In the event that all the transactions are read-only, the entire second phase is avoided.
在所有事务均为只读的情况下，可以避免整个第二阶段。
SQL transactions fall into two basic types, read and write.
SQL事务可分为两种类型：读和写。
Read committed -- The transaction can read data committed by other transactions.
Readcommitted（读已提交） ——事务可以读取由另一事务提交的数据。
Read committed -- The transaction can read data committed by other transactions.
Readcommitted（读已提交） ——事务可以读取由另一事务提交的数据。
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