[GitHub] [spark] zheniantoushipashi commented on a change in pull request #33201: [SPARK-36005][SQL] The canCast method of type of char/varchar is modified to be consistent with StringType

Thu, 05 Aug 2021 01:19:42 -0700 


zheniantoushipashi commented on a change in pull request #33201:
URL: https://github.com/apache/spark/pull/33201#discussion_r683234940



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File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
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@@ -54,38 +54,38 @@ object Cast {
 
     case (NullType, _) => true
 
-    case (_, StringType) => true
+    case (_, StringType | CharType(_) | VarcharType(_)) => true

Review comment:
       
   
   the method cast will change the type char/varchar to StringType,  so   cast 
method allows conversion from other types to CHAR/VARCHAR, although a warn 
message is printed.
   
   
   
![image](https://user-images.githubusercontent.com/3105102/128316157-26022c5e-5ac2-471a-aeff-42b0888986e5.png)
   
   
   
![image](https://user-images.githubusercontent.com/3105102/128316118-9dc15053-6a4e-48d0-aeeb-f0f3edf7c42b.png)
   
   
   in my application code,  I first use the canCast method to determine whether 
the type conversion can be performed before calling the cast method for 
conversion。
   
   
   
   **i  think the canCast method muse be consistent with Cast method**
   
   
   @cloud-fan  
   
   
   




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