![]() If you want to make sure your query checks your role in different tables, another slight modification can be done. So the ELSE block will be entered in case of no duplication, and we can avoid the RACE CONDITION as such. Rather than entering this code block all the time to check, we can make sure that our queries only use this code block if there is a RACE CONDITION at all else, skip it and walk through. ![]() Hence, we can now make a simple adjustment. The solution above tends to be expensive due to the EXCEPTION clause added inside a code block.ĭue to difficulty entering and exiting this code block containing the EXCEPTION clause, this tends to happen. To prevent the RACE condition, we can use the solution given above and append it to the query we have used here. Another transaction would have already come here and raised the notice, which may invalidate this operation. RACE conditions tend to be an issue in this solution because if you call the IF EXISTS check and wait for the query to raise the notice if it returns TRUE. So make sure to know where you define your roles, then modify the code as it works suitably with your conditions. However, this may return an error if your role is not defined under the PG_ROLES table. IF EXISTS (SELECT FROM pg_catalog.pg_roles However, other times, you might have roles defined in PG_ROLES under the catalog, and you may be required to change your code to the following. This may be a modification of the solution provided above.ĬREATE ROLE MARK LOGIN PASSWORD 'mark123' īecause we created the role inside the PG_USER table, we call the IF EXISTS in the SELECT statement from this table. We can create a procedure with the IF EXISTS condition to RAISE NOTICE if a duplicate violation is found. Use IF EXISTS to Define Duplication Violation Condition Unlike the solutions provided below, this works perfectly considering other circumstances. It works perfectly as this does not have a delay between checking and calling the duplicate exception.Īlso, if you call this from a different language or PL/SQL script, it will still issue the correct return SQLSTATE. This solution helps prevent RACE conditions. SQLERRM is short for SQL ERROR MESSAGE and contains a string that describes the error message with the returning SQLSTATE.ĭO initiates a code block, mostly a procedure, inside a transaction. Other errors or faults will be skipped, and NOTICE won’t be raised. Meaning that it will only throw an error if duplication is found. In our statement, we raised a NOTICE when an EXCEPTION is caught on a duplicate_object. Syntax of the CASE statement: CASE WHEN condition THEN result Then you can use the CASE clause to specify a result you want to achieve once the desired condition is met. You will notice the use of the EXCEPTION clause, which can be found under ERRORS and MESSAGES in the PostgreSQL documentation. To understand how the query works, look at its structure. Output: NOTICE: role "mark" already exists, moving to the next statement If a duplicate role is found, the above query will issue a simple statement (shown below), then move on to the next query. We can use this to our advantage and issue an EXCEPTION on duplication to avoid the error, rather than the whole script going defunct.ĮXCEPTION WHEN duplicate_object THEN RAISE NOTICE '%, moving to next statement', SQLERRM USING ERRCODE = SQLSTATE PL/PgSQL is used to have FOR loops and control structures rather than a simple SQL statement. To solve this, we can use a few of the methods defined below: Use CREATE ROLE With an EXCEPTION in PL/PgSQL Output: ERROR: role "mark" already exists If the user already exists, you will get the error below. Instead of LOGIN, you can even go for WITH to define a password for this user. This allows our role, MARK, to have a password. If the user does not already exist, running the above will return SUCCESSFUL. Let us go ahead and create a user MARK with a password to log in to our database.Ĭode: create role MARK LOGIN PASSWORD 'mark123' Other options in the syntax have been omitted and can be viewed here. PostgreSQL provides us with a method to define new roles. Use the CREATE ROLE Method to Create Role if It Does Not Exist in PostgreSQL Depending on the system required, there may be a need to have multiple users or roles in a PostgreSQL database. Today, we will be learning how to create a role in PostgreSQL if it does not exist.Ī role is an entity that owns objects in the database defined by us and can be made to have different privileges. Use the CREATE ROLE Method to Create Role if It Does Not Exist in PostgreSQL.
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