enh: optimize the error message when illegally modifying the column length

source/libs/parser/src/parUtil.c

@@ -138,7 +138,7 @@ static char* getSyntaxErrFormat(int32_t errCode) {
     case TSDB_CODE_PAR_CANNOT_DROP_PRIMARY_KEY:
       return "Primary timestamp column cannot be dropped";
     case TSDB_CODE_PAR_INVALID_MODIFY_COL:
-      return "Only binary/nchar column length could be modified";
+      return "Only binary/nchar column length could be modified, and the length can only be increased, not decreased";
     case TSDB_CODE_PAR_INVALID_TBNAME:
       return "Invalid tbname pseudo column";
     case TSDB_CODE_PAR_INVALID_FUNCTION_NAME:

source/util/src/terror.c

@@ -521,7 +521,7 @@ TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_TIMELINE_FUNC,      "Invalid timeline fu
 TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_PASSWD,             "Invalid password")
 TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_ALTER_TABLE,        "Invalid alter table statement")
 TAOS_DEFINE_ERROR(TSDB_CODE_PAR_CANNOT_DROP_PRIMARY_KEY,    "Primary timestamp column cannot be dropped")
-TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_MODIFY_COL,         "Only binary/nchar column length could be modified")
+TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_MODIFY_COL,         "Only binary/nchar column length could be modified, and the length can only be increased, not decreased")
 TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_TBNAME,             "Invalid tbname pseudo column")
 TAOS_DEFINE_ERROR(TSDB_CODE_PAR_INVALID_FUNCTION_NAME,      "Invalid function name")
 TAOS_DEFINE_ERROR(TSDB_CODE_PAR_COMMENT_TOO_LONG,           "Comment too long")