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Thread: SAMPLE BLOCK in select

  1. #1
    Join Date
    Nov 2000
    Posts
    15

    SAMPLE BLOCK in select

    What is the implication of the SAMPLE BLOCK(1) in the following query?

    SELECT COUNT(*) from TABLE_A SAMPLE BLOCK(1)

    I assumed that this would return all of the rows in the first block of the TABLE_A data segment, but the number of rows that is being returned is over 100,000 and with a 16K block size I can hardly believe that there are that many rows in one block.
    Michael Auer
    Oracle DBA/Developer
    Oracle8i OCP

  2. #2
    Join Date
    Jun 2000
    Location
    Madrid, Spain
    Posts
    7,447
    if I rememebr right it tells how more or less how many rows are there, it estimates number of rows per block then multiply by the total number of blocks

  3. #3
    Join Date
    Jun 2000
    Location
    Madrid, Spain
    Posts
    7,447
    ops

    this is the definition

    sample_clause
    The sample_clause lets you instruct Oracle to select from a random sample of rows from the table, rather than from the entire table.

    BLOCK
    BLOCK instructs Oracle to perform random block sampling instead of random row sampling.

    See Also: Oracle8i Concepts for a discussion of the difference


    sample_percent
    sample_percent is a number specifying the percentage of the total row or block count to be included in the sample. The value must be in the range .000001 to (but not including) 100.

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