[SPARK-24636][SQL] Type coercion of arrays for array_join function

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala

@@ -536,6 +536,13 @@ object TypeCoercion {
           case None => c
         }
 
+      case aj @ ArrayJoin(arr, d, nr) if !ArrayType(StringType).acceptsType(arr.dataType) &&
+        ArrayType.acceptsType(arr.dataType) =>
+        val containsNull = arr.dataType.asInstanceOf[ArrayType].containsNull
+        ImplicitTypeCasts.implicitCast(arr, ArrayType(StringType, containsNull))
+          .map(a => ArrayJoin(a, d, nr))
+          .getOrElse(aj)
+
       case m @ CreateMap(children) if m.keys.length == m.values.length &&
         (!haveSameType(m.keys) || !haveSameType(m.values)) =>
         val newKeys = if (haveSameType(m.keys)) {

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala

@@ -1237,6 +1237,7 @@ case class ArrayJoin(
 
   override def dataType: DataType = StringType
 
+  override def prettyName: String = "array_join"
 }
 
 /**

sql/core/src/test/resources/sql-tests/inputs/typeCoercion/native/arrayJoin.sql

@@ -0,0 +1,11 @@
+SELECT array_join(array(true, false), ', ');
+SELECT array_join(array(2Y, 1Y), ', ');
+SELECT array_join(array(2S, 1S), ', ');
+SELECT array_join(array(2, 1), ', ');
+SELECT array_join(array(2L, 1L), ', ');
+SELECT array_join(array(9223372036854775809, 9223372036854775808), ', ');
+SELECT array_join(array(2.0D, 1.0D), ', ');
+SELECT array_join(array(float(2.0), float(1.0)), ', ');
+SELECT array_join(array(date '2016-03-14', date '2016-03-13'), ', ');
+SELECT array_join(array(timestamp '2016-11-15 20:54:00.000', timestamp '2016-11-12 20:54:00.000'), ', ');
+SELECT array_join(array('a', 'b'), ', ');

sql/core/src/test/resources/sql-tests/results/typeCoercion/native/arrayJoin.sql.out

@@ -0,0 +1,90 @@
+-- Automatically generated by SQLQueryTestSuite
+-- Number of queries: 11
+
+
+-- !query 0
+SELECT array_join(array(true, false), ', ')
+-- !query 0 schema
+struct<array_join(array(true, false), , ):string>
+-- !query 0 output
+true, false
+
+
+-- !query 1
+SELECT array_join(array(2Y, 1Y), ', ')
+-- !query 1 schema
+struct<array_join(array(2, 1), , ):string>
+-- !query 1 output
+2, 1
+
+
+-- !query 2
+SELECT array_join(array(2S, 1S), ', ')
+-- !query 2 schema
+struct<array_join(array(2, 1), , ):string>
+-- !query 2 output
+2, 1
+
+
+-- !query 3
+SELECT array_join(array(2, 1), ', ')
+-- !query 3 schema
+struct<array_join(array(2, 1), , ):string>
+-- !query 3 output
+2, 1
+
+
+-- !query 4
+SELECT array_join(array(2L, 1L), ', ')
+-- !query 4 schema
+struct<array_join(array(2, 1), , ):string>
+-- !query 4 output
+2, 1
+
+
+-- !query 5
+SELECT array_join(array(9223372036854775809, 9223372036854775808), ', ')
+-- !query 5 schema
+struct<array_join(array(9223372036854775809, 9223372036854775808), , ):string>
+-- !query 5 output
+9223372036854775809, 9223372036854775808
+
+
+-- !query 6
+SELECT array_join(array(2.0D, 1.0D), ', ')
+-- !query 6 schema
+struct<array_join(array(2.0, 1.0), , ):string>
+-- !query 6 output
+2.0, 1.0
+
+
+-- !query 7
+SELECT array_join(array(float(2.0), float(1.0)), ', ')
+-- !query 7 schema
+struct<array_join(array(CAST(2.0 AS FLOAT), CAST(1.0 AS FLOAT)), , ):string>
+-- !query 7 output
+2.0, 1.0
+
+
+-- !query 8
+SELECT array_join(array(date '2016-03-14', date '2016-03-13'), ', ')
+-- !query 8 schema
+struct<array_join(array(DATE '2016-03-14', DATE '2016-03-13'), , ):string>
+-- !query 8 output
+2016-03-14, 2016-03-13
+
+
+-- !query 9
+SELECT array_join(array(timestamp '2016-11-15 20:54:00.000', timestamp '2016-11-12 20:54:00.000'), ', ')
+-- !query 9 schema
+struct<array_join(array(TIMESTAMP('2016-11-15 20:54:00.0'), TIMESTAMP('2016-11-12 20:54:00.0')), , ):string>
+-- !query 9 output
+2016-11-15 20:54:00, 2016-11-12 20:54:00
+
+
+-- !query 10
+SELECT array_join(array('a', 'b'), ', ')
+-- !query 10 schema
+struct<array_join(array(a, b), , ):string>
+-- !query 10 output
+a, b

sql/core/src/test/scala/org/apache/spark/sql/DataFrameFunctionsSuite.scala

@@ -552,6 +552,23 @@ class DataFrameFunctionsSuite extends QueryTest with SharedSQLContext {
     checkAnswer(
       df.selectExpr("array_join(x, delimiter, 'NULL')"),
       Seq(Row("a,b"), Row("a,NULL,b"), Row("")))
+
+    val idf = Seq(Seq(1, 2, 3)).toDF("x")
+
+    checkAnswer(
+      idf.select(array_join(idf("x"), ", ")),
+      Seq(Row("1, 2, 3"))
+    )
+    checkAnswer(
+      idf.selectExpr("array_join(x, ', ')"),
+      Seq(Row("1, 2, 3"))
+    )
+    intercept[AnalysisException] {
+      idf.selectExpr("array_join(x, 1)")
+    }
+    intercept[AnalysisException] {
+      idf.selectExpr("array_join(x, ', ', 1)")
+    }
   }
 
   test("array_min function") {