select id,book_id,unit_id,article_id from spoken where unit_id=14;
select id,book_id,unit_id,article_id from spoken where unit_id='14';
select id,book_id,unit_id,article_id from spoken where unit_id='14aaa';
(字符串轉(zhuǎn)數(shù)值會(huì)截取第一個(gè)非數(shù)字前面的數(shù)字)
mysql> select id,book_id,unit_id,article_id from spoken where unit_id=14;
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 0 | 14 | 47409 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
mysql> select id,book_id,unit_id,article_id from spoken where unit_id='14';
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 0 | 14 | 47409 |
+--------+---------+---------+------------+
1 row in set (0.00 sec)
mysql> select id,book_id,unit_id,article_id from spoken where unit_id='14aaa';
+--------+---------+---------+------------+
| id | book_id | unit_id | article_id |
+--------+---------+---------+------------+
| 284989 | 0 | 14 | 47409 |
+--------+---------+---------+------------+
1 row in set, 1 warning (0.00 sec)
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