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4 Ιουλ 2012 · Please try this: SELECT * FROM EMP_MASTER T1 LEFT JOIN TRANSFER T2 ON T1.employee_id=T2.employee_id WHERE NVL(T2.DATE_OF_TRANSFER,SYSDATE) =NVL((SELECT MAX(T3.DATE_OF_TRANSFER) FROM TRANSFER T3 WHERE T3.employee_id=T2.employee_id),SYSDATE);
The optimizer can use the following operations to join two row sources: Nested Loops Join. Sort-Merge Join. Cluster Join. Hash Join. Nested Loops Join . To perform a nested loops join, Oracle follows these steps: The optimizer chooses one of the tables as the outer table, or the driving table. The other table is called the inner table.
Nested loops joins are useful when the database joins small subsets of data, the database joins large sets of data with the optimizer mode set to FIRST_ROWS, or the join condition is an efficient method of accessing the inner table.
SELECT l.sku_id AS ProductId, l.is_primary AS IsPrimary, v1.category_name AS Category1, v2.category_name AS Category2, v3.category_name AS Category3, v4.category_name AS Category4, v5.category_name AS Category5 FROM category c4 JOIN category_voc v4 ON v4.category_id = c4.category_id and v4.language_code = 'en' JOIN category c3 ON c3.category_id ...
Oracle always uses nested loops for left lateral joins. What makes lateral joins useful is that predicates derived from columns in the driving row source (i.e. the row source specified before the LATERAL keyword) can be used in the probe row source (i.e. the inline view that follows LATERAL).
27 Απρ 2022 · Join Methods are the techniques used by the Oracle Optimizer to join data coming from two data producing operators in an execution plan. You can find the individual Join Methods chosen by the Optimizer in the Operations column of an Execution table.
Nested Loops. The process for nested loops is: Read rows from the first (outer) data set; For each row in this, query the second (inner) data set for matching rows; Repeat until all the rows are read from the outer table or the client stops fetching rows; This query to find all rows with different values in each table uses nested loops:
