[GitHub] [flink] slinkydeveloper commented on a change in pull request #17256: [FLINK-23385][table] Implement COALESCE function

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slinkydeveloper commented on a change in pull request #17256:
URL: https://github.com/apache/flink/pull/17256#discussion_r709199542



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File path: docs/data/sql_functions.yml
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@@ -516,7 +516,14 @@ conditional:
   - sql: NULLIF(value1, value2)
     description: Returns NULL if value1 is equal to value2; returns value1 
otherwise. E.g., NULLIF(5, 5) returns NULL; NULLIF(5, 0) returns 5.
   - sql: COALESCE(value1, value2 [, value3]*)
-    description: Returns the first value that is not NULL from value1, value2, 
.... E.g., COALESCE(NULL, 5) returns 5.
+    description: |
+      Coalesce specifies a series of expressions, and returns the first 
expression whose value is not null.
+
+      If all the expressions evaluate as null, coalesce returns a null value.
+      The return type of the coalesce function is the least common type among 
its arguments, and it's nullable if all its arguments are nullable.
+
+      E.g. COALESCE(NULL, "-") returns "-".
+      E.g. COALESCE(f0, f1, "-") returns the first non-null value among f0 and 
f1, if both are null returns "-".

Review comment:
       ![Screenshot 2021-09-15 at 15-40-41 System (Built-in) 
Functions](https://user-images.githubusercontent.com/6706544/133444161-2564c852-afd9-454a-a438-c8cd2dbcfb1a.png)
   
   Looks good to me




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