How can easy select into temp table in MySQL? - mysql

Question

I need to create a temp table in one procedure.
Now my steps were:
1. DROP TEMPORARY TABLE if EXISTS
2. CREATE TEMPORARY TABLE
3. Do something with the table
4. DROP TEMPORARY TABLE if EXISTS
I do not want to create the temp table every time when I call the procedure.
I just want to truncate the temp table,but how to select some data into the existing temp table??
How to make the blow procedure run faster?
DROP PROCEDURE IF EXISTS `test`;
DELIMITER ;;
CREATE PROCEDURE `test`(IN type INT)
begin
DECLARE done INT DEFAULT 0;
DECLARE total INT DEFAULT 0;
DECLARE min_1 INT DEFAULT 0;
DECLARE min_10 INT DEFAULT 0;
DECLARE min_30 INT DEFAULT 0;
DECLARE tmp INT DEFAULT 0;
DECLARE cursor1 CURSOR FOR SELECT TIMESTAMPDIFF(MINUTE,time1,time2) as dif FROM t_test ;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
DROP TEMPORARY TABLE if EXISTS t_test;
CREATE TEMPORARY TABLE t_test AS (
SELECT optime as time1,dtime as time2
FROM tbmytest
WHERE thetpye = type);
OPEN cursor1;
REPEAT
FETCH cursor1 INTO tmp;
IF done = 1 THEN
close cursor1;
ELSE
SET total = total + 1;
IF tmp > 30 THEN
SET min_30 = min_30 + 1;
ELSEIF tmp > 10 THEN
SET min_10 = min_10 + 1;
ELSEIF tmp > -1 THEN
SET min_1 = min_1 + 1;
END IF;
END IF;
UNTIL done END REPEAT;
DROP TEMPORARY TABLE if EXISTS t_test;
SELECT min_1,min_10,min_30,total;
end;;
DELIMITER ;

Answer 1

Cursors are very, very slow. The temporary table may be not necessary.
You can achieve the same as the procedure in a single query. Use variables for this. Following query should do the job.
SELECT #min30, #min10, #min1 FROM (
SELECT #diff := TIMESTAMPDIFF(MINUTE,time1,time2),
CASE WHEN #diff > 30 THEN #min30 := #min30 + 1
WHEN #diff > 10 THEN #min10 := #min10 + 1
WHEN #diff > -1 THEN #min1 := #min1 + 1
END
FROM t_test
CROSS JOIN (SELECT #diff := NULL, #min1 := 0, #min10 := 0, #min30 := 0) var_init_subquery
) another_subquery_alias
I don't know if your question is simplified, meaning that you need the temporary table for other purposes, too. If it is so, instead of dropping and creating the table, you can also use a table with MEMORY engine and update it once in a while when needed.
CREATE TABLE my_special_temp_table
(min30 int, min10 int, min1 int)
ENGINE=MEMORY;
UPDATE my_special_temp_table
JOIN (
SELECT #min30 AS min30, #min10 AS min10, #min1 AS min1 FROM (
SELECT #diff := TIMESTAMPDIFF(MINUTE,time1,time2),
CASE WHEN #diff > 30 THEN #min30 := #min30 + 1
WHEN #diff > 10 THEN #min10 := #min10 + 1
WHEN #diff > -1 THEN #min1 := #min1 + 1
END
FROM t_test
CROSS JOIN (SELECT #diff := NULL, #min1 := 0, #min10 := 0, #min30 := 0) var_init_subquery
) another_subquery_alias
) t
SET my_special_temp_table.min30 = t.min30,
my_special_temp_table.min10 = t.min10,
my_special_temp_table.min1 = t.min1;