[SPARK-28435][SQL] Support accepting the interval keyword in the schema string

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala

@@ -1926,6 +1926,7 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
       case ("decimal", precision :: Nil) => DecimalType(precision.getText.toInt, 0)
       case ("decimal", precision :: scale :: Nil) =>
         DecimalType(precision.getText.toInt, scale.getText.toInt)
+      case ("interval", Nil) => CalendarIntervalType
       case (dt, params) =>
         val dtStr = if (params.nonEmpty) s"$dt(${params.mkString(",")})" else dt
         throw new ParseException(s"DataType $dtStr is not supported.", ctx)

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/DataTypeParserSuite.scala

@@ -58,6 +58,7 @@ class DataTypeParserSuite extends SparkFunSuite {
   checkDataType("varchAr(20)", StringType)
   checkDataType("cHaR(27)", StringType)
   checkDataType("BINARY", BinaryType)
+  checkDataType("interval", CalendarIntervalType)
 
   checkDataType("array<doublE>", ArrayType(DoubleType, true))
   checkDataType("Array<map<int, tinYint>>", ArrayType(MapType(IntegerType, ByteType, true), true))

sql/catalyst/src/test/scala/org/apache/spark/sql/types/StructTypeSuite.scala

@@ -82,4 +82,9 @@ class StructTypeSuite extends SparkFunSuite {
     assert(7 == schema.treeString(0).split("\n").length)
     assert(7 == schema.treeString(-1).split("\n").length)
   }
+
+  test("interval keyword in schema string") {
+    val interval = "`a` INTERVAL"
+    assert(fromDDL(interval).toDDL === interval)
+  }
 }

sql/core/src/test/resources/sql-tests/inputs/cast.sql

@@ -56,3 +56,7 @@ SELECT HEX(CAST(-123L AS binary));
 DESC FUNCTION boolean;
 DESC FUNCTION EXTENDED boolean;
 -- TODO: migrate all cast tests here.
+
+-- cast string to interval and interval to string
+SELECT CAST('interval 3 month 1 hour' AS interval);
+SELECT CAST(interval 3 month 1 hour AS string);

sql/core/src/test/resources/sql-tests/results/cast.sql.out

@@ -1,5 +1,5 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 33
+-- Number of queries: 35
 
 
 -- !query 0
@@ -271,3 +271,19 @@ Extended Usage:
 
 Function: boolean
 Usage: boolean(expr) - Casts the value `expr` to the target data type `boolean`.
+
+
+-- !query 33
+SELECT CAST('interval 3 month 1 hour' AS interval)
+-- !query 33 schema
+struct<CAST(interval 3 month 1 hour AS INTERVAL):interval>
+-- !query 33 output
+interval 3 months 1 hours
+
+
+-- !query 34
+SELECT CAST(interval 3 month 1 hour AS string)
+-- !query 34 schema
+struct<CAST(interval 3 months 1 hours AS STRING):string>
+-- !query 34 output
+interval 3 months 1 hours