2.1 KiB
KEEP [esql-keep]
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):
- Complete field name (no wildcards)
- Partial wildcard expressions (for example:
fieldNam*) - Wildcard only (
*)
If a field matches two expressions with the same precedence, the rightmost expression wins.
Refer to the examples for illustrations of these precedence rules.
Examples
The columns are returned in the specified order:
:::{include} ../examples/docs.csv-spec/keep.md :::
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 :::
The asterisk wildcard (*) by itself translates to all columns that do not
match the other arguments.
This query will first return all columns with a name
that starts with h, followed by all other columns:
:::{include} ../examples/docs.csv-spec/keepDoubleWildcard.md :::
The following examples show how precedence rules work when a field name matches multiple expressions.
Complete field name has precedence over wildcard expressions:
:::{include} ../examples/docs.csv-spec/keepCompleteName.md :::
Wildcard expressions have the same priority, but last one wins (despite being less specific):
:::{include} ../examples/docs.csv-spec/keepWildcardPrecedence.md :::
A simple wildcard expression * has the lowest precedence.
Output order is determined by the other arguments:
:::{include} ../examples/docs.csv-spec/keepWildcardLowest.md :::