Other Support Rules

In addition to the support rules for SELECT statement elements, operators, items, and data types, there are some other restrictions and rules on the secondary engine usage, as shown in Table 1.

**Table 1** Other support rules
Rule	Description
Support for the aggregate function COUNT	INVALID_TYPE is not supported. Other data types are supported.
Support for the aggregate functions SUM and AVG	MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_TIMESTAMP, MYSQL_TYPE_STRING, or MYSQL_TYPE_VARCHAR are not supported.
Support for the aggregate functions MIN and MAX	MYSQL_TYPE_STRING or MYSQL_TYPE_VARCHAR are not supported.
Aggregate functions COUNT, SUM, AVG, MIN, and MAX not supporting the distinct parameter	Aggregate functions do not support parameters with distinct, for example, sum(distinct a) or sum(distinct (a+b)).
Support for HashJoin	Connection of 10 same data types is supported. The data types must be all signed numbers or all unsigned numbers. Connection of constant columns (for examples, column 1 as b in a view) is not supported.
Support for NestedLoopJoin	Only the scenario where the internal table uses the equality index scanning operator or the filtering and equality index scanning operator is supported.
Support for the equality index scanning operator	Primary key indexes, unique indexes, common indexes, and composite indexes are supported. Prefix indexes are not supported. For index conditions, only same data types are supported, constants or expressions are not supported.

Parent topic: Support for Execution Plans