Add "SHOW '...' STATS" command back into parser

Somehow when upgrading the NanoDB parser to ANTLR4, I forgot to include
the SHOW STATS command.  This is essential for the storage lab, so of
course I added it back in as quickly as possible.

src/main/antlr4/edu/caltech/nanodb/sqlparse/NanoSQL.g4

@@ -43,6 +43,7 @@ commandNoSemicolon:
       | showTablesStmt
       | showPropsStmt
       | setPropStmt
+      | showSystemStatsStmt
       ;
 
 
@@ -204,6 +205,9 @@ rollbackTxnStmt:
 
 //============================================================================
 // Other utility statements
+//   SHOW PROPERTIES
+//   SET PROPERTY '...' = ...
+//   SHOW '...' STATS
 //   FLUSH
 //   CRASH
 //   EXIT (or QUIT)
@@ -215,6 +219,9 @@ showPropsStmt:
 setPropStmt:
         SET PROPERTY name=STRING_LITERAL '=' expression ;
 
+showSystemStatsStmt:
+        SHOW name=STRING_LITERAL STATS ;
+
 flushStmt:
         FLUSH ;
 

src/main/java/edu/caltech/nanodb/sqlparse/NanoSQLTranslator.java

@@ -5,6 +5,7 @@ import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.util.ArrayList;
 
+import edu.caltech.nanodb.commands.ShowSystemStatsCommand;
 import edu.caltech.nanodb.expressions.ArithmeticOperator;
 import edu.caltech.nanodb.expressions.BooleanOperator;
 import edu.caltech.nanodb.expressions.ColumnName;
@@ -166,6 +167,16 @@ public class NanoSQLTranslator extends NanoSQLBaseVisitor<Object> {
             (Expression) visit(ctx.expression()));
     }
 
+    @Override
+    public Object visitShowSystemStatsStmt(NanoSQLParser.ShowSystemStatsStmtContext ctx) {
+        String systemName = ctx.name.getText();
+
+        // Remove the quotes from around the subsystem name
+        systemName = systemName.substring(1, systemName.length() - 1);
+
+        return new ShowSystemStatsCommand(systemName);
+    }
+
     //=== TABLE/INDEX UTILITY COMMANDS =======================================
 
     @Override