Vertica Analytics Platform Version 9.2.x Documentation

FROM Clause

A comma-separated list of data sources to query.

Syntax

FROM dataset[,…] [ TABLESAMPLE(percent) ]

Parameters

dataset

A set of data to query, one of the following:

TABLESAMPLE(percent)

Valid only for user-defined tables, specifies to return a random sampling of records, where percent specifies the approximate sampling size. The percent value must be between 1 and 99, inclusive, and can include decimal values. The number of records returned is not guaranteed to be the exact percentage specified.

All rows of the data have equal opportunities to be selected. Vertica performs this sampling before applying all other query filters.

Examples

Count all records in customer_dimension table:

=> SELECT COUNT(*) FROM customer_dimension;
 COUNT
-------
 50000
(1 row)

Return a small sampling of rows in table customer_dimension:

=> SELECT customer_name, customer_state FROM customer_dimension TABLESAMPLE(0.5) WHERE customer_state='IL';
    customer_name    | customer_state
---------------------+----------------
 Amy Y. McNulty      | IL
 Daniel C. Nguyen    | IL
 Midori O. Greenwood | IL
 Meghan U. Lampert   | IL
 Tiffany Y. Lang     | IL
 Laura S. King       | IL
 Steve T. Nguyen     | IL
 Craig S. Webber     | IL
 Luigi A. Lewis      | IL
 Mark W. Williams    | IL
(10 rows)