mysql stored procedure is slower 20 times than standard query

Question

i have 10 tables with same structure except table name.

i have a sp (stored procedure) defined as following:

 select * from table1 where (@param1 IS          


        

Answer 1

Just a guess:

When you run the query by hand, the expression WHERE ('test' IS NULL or COL1 = 'test') can be optimized when the query is being parsed. The parser can see that the string 'test' is not null, so it converts the test to WHERE COL1 = 'test'. And if there's an index on COL1 this will be used.

However, when you create a stored procedure, parsing occurs when the procedure is created. At that time, it doesn't know what @param will be, and has to implement the query as a sequential scan of the table.

Try changing your procedure to:

IF @param IS NULL
THEN BEGIN
  SELECT * FROM table1
  UNION ALL
  SELECT * FROM table2
  ...
END;
ELSE BEGIN
  SELECT * FROM table1 WHERE col1 = @param
  UNION ALL
  SELECT * FROM table2 WHERE col1 = @param
  ...
END;
END IF;

I don't have much experience with MySQL stored procedures, so I'm not sure that's all the right syntax.