115 lines
3.8 KiB
Plaintext
115 lines
3.8 KiB
Plaintext
[role="xpack"]
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[testenv="basic"]
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[[sql-index-patterns]]
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== Index patterns
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{es-sql} supports two types of patterns for matching multiple indices or tables:
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[[sql-index-patterns-multi]]
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[float]
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=== {es} multi-index
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The {es} notation for enumerating, including or excluding <<multi-index,multi index syntax>>
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is supported _as long_ as it is quoted or escaped as a table identifier.
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For example:
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["source","sql",subs="attributes,callouts,macros"]
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----
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include-tagged::{sql-specs}/docs/docs.csv-spec[showTablesEsMultiIndex]
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----
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Notice the pattern is surrounded by double quotes `"`. It enumerated `*` meaning all indices however
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it excludes (due to `-`) all indices that start with `l`.
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This notation is very convenient and powerful as it allows both inclusion and exclusion, depending on
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the target naming convention.
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The same kind of patterns can also be used to query multiple indices or tables.
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For example:
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["source","sql",subs="attributes,callouts,macros"]
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----
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include-tagged::{sql-specs}/docs/docs.csv-spec[fromTablePatternQuoted]
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----
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NOTE: There is the restriction that all resolved concrete tables have the exact same mapping.
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[[sql-index-patterns-like]]
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[float]
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=== SQL `LIKE` notation
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The common `LIKE` statement (including escaping if needed) to match a wildcard pattern, based on one `_`
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or multiple `%` characters.
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Using `SHOW TABLES` command again:
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["source","sql",subs="attributes,callouts,macros"]
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----
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include-tagged::{sql-specs}/docs/docs.csv-spec[showTablesLikeWildcard]
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----
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The pattern matches all tables that start with `emp`.
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This command supports _escaping_ as well, for example:
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["source","sql",subs="attributes,callouts,macros"]
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----
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include-tagged::{sql-specs}/docs/docs.csv-spec[showTablesLikeEscape]
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----
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Notice how now `emp%` does not match any tables because `%`, which means match zero or more characters,
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has been escaped by `!` and thus becomes an regular char. And since there is no table named `emp%`,
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an empty table is returned.
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In a nutshell, the differences between the two type of patterns are:
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[cols="^h,^,^"]
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|===
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s|Feature
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s|Multi index
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s|SQL `LIKE`
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| Type of quoting | `"` | `'`
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| Inclusion | Yes | Yes
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| Exclusion | Yes | No
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| Enumeration | Yes | No
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| One char pattern | No | `_`
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| Multi char pattern | `*` | `%`
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| Escaping | No | `ESCAPE`
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|===
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Which one to use, is up to you however try to stick to the same one across your queries for consistency.
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NOTE: As the query type of quoting between the two patterns is fairly similar (`"` vs `'`), {es-sql} _always_
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requires the keyword `LIKE` for SQL `LIKE` pattern.
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[[sql-index-frozen]]
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== Frozen Indices
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{es} <<frozen-indices, frozen indices>> are a useful and powerful tool for hot/warm architecture introduced in {es} 6.6,
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essentially by trading speed for memory.
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{es-sql} supports frozen indices and similar to {es}, due to their performance characteristics, allows searches on them only
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when explicitly told so by user - in other words, by default, frozen indices are not included in searches.
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One can toggle the use of frozen indices through:
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dedicated configuration parameter::
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Set to `true` properties `index_include_frozen` in the <<sql-rest>> or `index.include.frozen` in the drivers to include frozen indices.
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dedicated keyword::
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Explicitly perform the inclusion through the dedicated `FROZEN` keyword in the `FROM` clause or `INCLUDE FROZEN` in the `SHOW` commands:
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["source","sql",subs="attributes,callouts,macros"]
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----
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include-tagged::{sql-specs}/docs/docs.csv-spec[showTablesIncludeFrozen]
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----
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["source","sql",subs="attributes,callouts,macros"]
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----
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include-tagged::{sql-specs}/docs/docs.csv-spec[fromTableIncludeFrozen]
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----
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Unless enabled, frozen indices are completely ignored; it is as if they do not exist and as such, queries ran against them are likely to fail. |