NonStop SQL/MP Reference Manual

Table Of Contents
NonStop SQL/MP Reference Manual142115
D-18
Considerations—DCOMPRESS
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Unsigned exact numeric: NUMERIC (1 to 9) or PIC 9V9 COMP (not
NUMERIC (10) or larger or PIC S9)
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Unsigned decimal: includes PIC 9V9 DISPLAY
For compression method 2, the new method, the following data types are supported:
°
Fixed-length character: CHARACTER or PIC X
°
Unsigned integer: INTEGER or SMALLINT (not LARGEINT)
°
Unsigned exact numeric: NUMERIC (1 to 9) or PIC 9V9 COMP (not
NUMERIC (10) or larger or PIC S9)
°
Unsigned decimal: DECIMAL UNSIGNED, includes PIC 9V9 DISPLAY
°
Date and time data types: DATE, DATETIME, TIMESTAMP, and TIME
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Multibyte character types: NATIONAL CHARACTER, NCHAR
DCOMPRESS 2 does not support the following data types:
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CHAR VARYING
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VARCHAR
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NUMERIC SIGNED
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SMALLINT | INTEGER signed
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LARGEINT signed
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FLOAT | REAL | DOUBLE PRECISION
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DECIMAL signed
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INTERVAL
You cannot use DCOMPRESS on a file with a clustering key. You cannot use the
COLLATE option on a key column if you will be using DCOMPRESS.
How keys are compressed
The file system compresses keys by eliminating leading characters duplicated from
one key to the next and replacing them with a one-byte count of the duplicate
characters:
Key compression can actually require an additional byte per record. It saves the
most space when many key values have similar beginnings.
Series of Uncompressed
Keys Same Keys, Compressed
JONES, JANE 0JONES, JANE
JONES, JOHN 8OHN
JONES, SAM 7SAM