始终在 SQL 中的最后一个条目之后将新数据插入表中

Question

I have several tables with a time unix and time mez column for identification. Those will be continuously filled with new data (every 60 seconds to be precise). I created a table, let's call it new_table from data of those tables. Now I want to update this new_table. But only with data of the other tables which are newer than the last entry of new_table.

So I don't have to overwrite new_table or collect all the data starting from row 1 again, since it supposed to run for years.

I tried some INSERT or UPDATE but I can't get my head around on how to define the SELECT and WHERE condition on which data should be updated. I'm very inexperienced in SQL. Thanks in advance!

See the following code on how I created new_table:

USE database; /* select database */

CREATE TABLE new_table
AS
    SELECT
        table1_1min.time_unix, table1_1min.time_mez,
        /* add power consumption in kW rounded to two decimal places */
        ROUND(table1.P + table2.P + table3.P, 2) AS total
    FROM 
        table1_1min, table2_1min, table3_1min
    /* make sure same time stamp is used in every row*/
    WHERE
        table1_1min.time_unix = table2_1min.time_unix 
        AND table1_1min.time_unix = table3_1min.time_unix
    ORDER BY 
        table1_1min.time_unix;

Answer 1

the most recent row in new_table can be found with

SELECT max(time_unix) FROM new_table

Knowing that, you can probably figure out how to get the new data. I'm not sure if you really want to create a new table each time you do this. TRUNCATE may be useful for you, but I think you want something like this:

INSERT INTO new_table ( time_unix, time_mez, total )
SELECT t1.time_unix, t1.time_mez, round(t1.p + t2.p + t3.p, 2) AS total
FROM table1_1min t1 JOIN table2_1min t2 ON (t1.time_unix = t2.time_unix) JOIN table3_1min t3 ON (t1.time_unix = t3.time_unix)
WHERE t1.time_unix > (SELECT max(time_unix) FROM new_table)