How Can master..spt_values Be Used for Efficient Column Splitting in SQL Server?

Why and How to Utilize master..spt_values for Column Splitting

Purpose of master..spt_values

Despite its undocumented status, master..spt_values is a valuable table that enables system procedures in Microsoft SQL Server to perform various functions effectively. It contains a collection of reference tables and projection data used by these system procedures, including lookup values for data types, roles, and other metadata.

Understanding Type = 'P'

Type = 'P' signifies the Projection table within master..spt_values. This table provides a consecutive sequence of numbers, from 0 to 2047, that can be used to perform projections or traversals through data.

Leveraging spt_values for Column Splitting

The raw data stored in master..spt_values is not intended for direct use by user queries. However, its projection capabilities are particularly useful for splitting data within a single column.

Imagine a table where one column contains a comma-separated list of values, such as '1,2,3'. To transform this column into multiple rows, you can utilize spt_values as follows:

SELECT
    RIGHT(LEFT(T.col4,Number-1),
    CHARINDEX(',',REVERSE(LEFT(','+T.col4,Number-1))))
FROM
    master..spt_values,
    table1 T
WHERE
    Type = 'P' AND Number BETWEEN 1 AND LEN(T.col4)+1 AND
    (SUBSTRING(T.col4,Number,1) = ','
    -- OR SUBSTRING(T.col4,Number,1)  = '') --this does not work correctly anyway

In this scenario, the query iterates through the spt_values table (Type = 'P') and uses the number sequence to guide the split operation. It effectively isolates each value within the comma-separated list, creating distinct rows in the result set.

Benefits of Using spt_values for Column Splitting

Employing master..spt_values for column splitting offers several advantages:

• Efficiency: By utilizing the existing table and sequence of numbers, the query avoids the overhead of creating and populating temporary tables.
• Flexibility: The projection table provides a wide range of numbers, allowing for various splitting operations on columns with differing lengths.
• Compatibility: master..spt_values is a built-in system table and thus universally available in SQL Server installations, ensuring compatibility and reliability.

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