Keep

serverless: ga
stack: ga

The KEEP processing command enables you to specify what columns are returned and the order in which they are returned.

Syntax

KEEP columns

Parameters

columns : A comma-separated list of columns to keep. Supports wildcards. See below for the behavior in case an existing column matches multiple given wildcards or column names.

Description

The KEEP processing command enables you to specify what columns are returned and the order in which they are returned.

Precedence rules are applied when a field name matches multiple expressions. Fields are added in the order they appear. If one field matches multiple expressions, the following precedence rules apply (from highest to lowest priority):

1. Complete field name (no wildcards)
2. Partial wildcard expressions (for example: fieldNam*)
3. Wildcard only (*)

If a field matches two expressions with the same precedence, the rightmost expression wins.

Examples

The following examples show how to select columns and illustrate the wildcard precedence rules.

Specify column order

Columns are returned in the order they are listed:

:::{include} ../examples/docs.csv-spec/keep.md :::

Use wildcards to select columns

Rather than specify each column by name, you can use wildcards to return all columns with a name that matches a pattern:

:::{include} ../examples/docs.csv-spec/keepWildcard.md :::

Control ordering with wildcard and specific columns

The asterisk wildcard (*) by itself translates to all columns that do not match the other arguments. This query returns all columns with a name that starts with h, followed by all other columns:

:::{include} ../examples/docs.csv-spec/keepDoubleWildcard.md :::

Exact name takes precedence over wildcards

Complete field name has precedence over wildcard expressions:

:::{include} ../examples/docs.csv-spec/keepCompleteName.md :::

Rightmost wildcard wins when priority is equal

Wildcard expressions have the same priority, but the rightmost one wins (despite being less specific):

:::{include} ../examples/docs.csv-spec/keepWildcardPrecedence.md :::

Bare wildcard has lowest priority

A simple wildcard expression * has the lowest precedence. Output order is determined by the other arguments:

:::{include} ../examples/docs.csv-spec/keepWildcardLowest.md :::