Queries to it locks the row, provides the next value, and then unlocks the row, thereby guaranteeing uniqueness. Oracle sequences (and I have done the same in DB2) keep an underlying table with the sequence name and next value. The performance of identifying the maximum value depends on the number of records in the table. DB2 SEQUENCE NUMBER CODE* not shown here: code to check if the sequence exists and createĬonnection to Oracle (select &sequence.nextval from dual) The heart of the macro has code like: proc sql noprint Once the sequences are established another macro gets the next sequence val. I recently created a sas macro that uses Oracle passthru to initialise such Oracle sequences from the current maximum value (+ 1) The database guarantees that no numbers are duplicated - which can happen if concurrently executing SAS programs all get the max value from a table and deduce the next number. This is is especially useful is the numbers being sequenced are id columns and the tables may get records added by multiple program which may potentially run in parallel. The data type can be any exact numeric data type (SMALLINT, INTEGER, BIGINT, or DECIMAL with a scale. If you have access to a database like Oracle, then I recommend the use of database sequences to ensure you keep sequences clean. Specifies the data type to be used for the sequence value. DB2 SEQUENCE NUMBER HOW TOThe solution i have come up with doesn't seem very elegant, and I'm worried it will be prone to errors once implemented at a larger scale.Īny thoughts on the likelihood of errors that could occur, or how to improve the solution?Ĭreate table int1 as select *, max(seq_have) as seq_max from example group by id The order of the observations without sequence numbers is arbitrary, as long as it doesn't overlap and is larger then the largest number of the existing sequence inside the group. Then there's a possibility another thread got the same NEXT VALUE and tries to insert the same value, resulting in a DB2 -803 error.I have data where i have a broken sequence of numbers (seq_have) where i want to continue the sequence from largest number in the existing sequence for each ID, for the observations with missing sequence numbers. The ranking function returns a ranking value for each row. The Rank function can be used to generate a sequential number for each row or to give a rank based on specific criteria. It uses SQL functions RowNumber, Rank, and Denserank. Store the value in a variable and pass that in to the INSERT: This article explains how you can generate sequence numbers in SQL select query. Then there's a possibility another INSERT was run between the above INSERT and SELECT, hence providing me the incorrect value. I know you can use "NEXT VALUE FOR colname" in both INSERT and SELECT statements, but I can't figure out how to both INSERT and SELECT with the same value without risking a race condition in a multithreaded application. We are now being pressured to switch to Sequence instead. SELECT IDENTITY_VAL_LOCAL() FROM SYSIBM.SYSDUMMY1 A sequence value is generated for a NEXT VALUE expression each time a row is retrieved. To do that we would run the below 2 queries in the same transaction: In the past we've mostly used Identity columns for tables where we needed an auto-generated unique identifier. I am working on a multithreaded application that uses DB2 for its primary database.
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