update

docs/sql-ref-syntax-ddl-alter-table.md

@@ -236,20 +236,30 @@ ALTER TABLE table_identifier DROP [ IF EXISTS ] partition_spec [PURGE]
 
 ### SET AND UNSET
 
-#### SET TABLE PROPERTIES
+#### SET PROPERTIES
 
 `ALTER TABLE SET` command is used for setting the table properties. If a particular property was already set, 
 this overrides the old value with the new one.
 
-`ALTER TABLE UNSET` is used to drop the table property. 
-
 ##### Syntax
 
 ```sql
--- Set Table Properties 
+-- Set Properties
 ALTER TABLE table_identifier SET TBLPROPERTIES ( key1 = val1, key2 = val2, ... )
+```
+
+#### UNSET PROPERTIES
+
+`ALTER TABLE UNSET` command is used to drop the table property.
 
--- Unset Table Properties
+**Note:** If the specified property key does not exist, when you use the v1 command and do not specify `IF EXISTS`,
+it will throw the error-condition `UNSET_NONEXISTENT_PROPERTIES` and finally `failed`,
+however regardless of whether `IF EXISTS` is set or not, the v2 command will ignore it and finally `succeed`.
+
+##### Syntax
+
+```sql
+-- Unset Properties
 ALTER TABLE table_identifier UNSET TBLPROPERTIES [ IF EXISTS ] ( key1, key2, ... )
 ```
 

sql/core/src/test/scala/org/apache/spark/sql/execution/command/v1/AlterTableUnsetTblPropertiesSuite.scala

@@ -62,6 +62,10 @@ trait AlterTableUnsetTblPropertiesSuiteBase extends command.AlterTableUnsetTblPr
     getTableProperties(tableIdent).getOrElse(key, null)
   }
 
+  /**
+   * When using the v1 command to unset `non-existent` properties, the command will
+   * throw the error-condition `"UNSET_NONEXISTENT_PROPERTIES` and finally `failed`
+   */
   test("alter table unset non-existent properties") {
     withNamespaceAndTable("ns", "tbl") { t =>
       sql(s"CREATE TABLE $t (col1 int, col2 string, a int, b int) $defaultUsing")

sql/core/src/test/scala/org/apache/spark/sql/execution/command/v2/AlterTableUnsetTblPropertiesSuite.scala

@@ -52,6 +52,10 @@ class AlterTableUnsetTblPropertiesSuite
     getTableMetadata(tableIdent).properties.asScala.toMap.getOrElse(key, null)
   }
 
+  /**
+   * When using the v2 command to unset `non-existent` properties,
+   * the command will ignore `non-existent` properties and finally succeed
+   */
   test("alter table unset non-existent properties") {
     withNamespaceAndTable("ns", "tbl") { t =>
       sql(s"CREATE TABLE $t (col1 int, col2 string, a int, b int) $defaultUsing")
@@ -60,8 +64,6 @@ class AlterTableUnsetTblPropertiesSuite
       sql(s"ALTER TABLE $t SET TBLPROPERTIES ('k1' = 'v1', 'k2' = 'v2', 'k3' = 'v3')")
       checkTblProps(tableIdent, Map("k1" -> "v1", "k2" -> "v2", "k3" -> "v3"))
 
-      // when using the v2 command, when unsetting `non-existent` properties,
-      // The command will ignore `non-existent` properties and finally succeed
       // property to unset does not exist
       sql(s"ALTER TABLE $t UNSET TBLPROPERTIES ('k3', 'k4')")
       checkTblProps(tableIdent, Map("k1" -> "v1", "k2" -> "v2"))