include limitation of LIKE when it works with non-binary collation (#…

…15352)
pingcap · Nov 16, 2023 · 68e00ec · 68e00ec
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diff --git a/character-set-and-collation.md b/character-set-and-collation.md
@@ -113,6 +113,8 @@ SHOW COLLATION;
 > **Warning:**
 >
 > TiDB incorrectly treats latin1 as a subset of utf8. This can lead to unexpected behaviors when you store characters that differ between latin1 and utf8 encodings. It is strongly recommended to the utf8mb4 character set. See [TiDB #18955](https://github.com/pingcap/tidb/issues/18955) for more details.
+>
+> If the predicates include `LIKE` for string prefixes, such as `LIKE 'prefix%'`, and the target column is set to a non-binary collation (the suffix does not end with `_bin`), the optimizer currently cannot convert this predicate into a range scan. Instead, it performs a full scan. As a result, such SQL queries might lead to unexpected resource consumption.
 
 > **Note:**
 >

diff --git a/character-set-gbk.md b/character-set-gbk.md
@@ -98,6 +98,8 @@ In the above table, the result of `SELECT HEX('a');` in the `utf8mb4` byte set i
 
 - Currently, for binary characters of the `ENUM` and `SET` types, TiDB deals with them as the `utf8mb4` character set.
 
+- If the predicates include `LIKE` for string prefixes, such as `LIKE 'prefix%'`, and the target column is set to a GBK collation (either `gbk_bin` or `gbk_chinese_ci`), the optimizer currently cannot convert this predicate into a range scan. Instead, it performs a full scan. As a result, such SQL queries might lead to unexpected resource consumption.
+
 ## Component compatibility
 
 - Currently, TiFlash does not support the GBK character set.