42 lines
938 B
SQL
42 lines
938 B
SQL
-- example 1
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-- ========== 0 =========
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start transaction;
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-- A先查询
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select *
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from customer;
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-- ========== 1 =========
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-- ========== 2 =========
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-- 在 B 添加数据后，A 尝试进行修改。奇怪的是，明明查询不到，居然可以修改成功
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update customer
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set username = 'wuhu'
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where id = 1;
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-- A 再次查询表中数据，发现修改的那一行现身了
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select *
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from customer;
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commit;
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-- ========== 3 =========
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-- example 2
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-- ========== 0 =========
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start transaction;
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-- A先查询，查到数据如下：
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-- 1,Fortern
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-- 2,Maxin
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-- 3,MooGeo
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select *
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from customer;
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-- ========== 1 =========
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-- ========== 2 =========
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-- A 备份表中数据到另一个表
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insert into customer_back select * from customer;
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commit;
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-- 结果备份表中的数据居然是被其他事物修改的数据！！
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select * from customer_back;
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-- 为什么会这样？
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-- ========== 3 =========
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select * from customer where id = 1; |