Z-Ordering is a technique to colocate related information in the same set of files. This co-locality is automatically used by Delta Lake on Databricks data-skipping algorithms to dramatically reduce the amount of data that needs to be read. Syntax for Z-ordering can be found here.
If you expect a column to be commonly used in query predicates and if that column has high cardinality (that is, a large number of distinct values) which might make it ineffective for PARTITIONing the table by, then use ZORDER BY instead (ex:- a table containing companies, dates where you might want to partition by company and z-order by date assuming that table collects data for several years)
You can specify multiple columns for ZORDER BY as a comma-separated list. However, the effectiveness of the locality drops with each additional column.
Important to note that you need statistics collected on columns that you Z-order by else data skipping won't take effect. Thus its important to reorder the table such that the Z-order by column(s) are in one of the first 32 columns or change the dataSkippingNumIndexedCols property
And if you learn best through visuals this is a great explainer video on Z-ordering on Delta Tables
