Again thanks . Now it is more clear for me after checking information about unique index. Again I am not a DB guy , but more on embedded systems where I also have to deal with concurrency and race conditions on another level .
OK let's take the hypothetical situation again .
Let's say I created the unique index on Name after the table is created.
Thread A and B have the same snapshot of the table at the beginning where there is no bob in any row . Thread A writes bob in a row successfully , and then when Thread B tries to write the name bob , an error notification will appear indicating name bob is already in the row . Is this right ??
Thanks