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da5392134f
* Enforce an invariant in our dependency checker so that logical plans never have duplicate output attribute names or ids. * Fix ROW to not produce columns with duplicate names. * Fix ResolveUnionTypes to not create multiple synthetic field attributes for the same union type. * Add tests for commands using the same column name more than once. * Update docs w.r.t. how commands behave if they are used with duplicate column names.
78 lines
2.1 KiB
Text
78 lines
2.1 KiB
Text
[discrete]
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[[esql-eval]]
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=== `EVAL`
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The `EVAL` processing command enables you to append new columns with calculated
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values.
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**Syntax**
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[source,esql]
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----
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EVAL [column1 =] value1[, ..., [columnN =] valueN]
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----
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*Parameters*
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`columnX`::
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The column name.
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If a column with the same name already exists, the existing column is dropped.
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If a column name is used more than once, only the rightmost duplicate creates a column.
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`valueX`::
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The value for the column. Can be a literal, an expression, or a
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<<esql-functions,function>>. Can use columns defined left of this one.
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*Description*
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The `EVAL` processing command enables you to append new columns with calculated
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values. `EVAL` supports various functions for calculating values. Refer to
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<<esql-functions,Functions>> for more information.
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*Examples*
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[source.merge.styled,esql]
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----
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include::{esql-specs}/eval.csv-spec[tag=eval]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/eval.csv-spec[tag=eval-result]
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|===
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If the specified column already exists, the existing column will be dropped, and
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the new column will be appended to the table:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/eval.csv-spec[tag=evalReplace]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/eval.csv-spec[tag=evalReplace-result]
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|===
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Specifying the output column name is optional. If not specified, the new column
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name is equal to the expression. The following query adds a column named
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`height*3.281`:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/eval.csv-spec[tag=evalUnnamedColumn]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/eval.csv-spec[tag=evalUnnamedColumn-result]
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|===
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Because this name contains special characters, <<esql-identifiers,it needs to be
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quoted>> with backticks (+{backtick}+) when using it in subsequent commands:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/eval.csv-spec[tag=evalUnnamedColumnStats]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/eval.csv-spec[tag=evalUnnamedColumnStats-result]
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|===
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