7.1  Differences and similarities in Data Manipulation 
Language
Modifying the application to work with DB2 UDB can be a significant task in the 
conversion process. While a large portion of this step may encompass changing 
code to work with a different development environment, it is likely that additional 
time will be spent on testing the resulting code.
7.1.1  SELECT syntax
This section focuses on the SELECT statement syntax as it is supported in 
MySQL, and attempts to show how MySQL extensions to the SQL standard 
might be implemented in DB2 Version 8. Example 7 1 shows the MySQL syntax 
for the 
SELECT
 statement. A discussion of individual keywords follows.
Example 7 1   MySQL SELECT syntax
SELECT [STRAIGHT_JOIN]
[SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
[SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS] [HIGH_PRIORITY]
[DISTINCT | DISTINCTROW | ALL]
select_expression,...
[INTO {OUTFILE | DUMPFILE}  file_name  export_options]
[FROM table_references
[WHERE where_definition]
[GROUP BY {unsigned_integer | col_name | formula} [ASC | DESC], ...
[WITH ROLLUP]]
[HAVING where_definition]
[ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] ,...]
[LIMIT [offset,] row_count | row_count OFFSET offset]
[PROCEDURE procedure_name(argument_list)]
[FOR UPDATE | LOCK IN SHARE MODE]]
The 
STRAIGHT_JOIN 
keyword forces the MySQL optimizer to join tables in the 
specified order. In DB2 the join order is always determined by the optimizer. The 
optimizer choices can be limited by changing the default query optimization class 
using SET CURRENT QUERY OPTIMIZATION to a lower level. This may still not 
force the optimizer to evaluate the join order as given in the SQL statement. 
However, the DB2 cost based optimizer usually chooses the best access path 
for a given query. For additional information see 9.5.5,  SQL execution plan  on 
page 308.
The options prefixed with 
SQL_ 
are MySQL specific and do not require a DB2 
equivalent.
156 
MySQL to DB2 UDB Conversion Guide






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