Oracle: OCA-047-question and Experiment

Oracle: OCA-047-solution and experiment, the MERGE statement is a new syntax for Oracle9i to merge update and INSERT statements. Use the MERGE statement to query a table or subquery

Oracle: OCA-047-solution and experiment, the MERGE statement is a new syntax for Oracle9i to merge update and INSERT statements. Use the MERGE statement to query a table or subquery

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Question:

Answer:

This topic describes the usage of merge. The concepts are as follows:

The MERGE statement is a new syntax of Oracle9i, used to merge update and INSERT statements. Use the MERGE statement to query another table based on the connection conditions of one table or subquery, and UPDATE the matching connection conditions. The INSERT statement cannot be executed. This syntax only requires one full table scan to complete all the work, and the execution efficiency is higher than INSERT + UPDATE.

In the question, when matched then: first update the row value, and THEN delete the NULL row. Therefore, the third row is deleted. Not matched then: the rows that do NOT meet the conditions are inserted directly, so you can determine the answer.