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4.20 The Object Class »
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4.19.2.21. NdbTransaction::scanIndex()

Description.  This method is used to perform an index scan of a table, using NdbRecord. The scan may optionally be ordered.

Signature.  

NdbIndexScanOperation* scanIndex
    (
      const NdbRecord* key_record,
      const char* low_key,
      Uint32 low_key_count,
      bool low_inclusive,
      const char* high_key,
      Uint32 high_key_count,
      bool high_inclusive,
      const NdbRecord* result_record,
      NdbOperation::LockMode lock_mode = NdbOperation::LM_Read,
      const unsigned char* result_mask = 0,
      Uint32 scan_flags = 0,
      Uint32 parallel = 0,
      Uint32 batch = 0
    )

Note

For multi-range scans, the low_key and high_key pointers must be unique. In other words, it is not permissible to reuse the same row buffer for several different range bounds within a single scan. However, it is permissible to use the same row pointer as low_key and high_key in order to specify an equals bound; it is also permissible to reuse the rows after the scanIndex() method returns — thatis, they need not remain valid until execute() time (unlike the NdbRecord pointers).

Parameters.  This method takes the following parameters:

  • The key_record describes the index to be scanned. It must be a key record on the index; that is, the columns which it specifies must include all of the key columns of the index. It must be created from the index to be scanned, and not from the underlying table.

  • low_key determines the lower bound for a range scan.

  • low_key_count determines the number of columns used for the lower bound when specifying a partial prefix for the scan.

  • low_inclusive determines whether the lower bound is considered as a >= or > relation.

  • high_key determines the upper bound for a range scan.

  • high_key_count determines the number of columns used for the higher bound when specifying a partial prefix for the scan.

  • high_inclusive determines whether the lower bound is considered as a <= or < relation.

  • The result_record describes the rows to be returned from the scan. For an ordered index scan, result_record be a key record on the index; that is, the columns which it specifies must include all of the key columns of the index. This is because the index key is needed for merge sorting of the scans returned from each fragment.

  • The lock_mode for the scan must be one of the values specified in Section 4.15.1.3, “The NdbOperation::LockMode Type”.

  • The result_mask pointer is optional. If it is present, only columns for which the corresponding bit (by attribute ID order) in result_mask is set will be retrieved in the scan. The result_mask is copied internally, so in contrast to result_record need not be valid when execute() is invoked.

  • scan_flags can be used to impose ordering and sorting conditions for scans. See Section 4.18.1, “The NdbScanOperation::ScanFlag Type”, for a list of permitted values.

  • The parallel argument is the desired parallelism, or 0 for maximum parallelism (receiving rows from all fragments in parallel), which is the default.

  • batch determines whether batching is employed. The default is 0 (off).

Return Value.  The current NdbIndexScanOperation, which can be used for error checking.