CAMSET_L - Teradata Database

CAMSET_L

Purpose  

Compresses the specified Latin character data into the following possible values using a proprietary Teradata algorithm:

partial byte values (for example, 4-bit digits or 5-bit alphabetic letters)

one byte values (for example, other Latin characters)

Syntax  

where:

Syntax element…	Specifies…
TD_SYSFNLIB	the name of the database where the function is located.
Latin_string	a Latin character string or string expression.

Note: This function takes no arguments when used as part of the COMPRESS USING or DECOMPRESS USING phrases. For more information about the COMPRESS/DECOMPRESS phrase, see SQL Data Types and Literals.

ANSI Compliance

This is a Teradata extension to the ANSI SQL:2011 standard.

Argument Type and Rules

Expressions passed to this function must have a data type of VARCHAR(n) CHARACTER SET LATIN, where the maximum supported size (n) is 64000. You can also pass arguments with data types that can be converted to VARCHAR(64000) CHARACTER SET LATIN using the implicit data type conversion rules that apply to UDFs. For example, CAMSET_L(CHAR) is allowed because it can be implicitly converted to CAMSET_L(VARCHAR).

Note: The UDF implicit type conversion rules are more restrictive than the implicit type conversion rules normally used by Teradata Database. If an argument cannot be converted to VARCHAR following the UDF implicit conversion rules, it must be explicitly cast.

For details, see “Compatible Types” in SQL External Routine Programming.

The input to this function must be Latin character data.

If you specify NULL as input, the function returns NULL.

Result Type

The result data type is VARBYTE(64000).

Usage Notes

Uncompressed character data in Teradata Database requires one byte per character when storing Latin character data. CAMSET_L takes Latin character input, compresses it into partial byte or one byte values, and returns the compressed result.

CAMSET_L provides best results for short or medium Latin strings that:

contain mainly digits and English alphabet letters.

do not frequently switch between:

lowercase and uppercase letters.

digits and letters.

For a detailed comparison between the Teradata-supplied compression functions and guidelines for choosing a compression function, see Database Administration.

Although you can call the function directly, CAMSET_L is normally used with algorithmic compression (ALC) to compress table columns. If CAMSET_L is used with ALC, nulls are also compressed if those columns are nullable.

For more information about ALC, see “COMPRESS and DECOMPRESS Phrases” in SQL Data Types and Literals.

Uncompressing Data Compressed with CAMSET_L

To uncompress Latin character data that was compressed using CAMSET_L, use the DECAMSET_L function. See “DECAMSET_L” on page 530.

Example

In this example, the Latin values in the Description column are compressed using the CAMSET_L function with ALC. The DECAMSET_L function uncompresses the previously compressed values.

   CREATE MULTISET TABLE Pendants

      (ItemNo INTEGER,

       Gem CHAR(10) UPPERCASE CHARACTER SET LATIN,

       Description VARCHAR(1000) CHARACTER SET LATIN

          COMPRESS USING TD_SYSFNLIB.CAMSET_L

          DECOMPRESS USING TD_SYSFNLIB.DECAMSET_L);

Example

Given the following table definition:

   CREATE TABLE Pendants

      (ItemNo INTEGER,

       Description VARCHAR(100) CHARACTER SET LATIN);

 

The following query returns the compressed values of the Description column.

   SELECT TD_SYSFNLIB.CAMSET_L(Pendants.Description);