120 lines
4.0 KiB
Markdown
120 lines
4.0 KiB
Markdown
---
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layout: default
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title: Limitations
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parent: SQL
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nav_order: 18
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---
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# Limitations
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The SQL plugin has the following limitations:
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## SELECT FROM WHERE
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### Select literal is not supported
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The select literal expression is not supported. For example, `Select 1` is not supported.
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Here's a link to the Github issue - [Issue #256](https://github.com/opensearch-project/sql/issues/256).
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### Where clause does not support arithmetic operations
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The `WHERE` clause does not support expressions. For example, `SELECT FlightNum FROM opensearch_dashboards_sample_data_flights where (AvgTicketPrice + 100) <= 1000` is not supported.
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Here's a link to the Github issue - [Issue #234](https://github.com/opensearch-project/sql/issues/234).
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### Aggregation over expression is not supported
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You can only apply aggregation on fields, aggregations can't accept an expression as a parameter. For example, `avg(log(age))` is not supported.
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Here's a link to the Github issue - [Issue #288](https://github.com/opensearch-project/sql/issues/288).
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### Conflict type in multiple index query
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Queries using wildcard index fail if the index has the field with a conflict type.
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For example, if you have two indices with field `a`:
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```
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POST conflict_index_1/_doc/
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{
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"a": {
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"b": 1
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}
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}
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POST conflict_index_2/_doc/
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{
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"a": {
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"b": 1,
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"c": 2
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}
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}
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```
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Then, the query fails because of the field mapping conflict. The query `SELECT * FROM conflict_index*` also fails for the same reason.
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```sql
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Error occurred in OpenSearch engine: Different mappings are not allowed for the same field[a]: found [{properties:{b:{type:long},c:{type:long}}}] and [{properties:{b:{type:long}}}] ",
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"details": "com.amazon.opensearch.sql.rewriter.matchtoterm.VerificationException: Different mappings are not allowed for the same field[a]: found [{properties:{b:{type:long},c:{type:long}}}] and [{properties:{b:{type:long}}}] \nFor more details, please send request for Json format to see the raw response from opensearch engine.",
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"type": "VerificationException
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```
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Here's a link to the Github issue - [Issue #445](https://github.com/opensearch-project/sql/issues/445).
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## Subquery in the FROM clause
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Subquery in the `FROM` clause in this format: `SELECT outer FROM (SELECT inner)` is supported only when the query is merged into one query. For example, the following query is supported:
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```sql
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SELECT t.f, t.d
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FROM (
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SELECT FlightNum as f, DestCountry as d
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FROM opensearch_dashboards_sample_data_flights
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WHERE OriginCountry = 'US') t
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```
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But, if the outer query has `GROUP BY` or `ORDER BY`, then it's not supported.
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## JOIN does not support aggregations on the joined result
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The `join` query does not support aggregations on the joined result.
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For example, e.g. `SELECT depo.name, avg(empo.age) FROM empo JOIN depo WHERE empo.id == depo.id GROUP BY depo.name` is not supported.
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Here's a link to the Github issue - [Issue 110](https://github.com/opensearch-project/sql/issues/110).
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## Pagination only supports basic queries
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The pagination query enables you to get back paginated responses.
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Currently, the pagination only supports basic queries. For example, the following query returns the data with cursor id.
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```json
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POST _opensearch/_sql/
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{
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"fetch_size" : 5,
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"query" : "SELECT OriginCountry, DestCountry FROM opensearch_dashboards_sample_data_flights ORDER BY OriginCountry ASC"
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}
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```
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The response in JDBC format with cursor id.
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```json
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{
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"schema": [
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{
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"name": "OriginCountry",
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"type": "keyword"
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},
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{
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"name": "DestCountry",
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"type": "keyword"
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}
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],
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"cursor": "d:eyJhIjp7fSwicyI6IkRYRjFaWEo1UVc1a1JtVjBZMmdCQUFBQUFBQUFCSllXVTJKVU4yeExiWEJSUkhsNFVrdDVXVEZSYkVKSmR3PT0iLCJjIjpbeyJuYW1lIjoiT3JpZ2luQ291bnRyeSIsInR5cGUiOiJrZXl3b3JkIn0seyJuYW1lIjoiRGVzdENvdW50cnkiLCJ0eXBlIjoia2V5d29yZCJ9XSwiZiI6MSwiaSI6ImtpYmFuYV9zYW1wbGVfZGF0YV9mbGlnaHRzIiwibCI6MTMwNTh9",
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"total": 13059,
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"datarows": [[
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"AE",
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"CN"
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]],
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"size": 1,
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"status": 200
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}
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```
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The query with `aggregation` and `join` does not support pagination for now.
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