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;
+    }
 
 }

src/main/java/com/alibaba/druid/sql/dialect/mysql/parser/MySqlStatementParser.java

@@ -2688,6 +2688,14 @@ public class MySqlStatementParser extends SQLStatementParser {
         accept(Token.DATABASE);
 
         SQLCreateDatabaseStatement stmt = new SQLCreateDatabaseStatement(JdbcConstants.MYSQL);
+        
+        if (lexer.token() == Token.IF) {
+            lexer.nextToken();
+            accept(Token.NOT);
+            accept(Token.EXISTS);
+            stmt.setIfNotExists(true);
+        }
+        
         stmt.setName(this.exprParser.name());
 
         if (lexer.token() == Token.DEFAULT) {

src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java

@@ -1601,6 +1601,9 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Printab
     @Override
     public boolean visit(SQLCreateDatabaseStatement x) {
         print0(ucase ? "CREATE DATABASE " : "create database ");
+        if (x.isIfNotExists()) {
+            print0(ucase ? "IF NOT EXISTS " : "if not exists ");    
+        }
         x.getName().accept(this);
         return false;
     }