Updating millions of rows bulk collect
Because the TOP clause is only applied after these clauses are applied, each execution either inserts one genuinely unmatched row or updates one existing row.
The following example creates a source and target table and then presents the correct method of using the TOP clause to modify the target in batch operations.
That is, there is no order in which the rows are distributed among the actions defined in the WHEN clauses.
For example, specifying TOP (10) affects 10 rows; of these rows, 7 may be updated and 3 inserted, or 1 may be deleted, 5 updated, and 4 inserted and so on.
The objective is to have a table with both longitude/latitude values and the extra columns type and desc too.
TABLE1 ( POSTCODE VARCHAR2(8 BYTE) PRIMARY KEY, EASTING VARCHAR2(7 BYTE), NORTHING VARCHAR2(7 BYTE), FULLCOUNTY VARCHAR2(32 BYTE), LONGITUDE NUMBER(14,10), LATITUDE NUMBER(14,10), TYPE INTEGER, TYPE_DESC VARCHAR2(100 BYTE) ) TABLE2 ( POSTCODE VARCHAR2(8 BYTE) EASTING VARCHAR2(7 BYTE), NORTHING VARCHAR2(7 BYTE), FULLCOUNTY VARCHAR2(32 BYTE), LONGITUDE NUMBER(14,10), LATITUDE NUMBER(14,10), ) I was excited thinking it is a very simple job and kicked off an update statement as below UPDATE table1 t1 SET (longitude, latitude) = (SELECT longitude, latitude FROM table2 t2 WHERE t1.postcode = t2.postcode) But this statement took atleast 7 minutes and I could not see any sign of completion.
Product Inventory AS pi USING (SELECT Product ID, SUM(Order Qty) FROM Sales. To improve query performance, we recommend the following parameterization guidelines: In the MERGE statement, the TOP clause specifies the number or percentage of rows that are affected after the source table and the target table are joined, and after rows that do not qualify for an insert, update, or delete action are removed.
Fact Buying Habits AS Target USING (SELECT Customer ID, Product ID, Purchase Date FROM dbo. For more information about query hints, see USE Adventure Works2008R2; GO BEGIN TRAN; MERGE Production. Therefore, MERGE statements that contain literal values may not perform as well as individual INSERT, UPDATE, or DELETE statements because a new plan is compiled each time the MERGE statement is executed.Today I came across a problem There were 2 large tables each containing about 2.2 millions rows with the structure as shown below.The longitude and latitude are not populated on table table1 where as it was populated in table2. I was requested to populate table1 with longitude and latitude values from table2 based on postcode which was the primary key on both the tables.By using the MERGE statement, you can replace the individual DML statements with a single statement.This can improve query performance because the operations are performed within a single statement, therefore, minimizing the number of times the data in the source and target tables are processed. Purchase Date) OUTPUT $action, Inserted.*, Deleted.*; The join operation in the MERGE statement is optimized in the same way as a join in a SELECT statement.When checked the session it was actively reading data and longops suggested that it would take more than a day to complete.Wondering why I realised that postcode was not indexed on table 2.By doing so, the entire file is processed in a single batch.To improve the performance of the bulk merge process, we recommend the following guidelines: These guidelines ensure that the join keys are unique and the sort order of the data in the source file matches the target table.However, performance gains depend on having correct indexes, joins, and other considerations in place. Purchase Date WHEN NOT MATCHED BY TARGET THEN INSERT (Customer ID, Product ID, Last Purchase Date) VALUES (Source. That is, when SQL Server processes joins, the query optimizer chooses the most efficient method (out of several possibilities) of processing the join. When the source and target are of similar size and the index guidelines described previously in the 'Index Best Practices' section are applied to the source and target tables, a merge join operator is the most efficient query plan.This topic provides best practice recommendations to help you achieve optimal performance when using the MERGE statement. This is because both tables are scanned once and there is no need to sort the data. Order Qty If a SELECT, INSERT, UPDATE, or DELETE statement is executed without parameters, the SQL Server query optimizer may choose to parameterize the statement internally.