Question

I want to store only last 200 data (if 201 data is coming means i need to delete 1 row and so on….)to table in database.Is there any logic?

Thanks

Answer 1

I don’t think you can do this in a single statement. Suppose a table has a primary key column ‘id’, a data column ‘dataCol’, and a time stamp column ‘dataTime’. Here’s an approach (untested) that deletes the oldest row whenever the number of rows exceeds 200:

INSERT INTO t (dataCol, dataTime) VALUE ('data', NOW);
DELETE FROM t
 WHERE 200 < (SELECT COUNT (*) FROM t)
   AND id = (SELECT id FROM t ORDER BY dataTime LIMIT 1);

If you aren’t going to delete data for any reason other than that the table is full, then another approach is possible. (No idea if this is better.) Start by pre-populating the table with 200 entries. Then create a second table with bookkeeping information about what’s in the first table. The second table would have a single row that keeps the following information:

• the next slot to be filled
• whether the first table is full

The idea is that you insert new data into the first table at the index specified by the second table, increment the second table’s slot column modulo 200, and set the full column to 1 the first time the slot pointer wraps back to 0.