mysql sql parser support 'create database if not exists'

src/main/java/com/alibaba/druid/sql/ast/statement/SQLCreateDatabaseStatement.java

@@ -30,6 +30,8 @@ public class SQLCreateDatabaseStatement extends SQLStatementImpl {
     private String               collate;
 
     private List<SQLCommentHint> hints;
+    
+    protected boolean            ifNotExists = false;
 
     public SQLCreateDatabaseStatement(){
     }
@@ -77,5 +79,13 @@ public class SQLCreateDatabaseStatement extends SQLStatementImpl {
     public void setHints(List<SQLCommentHint> hints) {
         this.hints = hints;
     }
+    
+    public boolean isIfNotExists() {
+        return ifNotExists;
+    }
+    
+    public void setIfNotExists(boolean ifNotExists) {
+        this.ifNotExists = ifNotExists;
+    }
 
 }