Support for SELECT Statement Elements

A complete set of SELECT statement elements is as follows. For details about the syntax of the SELECT statement, visit the official website of MySQL at https://dev.mysql.com/doc/refman/8.0/en/select.html.

SELECT
[ALL | DISTINCT | DISTINCTROW ]
[HIGH_PRIORITY]
[STRAIGHT_JOIN]
[SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
[SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
select_expr [, select_expr] ...
[into_option]
[FROM table_references
[PARTITION partition_list]]
[WHERE where_condition]
[GROUP BY {col_name | expr | position}, ... [WITH ROLLUP]]
[HAVING where_condition]
[WINDOW window_name AS (window_spec)
[, window_name AS (window_spec)] ...]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[into_option]
[FOR {UPDATE | SHARE}
[OF tbl_name [, tbl_name] ...]
[NOWAIT | SKIP LOCKED]
| LOCK IN SHARE MODE]
[into_option]

into_option: {
INTO OUTFILE 'file_name'
[CHARACTER SET charset_name]
export_options
| INTO DUMPFILE 'file_name'
| INTO var_name [, var_name] ...
}

Table 1 describes the support for each element in the SELECT statement.

**Table 1** Support for the SELECT Statement
SELECT Statement Element	Description	Supported or Not
[ALL \| DISTINCT \| DISTINCTROW]	DISTINCT and DISTINCTROW indicate that duplicate columns are returned. ALL (or not using ALL, DISTINCT and DISTINCTROW) indicates that all records are returned.	Only ALL is supported. DISTINCT or DISTINCTROW is not supported.
[HIGH_PRIORITY]	Serves for the optimizer and does not affect the execution result set.	This keyword applies to the MySQL optimizer and does not affect KOVAE's execution or judgment.
[STRAIGHT_JOIN]	Serves for the optimizer and does not affect the execution result set.	This keyword applies to the MySQL optimizer and does not affect KOVAE's execution or judgment.
[SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]	Serves for the optimizer and does not affect the execution result set.	This keyword applies to the MySQL optimizer and does not affect KOVAE's execution or judgment.
[SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]	Serves for the optimizer and does not affect the execution result set.	This keyword applies to the MySQL optimizer and does not affect KOVAE's execution or judgment.
select_expr [, select_expr] …	Indicates the expression of the SELECT list. KOVAE judges the type of each item and parameter, and performs recursive judgment on each parameter.	Some are supported. For details, see Support for Item Types.
[into_option]	Indicates that the result set is written to files on the server.	Not supported. This is not a common scenario.
[FROM table_references [PARTITION partition_list]]	Indicates the relationship between SQL-related tables and JOIN.	Some table access types are supported. For details, see Table 3. Only non-temporary tables are supported. Only InnoDB tables are supported. Full-text indexes are not supported. Partitioned tables are not supported.
[WHERE where_condition]	Indicates the expression of the WHERE condition. KOVAE judges the type of each item and parameter, and performs recursive judgment on each parameter.	Some are supported. For details, see Support for Item Types.
[GROUP BY {col_name \| expr \| position}, ... [WITH ROLLUP]]	Indicates the GROUP BY clause. KOVAE judges the type of each item and parameter, and performs recursive judgment on each parameter.	Some are supported. For details, see Support for Item Types.
[HAVING where_condition]	Indicates the expression of the HAVING condition. KOVAE judges the type of each item and parameter, and performs recursive judgment on each parameter.	Some are supported. For details, see Support for Item Types.
[WINDOW window_name AS (window_spec) [, window_name AS (window_spec)] ...]	Indicates window functions.	Not supported.
[ORDER BY {col_name \| expr \| position} [ASC \| DESC], ... [WITH ROLLUP]]	Indicates the ORDER BY clause. KOVAE judges the type of each item and parameter, and performs recursive judgment on each parameter.	Some are supported. For details, see Support for Item Types.
[LIMIT {[offset,] row_count \| row_count OFFSET offset}]	Indicates the LIMIT clause.	Supported.
[into_option]	Indicates that the result set is written to files on the server.	Not supported. This is not a common scenario.
[FOR {UPDATE \| SHARE} [OF tbl_name [, tbl_name] ...] [NOWAIT \| SKIP LOCKED] \| LOCK IN SHARE MODE]	Indicates that locking reads are performed on the queried data.	Not supported.
[into_option]	Indicates that the result set is written to files on the server.	Not supported. This is not a common scenario.

**Table 2** Support for other items
Item	Supported or Not
Statement type	Only the same type of statement (SELECT query) as SQLCOM_SELECT is supported. Other statement types such as UPDATE are not supported.
Union	Simple non-UNION SELECT statements are supported.
Number of primary tables/number of constant tables	In the query, the situation in which primary tables contain constant tables is not supported.
AGG row number estimation	Execution plans that have not fully evaluated AGG are not supported.
Querying the maximum number of fields	Query statement containing the number of fields greater than the value of MAX_FIELDS is not supported.
Query in which the optimizer determines an empty result set	If the optimizer has determined that the query result set must be an empty set, the query is not supported.
Character set	Only the UTF8MB4 character set is supported.

Only the first five table access types in Table 3 are supported.

**Table 3** Support for table access types
Table Access Type	Description	Supported or Not
JT_EQ_REF	Equality matching on the unique index	Supported
JT_REF	Equality matching on non-unique indexes	Supported
JT_ALL	Full table scan	Supported
JT_RANGE	Range scan	Supported
JT_INDEX_SCAN	Scan on leaf nodes of indexes	Supported
JT_SYSTEM	-	Not supported
JT_CONST	-	Not supported
JT_FT	-	Not supported
JT_REF_OR_NULL	-	Not supported
JT_INDEX_MERGE	-	Not supported

Parent topic: SQL Statement Specifications Supported by KOVAE