db2 sql parser support concat binary operator

src/main/java/com/alibaba/druid/sql/dialect/db2/parser/DB2Lexer.java

@@ -37,6 +37,7 @@ public class DB2Lexer extends Lexer {
         map.put("ONLY", Token.ONLY);
         map.put("OPTIMIZE", Token.OPTIMIZE);
         map.put("OF", Token.OF);
+        map.put("CONCAT", Token.CONCAT);
         
         DEFAULT_DB2_KEYWORDS = new Keywords(map);
     }

src/main/java/com/alibaba/druid/sql/dialect/db2/visitor/DB2OutputVisitor.java

@@ -17,6 +17,7 @@ package com.alibaba.druid.sql.dialect.db2.visitor;
 
 import com.alibaba.druid.sql.ast.SQLObject;
 import com.alibaba.druid.sql.ast.SQLOrderBy;
+import com.alibaba.druid.sql.ast.expr.SQLBinaryOperator;
 import com.alibaba.druid.sql.ast.statement.SQLSelect;
 import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
 import com.alibaba.druid.sql.dialect.db2.ast.stmt.DB2SelectQueryBlock;
@@ -91,4 +92,12 @@ public class DB2OutputVisitor extends SQLASTOutputVisitor implements DB2ASTVisit
     public void endVisit(DB2ValuesStatement x) {
 
     }
+    
+    protected void printOperator(SQLBinaryOperator operator) {
+        if (operator == SQLBinaryOperator.Concat) {
+            print0(ucase ? "CONCAT" : "concat");
+        } else {
+            print0(ucase ? operator.name : operator.name_lcase);
+        }
+    }
 }

src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java

@@ -1223,7 +1223,7 @@ public class SQLExprParser extends SQLParser {
 
             expr = new SQLBinaryOpExpr(expr, SQLBinaryOperator.Add, rightExp, getDbType());
             expr = additiveRest(expr);
-        } else if (lexer.token() == Token.BARBAR) {
+        } else if (lexer.token() == Token.BARBAR || lexer.token() == Token.CONCAT) {
             lexer.nextToken();
             SQLExpr rightExp = multiplicative();
             expr = new SQLBinaryOpExpr(expr, SQLBinaryOperator.Concat, rightExp, getDbType());

src/main/java/com/alibaba/druid/sql/parser/Token.java

@@ -277,6 +277,8 @@ public enum Token {
     FORMAT("FORMAT"),
     QUALIFY("QUALIFY"),
     MOD("MOD"),
+    
+    CONCAT("CONCAT"), // DB2
 
     LPAREN("("), 
     RPAREN(")"), 

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

@@ -329,7 +329,7 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Printab
             } else {
                 print0(" ");
             }
-            print0(ucase ? x.getOperator().name : x.getOperator().name_lcase);
+            printOperator(x.getOperator());
             print0(" ");
         }
 
@@ -342,6 +342,10 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Printab
         return false;
     }
 
+    protected void printOperator(SQLBinaryOperator operator) {
+        print0(ucase ? operator.name : operator.name_lcase);
+    }
+
     private void visitorBinaryRight(SQLBinaryOpExpr x) {
         if (isPrettyFormat() && x.getRight().hasBeforeComment()) {
             printlnComments(x.getRight().getBeforeCommentsDirect());