• Alexander Barkov's avatar
    MDEV-16094 Crash when using AS OF with a stored function · 46be3198
    Alexander Barkov authored
    MDEV-16100 FOR SYSTEM_TIME erroneously resolves string user variables as transaction IDs
    
    Problem:
    
    Vers_history_point::resolve_unit() tested item->result_type() before
    item->fix_fields() was called.
    
    - Item_func_get_user_var::result_type() returned REAL_RESULT by default.
      This caused MDEV-16100.
    - Item_func_sp::result_type() crashed on assert.
      This caused MDEV-16094
    
    Changes:
    1. Adding item->fix_fields() into Vers_history_point::resolve_unit()
       before using data type specific properties of the history point
       expression.
    
    2. Adding a new virtual method Type_handler::Vers_history_point_resolve_unit()
    
    3. Implementing type-specific
       Type_handler_xxx::Type_handler::Vers_history_point_resolve_unit()
        in the way to:
        a. resolve temporal and general purpose string types to TIMESTAMP
        b. resolve BIT and general purpose INT types to TRANSACTION
        c. disallow use of non-relevant data type expressions in FOR SYSTEM_TIME
    
        Note, DOUBLE and DECIMAL data types are disallowed intentionally.
        - DOUBLE does not have enough precision to hold huge BIGINT UNSIGNED values
        - DECIMAL rounds on conversion to INT
        Both lack of precision and rounding might potentionally lead to
        very unpredictable results when a wrong transaction ID would be chosen.
        If one really wants dangerous use of DOUBLE and DECIMAL, explicit CAST
        can be used:
    
          FOR SYSTEM_TIME AS OF CAST(double_or_decimal AS UNSIGNED)
    
        QQ: perhaps DECIMAL(N,0) could still be allowed.
    
    4. Adding a new virtual method Item::type_handler_for_system_time(),
       to make HEX hybrids and bit literals work as TRANSACTION rather
       than TIMESTAMP.
    
    5. sql_yacc.yy: replacing the rule temporal_literal to "TIMESTAMP TEXT_STRING".
       Other temporal literals now resolve to TIMESTAMP through the new
       Type_handler methods. No special grammar needed. This removed
       a few shift/resolve conflicts.
       (TIMESTAMP related conflicts in "history_point:" will be removed separately)
    
    6. Removing the "timestamp_only" parameter from
       vers_select_conds_t::resolve_units() and Vers_history_point::resolve_unit().
       It was a hint telling that a table did not have any TRANSACTION-aware
       system time columns, so it's OK to resolve to TIMESTAMP in case of uncertainty.
       In the new reduction it works as follows:
       - the decision between TIMESTAMP and TRANSACTION is first made
         based only on the expression data type only
       - then, in case if the expression resolved to TRANSACTION, the table
         is checked if TRANSACTION-aware columns really exist.
       This way is safer against possible ALTER TABLE statements changing
       ROW START and ROW END columns from "BIGINT UNSIGNED" to "TIMESTAMP(x)"
       or the other way around.
    46be3198
table.cc 266 KB