[SPARK-17364][SQL] Antlr lexer wrongly treats full qualified identifier as a decimal number token when parsing SQL string

## What changes were proposed in this pull request?

The Antlr lexer we use to tokenize a SQL string may wrongly tokenize a fully qualified identifier as a decimal number token. For example, table identifier `default.123_table` is wrongly tokenized as
```
default // Matches lexer rule IDENTIFIER
.123 // Matches lexer rule DECIMAL_VALUE
_TABLE // Matches lexer rule IDENTIFIER
```

The correct tokenization for `default.123_table` should be:
```
default // Matches lexer rule IDENTIFIER,
. // Matches a single dot
123_TABLE // Matches lexer rule IDENTIFIER
```

This PR fix the Antlr grammar so that it can tokenize fully qualified identifier correctly:
1. Fully qualified table name can be parsed correctly. For example, `select * from database.123_suffix`.
2. Fully qualified column name can be parsed correctly, for example `select a.123_suffix from a`.

### Before change

#### Case 1: Failed to parse fully qualified column name

```
scala> spark.sql("select a.123_column from a").show
org.apache.spark.sql.catalyst.parser.ParseException:
extraneous input '.123' expecting {<EOF>,
...
, IDENTIFIER, BACKQUOTED_IDENTIFIER}(line 1, pos 8)
== SQL ==
select a.123_column from a
--------^^^
```

#### Case 2: Failed to parse fully qualified table name
```
scala> spark.sql("select * from default.123_table")
org.apache.spark.sql.catalyst.parser.ParseException:
extraneous input '.123' expecting {<EOF>,
...
IDENTIFIER, BACKQUOTED_IDENTIFIER}(line 1, pos 21)

== SQL ==
select * from default.123_table
---------------------^^^
```

### After Change

#### Case 1: fully qualified column name, no ParseException thrown
```
scala> spark.sql("select a.123_column from a").show
```

#### Case 2: fully qualified table name, no ParseException thrown
```
scala> spark.sql("select * from default.123_table")
```

## How was this patch tested?

Unit test.

Author: Sean Zhong <seanzhong@databricks.com>

Closes #15006 from clockfly/SPARK-17364.

Author: clockfly

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

@@ -16,6 +16,30 @@
 
 grammar SqlBase;
 
+@members {
+  /**
+   * Verify whether current token is a valid decimal token (which contains dot).
+   * Returns true if the character that follows the token is not a digit or letter or underscore.
+   *
+   * For example:
+   * For char stream "2.3", "2." is not a valid decimal token, because it is followed by digit '3'.
+   * For char stream "2.3_", "2.3" is not a valid decimal token, because it is followed by '_'.
+   * For char stream "2.3W", "2.3" is not a valid decimal token, because it is followed by 'W'.
+   * For char stream "12.0D 34.E2+0.12 "  12.0D is a valid decimal token because it is folllowed
+   * by a space. 34.E2 is a valid decimal token because it is followed by symbol '+'
+   * which is not a digit or letter or underscore.
+   */
+  public boolean isValidDecimal() {
+    int nextChar = _input.LA(1);
+    if (nextChar >= 'A' && nextChar <= 'Z' || nextChar >= '0' && nextChar <= '9' ||
+      nextChar == '_') {
+      return false;
+    } else {
+      return true;
+    }
+  }
+}
+
 tokens {
     DELIMITER
 }
@@ -920,23 +944,22 @@ INTEGER_VALUE
     ;
 
 DECIMAL_VALUE
-    : DIGIT+ '.' DIGIT*
-    | '.' DIGIT+
+    : DECIMAL_DIGITS {isValidDecimal()}?
     ;
 
 SCIENTIFIC_DECIMAL_VALUE
-    : DIGIT+ ('.' DIGIT*)? EXPONENT
-    | '.' DIGIT+ EXPONENT
+    : DIGIT+ EXPONENT
+    | DECIMAL_DIGITS EXPONENT {isValidDecimal()}?
     ;
 
