MySQL Order of Operations?

Is there a definitive place to find order of operations for mySQL statements? Is the below order correct?

FROM clause WHERE clause G开发者_C百科ROUP BY clause HAVING clause SELECT clause ORDER BY clause

If this is the case, can I use a term defined in the SELECT clase (select first_name as "f_name") within the group by clause?

Thanks!

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I assume you are interested in SELECT, according to the MySQL documentation the syntax is as follows

SELECT
[ALL | DISTINCT | DISTINCTROW ]
  [HIGH_PRIORITY]
  [STRAIGHT_JOIN]
  [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
  [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
  [ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
  [ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[PROCEDURE procedure_name(argument_list)]
[INTO OUTFILE 'file_name' export_options
  | INTO DUMPFILE 'file_name'
  | INTO var_name [, var_name]]
[FOR UPDATE | LOCK IN SHARE MODE]]

Yes, you can use columns defined with AS in the GROUP BY clause.

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I think Order By comes before Select (you can sort on a column you haven't selected), but Group By and Having come dead last for sure. Grouping requires knowledge of the entire result set, and you can only group on non-aggregate columns in the Select list (and you must group on ALL of them). Once the result set is grouped, Having is applied as a set of conditions to the grouped result set.

So, I think most engines, including MySQL, process as follows:

• Define domain source (FROM clause including JOINs)
• Filter (WHERE)
• Sort (ORDER BY)
• Project (SELECT)
• Group (GROUP BY)
• Filter again (HAVING)