CODEWITHSUNDEEP
oracle-database
michael nesterenko
michael nesterenko

Reputation: 14439

concurrent table update

Does following update query always leave table data unchanged?

update mytable set column1 = column1

Wonder if there will be lost updates?

Initially column1 has value oldValue. There are two transactions (t1 and t2) and t2 starts in the middle of t1.

t1: update mytable set column1 = 'newValue'

and

t2: update mytable set column1 = column1

as t2 transaction started later than t1 it also finished later than t1.

The question: what value will be assigned to the column1?

Upvotes: 0

Views: 220

Answers (1)

Amir Pashazadeh
Amir Pashazadeh

Reputation: 7282

Transaction isolation level is what to isolate different transactions, and if you use read committed or higher isolation levels, there won't be any problem.

By the way as far as I know your first query never updates any record in Oracle, even with "read uncommitted" isolation level.

Upvotes: 1

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