 DOUBLE_LITERAL
-    :
-    (INTEGER_VALUE | DECIMAL_VALUE | SCIENTIFIC_DECIMAL_VALUE) 'D'
+    : DIGIT+ EXPONENT? 'D'
+    | DECIMAL_DIGITS EXPONENT? 'D' {isValidDecimal()}?
     ;
 
 BIGDECIMAL_LITERAL
-    :
-    (INTEGER_VALUE | DECIMAL_VALUE | SCIENTIFIC_DECIMAL_VALUE) 'BD'
+    : DIGIT+ EXPONENT? 'BD'
+    | DECIMAL_DIGITS EXPONENT? 'BD' {isValidDecimal()}?
     ;
 
 IDENTIFIER
@@ -947,6 +970,11 @@ BACKQUOTED_IDENTIFIER
     : '`' ( ~'`' | '``' )* '`'
     ;
 
+fragment DECIMAL_DIGITS
+    : DIGIT+ '.' DIGIT*
+    | '.' DIGIT+
+    ;
+
 fragment EXPONENT
     : 'E' [+-]? DIGIT+
     ;

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

@@ -18,7 +18,7 @@ package org.apache.spark.sql.catalyst.parser
 
 import java.sql.{Date, Timestamp}
 
-import org.apache.spark.sql.catalyst.FunctionIdentifier
+import org.apache.spark.sql.catalyst.{FunctionIdentifier, TableIdentifier}
 import org.apache.spark.sql.catalyst.analysis.{UnresolvedAttribute, _}
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.PlanTest
@@ -518,4 +518,17 @@ class ExpressionParserSuite extends PlanTest {
     assertEqual("current_date", CurrentDate())
     assertEqual("current_timestamp", CurrentTimestamp())
   }
+
+  test("SPARK-17364, fully qualified column name which starts with number") {
+    assertEqual("123_", UnresolvedAttribute("123_"))
+    assertEqual("1a.123_", UnresolvedAttribute("1a.123_"))
+    // ".123" should not be treated as token of type DECIMAL_VALUE
+    assertEqual("a.123A", UnresolvedAttribute("a.123A"))
+    // ".123E3" should not be treated as token of type SCIENTIFIC_DECIMAL_VALUE
+    assertEqual("a.123E3_column", UnresolvedAttribute("a.123E3_column"))
+    // ".123D" should not be treated as token of type DOUBLE_LITERAL
+    assertEqual("a.123D_column", UnresolvedAttribute("a.123D_column"))
+    // ".123BD" should not be treated as token of type BIGDECIMAL_LITERAL
+    assertEqual("a.123BD_column", UnresolvedAttribute("a.123BD_column"))
+  }
 }

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

@@ -91,4 +91,17 @@ class TableIdentifierParserSuite extends SparkFunSuite {
       assert(TableIdentifier(nonReserved) === parseTableIdentifier(nonReserved))
     }
   }
+
+  test("SPARK-17364 table identifier - contains number") {
+    assert(parseTableIdentifier("123_") == TableIdentifier("123_"))
+    assert(parseTableIdentifier("1a.123_") == TableIdentifier("123_", Some("1a")))
+    // ".123" should not be treated as token of type DECIMAL_VALUE
+    assert(parseTableIdentifier("a.123A") == TableIdentifier("123A", Some("a")))
+    // ".123E3" should not be treated as token of type SCIENTIFIC_DECIMAL_VALUE
+    assert(parseTableIdentifier("a.123E3_LIST") == TableIdentifier("123E3_LIST", Some("a")))
+    // ".123D" should not be treated as token of type DOUBLE_LITERAL
+    assert(parseTableIdentifier("a.123D_LIST") == TableIdentifier("123D_LIST", Some("a")))
+    // ".123BD" should not be treated as token of type BIGDECIMAL_LITERAL
+    assert(parseTableIdentifier("a.123BD_LIST") == TableIdentifier("123BD_LIST", Some("a")))
+  }
 }