Optimize Delete - sql

Question

I have a importer system which updates the column of already existing rows in a Table. Since UPDATE was taking time I changed it to DELETE and BULK INSERT.
Here is my database setup snippet
Table: ParameterDefinition
Columns: Id, Name, Other Cols
Table: ParameterValue
Columns: Id, CustId, ParameterDefId, Value
I get the values associated to ParamterDefinition.Name from my XML source, so to import I first delete all the existing ParamterValue with all the ParamterDefinition.Name passed in the XML and finally do bulk insert of all the values from XML. Here is my query
DELETE FROM ParameterValue WHERE CustId = ? AND ParameterDefId IN (?,?...?);
For 1000 Customers the above DELETE statement is called 1000 times which is very time consuming now, approximately 64 seconds.
Is there any better way to handle DELETE of 1000 customers?
Thanks,
Sheeju

Answer 1

Create a temporary table for the bulk-insert (ParameterValue_Import). Do the bulk-inserts to this table, then update/insert/delete based on the imported data.
INSERT INTO .. SELECT .. WHERE NOT EXISTS ( .. ) for the new rows
UPDATE .. FROM for the updates
DELETE FROM WHERE NOT EXISTS ( .. ) for the deletion
Bulk operations have better performance than standalone operations. Most DBMSs are designed to handle set based operations instead of record based ones.
Edit
To delete or update one record based on a WHERE clause which refers to only one record, the DBMS should either do a full table scan (if there is no index for the where condition) or do an index lookup. Only after the record successfully identified, the DBMS proceeds the original request (update or delete). Based on the number of records in the table and/or the size/depth of the index, this could be really expensive. This process are done for each and every command in the batch. Summing up the total cost, it could be more than if you are updating/deleting records based on another table. (Especially if the operations are update/delete nearly all records in the target table.)
When you are trying to delete/update several records at once (e.g. based on another table), the DBMS could do the lookups with only one table scan/index lookup and do a logical join when processing your request.
The cost of purely updating a record is the same in each case, just the total cost of lookup could be significantly different.
Furthermore deleting then inserting a record to update it could require more resources: when you are deleting a record, all related indexes will be updates, and when you insert the new record, the indexes will be updated once more, while with updating the record, only those indexes should be updated, which are related to an updated column (and the index update should be done only once).

Answer 2

I am giving the exact syntax to the above idea given by #Pred
After Bulk Insert lets say you have data in "ParamterValue_Import"
To INSERT The Records in "ParamterValue_Import" which are not in "ParamterValue"
INSERT INTO ParameterValue (
CustId, ParameterDefId, Value
)
SELECT
CustId, ParameterDefId, Value
FROM
ParameterValue_Import
WHERE
NOT EXISTS (
SELECT null
FROM ParameterValue
WHERE ParameterValue.CustId = ParameterValue_Import.CustId
);
To UPDATE The Records in "ParamterValue" which are also in "ParamterValue_Import"
UPDATE
ParameterValue
SET
Value = ParameterValue_Import.Value
FROM
ParameterValue_Import
WHERE
ParameterValue.ParameterDefId = ParameterValue_Import.ParameterDefId
AND ParameterValue.CustId = ParameterValue_Import.CustId;