what is the difference between update and merge in oracle?
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Both the MERGE and UPDATE statements are designed to modify data in one table based on data from another, but MERGE can do much more. Whereas UPDATE can only modify column values you can use the MERGE statement to synchronize all data changes such as removal and addition of row.
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ALTER is used to update the structure of the table (add/remove field/index etc). Whereas UPDATE is used to update data. The ALTER changes the table in the database, you can add or remove columns, etc. ... ALTER is used to change things like table structures or stored procs, otherwise known as DDL statements.
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Merge joins are faster and uses less memory than hash joins. Hash join is used when projections of the joined tables are not already sorted on the join columns. In this case, the optimizer builds an in-memory hash table on the inner table's join column.
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append adds observations to the existing variables. That is an oversimplification because append does not require that the datasets have the same variables. ... merge adds variables to the existing observations. That is an oversimplification because merge does not require that the datasets have the same observations.
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Modifying Field Values with Update Queries An Update Query is an action query (SQL statement) that changes a set of records according to criteria (search conditions) you specify. ... Update Queries let you modify the values of a field or fields in a table.
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In upsert operation Salesforce internally validates the data based on Object's Id or External Id. So, upsert takes little bit longer time than insert or update . Using the upsert operation, you can either insert or update an existing record in one call.
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A Merge Join is designed to produce results similar to how JOINs work in SQL. The Lookup component does not work like a SQL JOIN. ... With a Merge Join you will get the desired output. With a Lookup, where input 2 is the look up source, the output will be one row per invoice, no matter how many rows exist in input 2.
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Merging is used to collect data for the same key variable (e.g., customer ID) from different sources. Concatenation is used to assemble different portions of the same data fields for different segments of the key variable.
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While the SET statement reads observations from one data set at the time, the MERGE statement reads from two or more data sets simultaneously. The PDV contains all variables from all data sets: you are combining the observations from the data sets in the MERGE statement into one observation.
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IKM Oracle Incremental Update. Integrates data into an Oracle target table in incremental update. Erroneous data can be isolated into an error table and can be recycled in next execution of interface. When using this module with a journalized source table, it is possible to synchronize deletions.
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mlocate is a merging locate and database package. "Merging" means updatedb reuses the existing database to avoid re-reading most of the file system. ... mlocate can index several file systems including network file systems for network shares.
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In SQL the putting together the records from different input files is called a join. A match-merge also puts together records from different input files. However, the match-merge and the join use two entirely different techniques of matching the records from the input files. ... As its name implies SQL is a query language.
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SOQL has no equivalent INSERT, UPDATE, and DELETE statements. In the Salesforce world, data manipulation is handled using a set of methods known as DML (Data Manipulation Language). ... In SOQL, you specify each field name to return. Beyond that, the SELECT statement that SOQL provides is similar to SQL.
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Functionally, save and insert are very similar, especially if no _id value is passed. However, if an _id key is passed, save() will update the document, while insert() will throw a duplicate key error.
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An upgrade is the act of replacing your product with a newer, and often more superior, version or similar product. Therefore, an update modifies your current product while an upgrade totally replaces it. ... On the other hand, upgrades are distinct and do not need the older software to function.
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A JDBC batch update is a batch of updates grouped together, and sent to the database in one batch, rather than sending the updates one by one. Sending a batch of updates to the database in one go, is faster than sending them one by one, waiting for each one to finish.
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4 Answers. Views in Oracle may be updateable under specific conditions. ... An updatable view is one you can use to insert, update, or delete base table rows. You can create a view to be inherently updatable, or you can create an INSTEAD OF trigger on any view to make it updatable.