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Table 9-3 Operation options
Operator Description
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| Operator | Description |
|---|---|
| Step | This operator indicates the start of the specified step Subtree. |
| Table |
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| Scan | This operator indicates that a table scan was performed on the specified table to receive the required data. The More column displayed in the ToolTip and in the Statistics tab specify the scan direction (forward/backward), the I/O size and the buffer replacement strategy. When there is no useful index, the optimizer performs a table scan to receive the required data. |
| Index |
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| Scan | This operator indicates that an index scan was performed on the specified index to receive the required data. The More column displayed in the ToolTip and in the Statistics tab specify the scan direction (forward/backward), the I/O size and the buffer replacement strategy. |
| Index |
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| Seek | This operator indicates that an index seek was performed on the specified index to receive the required data. The More column displayed in the ToolTip and in the Statistics tab specify the scan direction (forward/backward), the I/O size and the buffer replacement strategy. |
| Clustered Index |
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| Scan | This operator indicates that a clustered index scan was performed on the specified index to receive the required data. The More column displayed in the ToolTip and in the Statistics tab specify the scan direction (forward or backward), the I/O size and the buffer replacement strategy. |
| Clustered Index |
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| Seek | This operator indicates that a clustered index seek was performed on the specified index to receive the required data. The More column displayed in the ToolTip and in the Statistics tab specify the scan direction (forward or backward), the I/O size and the buffer. |
| Table |
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| Lookup | This operator indicates that in addition to an access to the index pages, there is an access to the data pages of the table to receive the required data which is not included in the index itself. The More column displayed in the ToolTip and in the Statistics tab specify the I/O size and the buffer replacement strategy. |
| Nested |
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| Loops | This operator indicates that the join between the two result sets under this operator is of type Nested Loops. The first operator under the Nested Loops operator is the outer table in the join and the second operator under the Nested Loops operator is the inner table in the join. |
| Merge |
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| Join | This operator indicates that the join between the two result sets under this operator is of type Merge Join. |
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| Sort | This operator indicates that a sort operation was performed on the rows returned from the previously executed operation (appears just below this operator) in a specific order, optionally eliminating duplicate entries. |
| Aggregate |
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| This operator indicates that an Aggregate operation was performed on the rows returned from the previously executed operation (appears just below this operator). This operator appears in steps, which perform an evaluation of grouped or ungrouped aggregate functions such as SUM, AVERAGE and COUNT. |
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| Subquery | This operator indicates that a subquery was executed. The Subquery tree will appear under this operator. The More column displayed in the ToolTip and in the Statistics tab specify the nesting level of the subquery, the predicate type (IN, ANY, EXISTS, or EXPRESSION), and the type of query (correlated/ non-correlated). |
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| Spooling | This operator indicates that a temporary worktable was created to hold intermediate results. Temporary worktables are created in cases when the statement cannot be executed in one step. For example, if the statement contains an Order By clause and the optimizer cannot use an index to order the resulting rows, it creates a worktable to sort the resulting rows before returning them. The More column displayed in the ToolTip and in the Statistics tab specify why the temporary worktable was created (Order By, Distinct, Reformatting, and so on). |
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| Join | This operator indicates that a join operation was performed between a subquery output and another result set. |
| Parallelism |
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| Merge | This operator indicates that a parallelism merge was done to the result sets returned by all the worker processes involved in the parallel execution. The More column displayed in the ToolTip and in the Statistics tab specify the way in which the results of parallel scans were merged. |
| Log |
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| Scan | This operator indicates that a log scan operation was performed. |
About the costs that are available in the plan tree
Precise for Sybase uses the DBCC TRACEON (310,311) command to receive the Estimated I/O needed to execute the statement. Since Sybase supplies Estimated I/O only to table-based operations, not all operators in the Plan tree contain I/O Costs. In cases of access both to the index pages and data pages, meaning a Table Lookup is being performed, Sybase provides the Total I/O operations needed while accessing the table. Therefore, the I/O Costs are displayed in the Table Lookup operator and it applies both to the index access and table access. The following operators contain the Total Estimated I/O Costs of their Subtree operators: The entire statement, STEP N and Subquery N.
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