[fix](Nereids) Add varchar literal compare (#15672)

support "1" = "123"

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/literal/Literal.java

@@ -139,7 +139,11 @@ public abstract class Literal extends Expression implements LeafExpression, Comp
 
         DataType oType = other.getDataType();
         DataType type = getDataType();
-        if (!type.equals(oType)) {
+
+        if (type.isVarcharType() && oType.isVarcharType()) {
+            // VarChar type can be different, e.g., VarChar(1) = VarChar(2)
+            return StringUtils.compare((String) getValue(), (String) other.getValue());
+        } else if (!type.equals(oType)) {
             throw new RuntimeException("data type not equal!");
         } else if (type.isBooleanType()) {
             return Boolean.compare((boolean) getValue(), (boolean) other.getValue());

regression-test/suites/nereids_syntax_p0/function.groovy

@@ -103,5 +103,10 @@ suite("nereids_function") {
         sql "select convert_to('abc', cast(number as varchar)) from numbers('number'='1')"
         exception "must be a constant"
     }
+
+    test {
+        sql """select "1" == "123", "%%" == "%%" """
+        result([[false, true]])
+    }
 }