Updates that affect primary or secondary index values, on the other hand, are implemented as discrete delete and insert operations. The following table explains the differences in truncation behavior. Processing time can also vary between different syntaxes used to perform the identical update operation.
Update values are set in the corresponding row column values according to the rules for host variables. The best practice is to avoid using the UPDATE statement on a queue table because the operation requires a full table scan to rebuild the internal queue table cache.
You should reserve this statement for exception handling. The following rules apply to updating the partitioning columns of a PPI table:. The system aborts the request. It does not update the base table or the sparse join index, and returns an error. The system stores the row in the appropriate partition, which might be different from the partition in which it was stored, and continues processing requests.
When you design your partitioning expressions, you should construct them in such a way that expression errors either cannot, or are very unlikely to, occur.
The specified value is not constrained by identity column parameters. To update a distinct type column, either of the following must be true:. To update a structured type column, the updated value must be of the same structured type.
For example, suppose you have the following table definition:. Valid invocation of the constructor function with the NEW syntax. The result is an address value whose attribute values are set to their defaults. The result is an updated address value with its street attribute modified.
The result is another updated address value with its zip attribute modified. This result also contains the change to the street attribute. Mutator SET clauses provide a syntax for updating structured type columns.
Each mutator method name you specify must be a valid mutator method name for the respective structured type value. As implemented by Teradata, any column references in an expression refer to the value of the column in the row before the row is updated. The system converts the two example clauses to the following single equality expression:. According to the ANSI SQL standard, the column reference to mycol in the second example equality expression of the mutator SET clause should reflect the change made to it from the first equality expression of the mutator SET clause, the assignment of x.
In other words, the two equality expressions are converted to the following single equality expression:. To update rows using a view through which the table is accessed, observe the following rules:. The following table explains the differences in truncation behavior. However, you can specify a Period column that is not defined as part of a partitioning expression for both equality and inequality conditions on that column for an upsert request.
If both BEGIN and END bounds are specified in the partitioning expression of the table, then only an equality condition on both bounds is treated as a bound matching condition.
This must result in a single partition. You also cannot modify the values of those partitioning columns; otherwise, the system aborts the request and returns an error message to the requestor.
Updating a base table row does not always cause inserts or updates to a join index on that base table. The system aborts the request. It does not update the base table or the sparse join index, and returns an error. The system stores the row in the appropriate partition, which might be different from the partition in which it was stored, and continues processing requests.
Expression evaluation errors, such as divide by zero, can occur during the evaluation of a partitioning expression. The system response to such an error varies depending on the session mode in effect at the time the error occurs. Design your partitioning expressions so that expression errors cannot, or are very unlikely to, occur. If you specify a Period column as part of the partitioning expression for a target PPI table, you can only specify equality conditions on that column for an upsert request on that table.
An upsert request cannot specify inequality conditions on a Period column that is specified in a partitioning expression for the table. However, an upsert request can specify a Period column that is not defined as part of a partitioning expression for equality and inequality conditions on that column.
If you specify a Period column in an upsert request, it must be a term in an equality condition. If the partitioning expression for a target PPI table specifies a Period bound function, then an equality condition on the bound function is treated as a PPI bound matching condition.
If BEGIN and END bounds are specified in the partitioning expression of the table, only an equality on both bounds is processed as a bound matching condition. The best practice is to avoid using the UPDATE statement on a queue table because the operation requires a full table scan to rebuild the internal queue table cache.
You should reserve this statement for exception handling. A simple upsert is a standalone update operation for which a subsequent standalone insert operation is coded that is performed only if the specific row to be updated is found not to exist. Learn more. Asked 9 years, 7 months ago. Active 7 years, 8 months ago.
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