For the query above, the following recommendations will be helpful as part of the SQL tuning process. You'll find 3 sections below:
Description of the steps you can take to speed up the query.
The optimal indexes for this query, which you can copy and create in your database.
An automatically re-written query you can copy and execute in your database.
The optimization process and recommendations:
Avoid Calling Functions With Indexed Columns (query line: 7): When a function is used directly on an indexed column, the database's optimizer won’t be able to use the index. For example, if the column `geom` is indexed, the index won’t be used as it’s wrapped with the function `ST_Y`. If you can’t find an alternative condition that won’t use a function call, a possible solution is to store the required value in a new indexed column.
Avoid Selecting Unnecessary Columns (query line: 2): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.
Optimal indexes for this query:
CREATE INDEX my_table_idx_my_date ON "my_table" ("my_date");
The optimized query:
my_table.my_date BETWEEN '2011-12-21' AND '2012-03-21'
AND ST_Y(ST_Centroid(my_table.geom)) > 0