[SPARK-19518][SQL] IGNORE NULLS in first / last in SQL

## What changes were proposed in this pull request?

This PR proposes to add `IGNORE NULLS` keyword in `first`/`last` in Spark's parser likewise http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions057.htm.  This simply maps the keywords to existing `ignoreNullsExpr`.

**Before**

```scala
scala> sql("select first('a' IGNORE NULLS)").show()
```

```
org.apache.spark.sql.catalyst.parser.ParseException:
extraneous input 'NULLS' expecting {')', ','}(line 1, pos 24)

== SQL ==
select first('a' IGNORE NULLS)
------------------------^^^

  at org.apache.spark.sql.catalyst.parser.ParseException.withCommand(ParseDriver.scala:210)
  at org.apache.spark.sql.catalyst.parser.AbstractSqlParser.parse(ParseDriver.scala:112)
  at org.apache.spark.sql.execution.SparkSqlParser.parse(SparkSqlParser.scala:46)
  at org.apache.spark.sql.catalyst.parser.AbstractSqlParser.parsePlan(ParseDriver.scala:66)
  at org.apache.spark.sql.SparkSession.sql(SparkSession.scala:622)
  ... 48 elided
```

**After**

```scala
scala> sql("select first('a' IGNORE NULLS)").show()
```

```
+--------------+
|first(a, true)|
+--------------+
|             a|
+--------------+
```

## How was this patch tested?

Unit tests in `ExpressionParserSuite`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #17566 from HyukjinKwon/SPARK-19518.

sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBase.g4

@@ -552,6 +552,8 @@ primaryExpression
     | CASE whenClause+ (ELSE elseExpression=expression)? END                                   #searchedCase
     | CASE value=expression whenClause+ (ELSE elseExpression=expression)? END                  #simpleCase
     | CAST '(' expression AS dataType ')'                                                      #cast
+    | FIRST '(' expression (IGNORE NULLS)? ')'                                                 #first
+    | LAST '(' expression (IGNORE NULLS)? ')'                                                  #last
     | constant                                                                                 #constantDefault
     | ASTERISK                                                                                 #star
     | qualifiedName '.' ASTERISK                                                               #star
@@ -710,7 +712,7 @@ nonReserved
     | VIEW | REPLACE
     | IF
     | NO | DATA
-    | START | TRANSACTION | COMMIT | ROLLBACK
+    | START | TRANSACTION | COMMIT | ROLLBACK | IGNORE
     | SORT | CLUSTER | DISTRIBUTE | UNSET | TBLPROPERTIES | SKEWED | STORED | DIRECTORIES | LOCATION
     | EXCHANGE | ARCHIVE | UNARCHIVE | FILEFORMAT | TOUCH | COMPACT | CONCATENATE | CHANGE
     | CASCADE | RESTRICT | BUCKETS | CLUSTERED | SORTED | PURGE | INPUTFORMAT | OUTPUTFORMAT
@@ -836,6 +838,7 @@ TRANSACTION: 'TRANSACTION';
 COMMIT: 'COMMIT';
 ROLLBACK: 'ROLLBACK';
 MACRO: 'MACRO';
+IGNORE: 'IGNORE';
 
 IF: 'IF';
 

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

@@ -31,6 +31,7 @@ import org.apache.spark.sql.AnalysisException
 import org.apache.spark.sql.catalyst.{FunctionIdentifier, TableIdentifier}
 import org.apache.spark.sql.catalyst.analysis._
 import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.expressions.aggregate.{First, Last}
 import org.apache.spark.sql.catalyst.parser.SqlBaseParser._
 import org.apache.spark.sql.catalyst.plans._
 import org.apache.spark.sql.catalyst.plans.logical._
@@ -1022,6 +1023,22 @@ class AstBuilder extends SqlBaseBaseVisitor[AnyRef] with Logging {
     Cast(expression(ctx.expression), visitSparkDataType(ctx.dataType))
   }
 
+  /**
+   * Create a [[First]] expression.
+   */
+  override def visitFirst(ctx: FirstContext): Expression = withOrigin(ctx) {
+    val ignoreNullsExpr = ctx.IGNORE != null
+    First(expression(ctx.expression), Literal(ignoreNullsExpr)).toAggregateExpression()
+  }
+
+  /**
+   * Create a [[Last]] expression.
+   */
+  override def visitLast(ctx: LastContext): Expression = withOrigin(ctx) {
+    val ignoreNullsExpr = ctx.IGNORE != null
+    Last(expression(ctx.expression), Literal(ignoreNullsExpr)).toAggregateExpression()
+  }
+
   /**
    * Create a (windowed) Function expression.
    */

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

@@ -21,6 +21,7 @@ import java.sql.{Date, Timestamp}
 import org.apache.spark.sql.catalyst.FunctionIdentifier
 import org.apache.spark.sql.catalyst.analysis.{UnresolvedAttribute, _}
 import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.expressions.aggregate.{First, Last}
 import org.apache.spark.sql.catalyst.plans.PlanTest
 import org.apache.spark.sql.types._
 import org.apache.spark.unsafe.types.CalendarInterval
@@ -549,4 +550,11 @@ class ExpressionParserSuite extends PlanTest {
     val complexName2 = FunctionIdentifier("ba``r", Some("fo``o"))
     assertEqual(complexName2.quotedString, UnresolvedAttribute("fo``o.ba``r"))
   }
+
+  test("SPARK-19526 Support ignore nulls keywords for first and last") {
+    assertEqual("first(a ignore nulls)", First('a, Literal(true)).toAggregateExpression())
+    assertEqual("first(a)", First('a, Literal(false)).toAggregateExpression())
+    assertEqual("last(a ignore nulls)", Last('a, Literal(true)).toAggregateExpression())
+    assertEqual("last(a)", Last('a, Literal(false)).toAggregateExpression())
+  }
 }