mirror of https://github.com/apache/druid.git
89 lines
2.6 KiB
Markdown
89 lines
2.6 KiB
Markdown
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A filter is a JSON object indicating which rows of data should be included in the computation for a query. It’s essentially the equivalent of the WHERE clause in SQL. Druid supports the following types of filters.
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### Selector filter
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The simplest filter is a selector filter. The selector filter will match a specific dimension with a specific value. Selector filters can be used as the base filters for more complex Boolean expressions of filters.
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The grammar for a SELECTOR filter is as follows:
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<code>"filter": {
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"type": "selector",
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"dimension": <dimension_string>,
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"value": <dimension_value_string>
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}
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</code>
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This is the equivalent of `WHERE <dimension_string> = '<dimension_value_string>'`.
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### Regular expression filter
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The regular expression filter is similar to the selector filter, but using regular expressions. It matches the specified dimension with the given pattern. The pattern can be any standard [Java regular expression](http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html).
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<code>"filter": {
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"type": "regex",
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"dimension": <dimension_string>,
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"pattern": <pattern_string>
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}
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</code>
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### Logical expression filters
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#### AND
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The grammar for an AND filter is as follows:
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<code>"filter": {
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"type": "and",
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"fields": [<filter>, <filter>, ...]
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}
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</code>
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The filters in fields can be any other filter defined on this page.
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#### OR
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The grammar for an OR filter is as follows:
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<code>"filter": {
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"type": "or",
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"fields": [<filter>, <filter>, ...]
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}
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</code>
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The filters in fields can be any other filter defined on this page.
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#### NOT
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The grammar for a NOT filter is as follows:
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<code>"filter": {
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"type": "not",
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"field": <filter>
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}
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</code>
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The filter specified at field can be any other filter defined on this page.
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### JavaScript filter
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The JavaScript filter matches a dimension against the specified JavaScript function predicate. The filter matches values for which the function returns true.
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The function takes a single argument, the dimension value, and returns either true or false.
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<code>{
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"type" : "javascript",
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"dimension" : <dimension_string>,
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"function" : "function(value) { <...> }"
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}
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</code>
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**Example**
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The following matches any dimension values for the dimension `name` between `'bar'` and `'foo'`
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<code>{
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"type" : "javascript",
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"dimension" : "name",
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"function" : "function(x) { return(x >= 'bar' && x <= 'foo') }"
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}
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</code>
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