Apache
/
druid
mirror of https://github.com/apache/druid.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

recommendation for comparing strings and numbers (#12442)

This commit is contained in:
Victoria Lim 2022-04-18 09:28:32 -07:00 committed by GitHub
parent 5167d328b1
commit c86c48203e
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 15 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
docs/querying/sql-syntax.md
View File

@ -67,6 +67,21 @@ The WHERE clause refers to columns in the FROM table, and will be translated to
WHERE clause can also reference a subquery, like `WHERE col1 IN (SELECT foo FROM ...)`. Queries like this are executed
as a join on the subquery, described in the [Query translation](sql-translation.md#subqueries) section.
Strings and numbers can be compared in the WHERE clause of a SQL query through implicit type conversion.
For example, you can evaluate `WHERE stringDim = 1` for a string-typed dimension named `stringDim`.
However, for optimal performance, you should explicitly cast the reference number as a string when comparing against a string dimension:
```
WHERE stringDim = '1'
```
Similarly, if you compare a string-typed dimension with reference to an array of numbers, cast the numbers to strings:
```
WHERE stringDim IN ('1', '2', '3')
```
Note that explicit type casting does not lead to significant performance improvement when comparing strings and numbers involving numeric dimensions since numeric dimensions are not indexed.
## GROUP BY
The GROUP BY clause refers to columns in the FROM table. Using GROUP BY, DISTINCT, or any aggregation functions will