Find Uneven Distribution | Teradata Vantage - Finding Uneven Distribution Using Hash Functions - Teradata Vantage - Analytics Database

Use the following functions to identify uneven hash distribution of data.

HASHAMP Example

If you suspect distribution problems (skewing) among AMPS, the following is a sample of what you might enter for a three-column PI:

SELECT HASHAMP (HASHBUCKET (HASHROW (col_x, col_y, 
      col_z))), count (*)
FROM hash15 
GROUP BY 1
ORDER BY 2 desc;

HASHROW Example

If you suspect collisions in a row hash, the following is a sample of what you might enter for a three-column PI:

SELECT HASHROW (col_x, col_y, col_z), count (*)
FROM hash15 
GROUP BY 1
ORDER BY 2 desc
HAVING count(*) > 10;