[druid] branch master updated: recommendation for comparing strings and numbers (#12442)

[su...@apache.org]

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suneet pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/druid.git


The following commit(s) were added to refs/heads/master by this push:
     new c86c48203e recommendation for comparing strings and numbers (#12442)
c86c48203e is described below

commit c86c48203edf67a696a6e64c677a4792ff26079e
Author: Victoria Lim <vt...@users.noreply.github.com>
AuthorDate: Mon Apr 18 09:28:32 2022 -0700

    recommendation for comparing strings and numbers (#12442)
---
 docs/querying/sql-syntax.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/docs/querying/sql-syntax.md b/docs/querying/sql-syntax.md
index c6a6ffb1ed..5ad78065c5 100644
--- a/docs/querying/sql-syntax.md
+++ b/docs/querying/sql-syntax.md
@@ -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


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