[Solved] Oracle JOIN operation performance changes when swapping SELECT statements

How to optimize this SQL query?

In case you have your own slow SQL query, you can optimize it automatically here.

For the query above, the following recommendations will be helpful as part of the SQL tuning process.
You'll find 3 sections below:

  1. Description of the steps you can take to speed up the query.
  2. The optimal indexes for this query, which you can copy and create in your database.
  3. An automatically re-written query you can copy and execute in your database.
The optimization process and recommendations:
  1. 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.
  2. Use UNION ALL instead of UNION (query line: 9): Always use UNION ALL unless you need to eliminate duplicate records. By using UNION ALL, you'll avoid the expensive distinct operation the database applies when using a UNION clause.
Optimal indexes for this query:
CREATE INDEX user_objects_idx_object_name_object_type ON USER_OBJECTS (OBJECT_NAME,OBJECT_TYPE);
CREATE INDEX user_procedures_idx_object_name_procedure_name ON USER_PROCEDURES (OBJECT_NAME,PROCEDURE_NAME);
The optimized query:
SELECT
        1 
    FROM
        USER_PROCEDURES 
    WHERE
        USER_PROCEDURES.OBJECT_NAME = SUBSTR(UPPER('Client_Sys.Clear_Info'), 1, INSTR(UPPER('Client_Sys.Clear_Info'), '.') - 1) 
        AND USER_PROCEDURES.PROCEDURE_NAME = SUBSTR(UPPER('Client_Sys.Clear_Info'), INSTR(UPPER('Client_Sys.Clear_Info'), '.') + 1) 
    UNION
    SELECT
        1 
    FROM
        USER_OBJECTS 
    WHERE
        USER_OBJECTS.OBJECT_NAME = UPPER('Client_Sys.Clear_Info') 
        AND USER_OBJECTS.OBJECT_TYPE = 'PROCEDURE'

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