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Trying to Generate Dynamic Sequence IDs as Stored Function or Stored Procedure
Posted by: James Dekker
Date: January 04, 2011 11:45PM

Am using MySQL 5 on OS X - Snow Leopard...

Have working code in place which obtains the highest sequence number ID from a sequence table and then increments and assigns it to its corresponding table:

The original code's purpose is to dynamically increments a specific table's last sequence id and set its corresponding table's id to that new value.



1. Original Code Snippet (which is working):

-- Get last sequence number

replace into my_sequence_id_s set id =
(select max(CONVERT(sequence_id, signed)) from my_table_t);

-- Increments the number

insert into my_sequence_id_s set id = null;

-- Saves the number as a variable

set @dynamicId = last_insert_id();

-- Print

select @dynamicId;


2. Refactoring:

DROP PROCEDURE IF EXISTS generate_dynamic_id#

CREATE PROCEDURE generate_dynamic_id

(IN _sequence_table varchar(40),
IN _actual_table varchar(40),
IN _id_field VARCHAR(40),
OUT dynamic_id varchar(40))

-- Get Last Sequence Number
set @getLastSequenceNumberSQL =
concat('REPLACE INTO ', _sequence_table, 'SET ID =
(select max(CONVERT(',_id_field,', signed))
from ', _actual_table, ');');
prepare lastRecordStmt from @getLastSequenceNumberSQL;
execute lastRecordStmt;
deallocate prepare lastRecordStmt;

-- Increments the number.
set @createNewSequenceNumberSQL =
concat('insert into ', _sequence_table ,' set id = null;');
prepare newSequenceNumberStmt from @createNewSequenceNumberSQL;
execute newSequenceNumberStmt;
deallocate prepare newSequenceNumberStmt;

-- Set the number as a dynamic variable.
set @dynamic_id = last_insert_id();


3. Here's the calling function (which fails):**

-- Get dynamically incremented id

call generate_dynamic_id(
'my_sequence_id_s', 'my_table_t', 'table_id', @dynamicId);



You have an error in your SQL syntax;

check the manual that corresponds to your MySQL server version

for the right syntax to use near

'ID = (select max(CONVERT(id_field, signed)) from my_table_t)' at line 1


For some odd reason, dynamic function calls are not allowed in Stored Functions or Triggers, so that's why a Stored Procedure was used.

As you can see, I am setting up varchars at the parameters and then trying to concatenate them as strings and run them inside prepared statements.

Is there a better way to generate incremented sequence IDs and then assign them to dynamic variables?

Can this be done in a stored function?

Any help would be greatly appreciated...

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Trying to Generate Dynamic Sequence IDs as Stored Function or Stored Procedure
January 04, 2011 11:45PM

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