MySql split table on insert I am new so please go easy on me :)

I have the following table

CREATE TABLE `send_sms` (
    `sql_id` BIGINT(20) NOT NULL AUTO_INCREMENT,
    `momt` ENUM('MO','MT') NULL DEFAULT NULL,
    `sender` VARCHAR(20) NULL DEFAULT NULL,
    `receiver` VARCHAR(20) NULL DEFAULT NULL,
    `udhdata` BLOB NULL,
    `msgdata` TEXT NULL,
    `time` BIGINT(20) NULL DEFAULT NULL,
    `smsc_id` VARCHAR(255) NULL DEFAULT NULL,
    `service` VARCHAR(255) NULL DEFAULT NULL,
    `account` VARCHAR(255) NULL DEFAULT NULL,
    `id` BIGINT(20) NULL DEFAULT NULL,
    `sms_type` BIGINT(20) NULL DEFAULT NULL,
    `mclass` BIGINT(20) NULL DEFAULT NULL,
    `mwi` BIGINT(20) NULL DEFAULT NULL,
    `coding` BIGINT(20) NULL DEFAULT NULL,
    `compress` BIGINT(20) NULL DEFAULT NULL,
    `validity` BIGINT(20) NULL DEFAULT NULL,
    `deferred` BIGINT(20) NULL DEFAULT NULL,
    `dlr_mask` BIGINT(20) NULL DEFAULT NULL,
    `dlr_url` VARCHAR(255) NULL DEFAULT NULL,
    `pid` BIGINT(20) NULL DEFAULT NULL,
    `alt_dcs` BIGINT(20) NULL DEFAULT NULL,
    `rpi` BIGINT(20) NULL DEFAULT NULL,
    `charset` VARCHAR(255) NULL DEFAULT NULL,
    `boxc_id` VARCHAR(255) NULL DEFAULT NULL,
    `timestamp` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    `binfo` VARCHAR(255) NULL DEFAULT NULL,
    `meta_data` TEXT NULL,
    `priority` BIGINT(20) NULL DEFAULT NULL,
    `foreign_id` VARCHAR(255) NULL DEFAULT NULL,
    PRIMARY KEY (`sql_id`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
;


I have two different applications talking to each other via these tables. 

I would like to count the inserted rows (only 3 in below example, but could be 1000s at a time) and separate then into 3 other existing tables (same format)

So for Example:

INSERT INTO send_sms
( momt, sender, receiver, msgdata, sms_type, dlr_mask, dlr_url ) 
VALUES ( 'MT','1234', '447XXXXXXXX', 'Hello world4', 2, 27, 'test1' ),
( 'MT','Sender', '447XXXXXXXY', 'Hello world4', 2, 27, 'test2' ),
( 'MT','Sender', '447XXXXXXXY', 'Hello world4', 2, 27, 'test3' );


send_sms1 (would have test1)
send_sms2 (would have test2)
send_sms3 (would have test3)

Would need to be able to support if its not multiples of 3 example if its 10,000 rows send_sms1, send_sms2 should get 3,333 and send_sms3 should get 3,334 (doesn't matter which order). As this is a live system the table needs to be accessed at the same time (so during the move the table must be writable for other insert commands

I have tried things like like

INSERT INTO send_sms2(SELECT * FROM send_sms WHERE sql_id &gt;= (SELECT COUNT(*) FROM send_sms_dump)/2);



the above was just a test to split data- this worked however there isn't any delete so the data wasn't moved. Just 50K copied from the table to the other table


Please point me in the right direction so I can do some more research :)

Update thank you Rick James for the solution. 

I am now trying to create an update trigger

DELIMITER $$

CREATE TRIGGER my_trigger AFTER INSERT ON send_sms_dump
FOR EACH ROW
BEGIN
    -- Statement one
    INSERT INTO send_sms_dump2
    SELECT * FROM send_sms_dump
             WHERE sql_id % 3 = 0;
    -- Statement two
    INSERT INTO send_sms_dump3
    SELECT * FROM send_sms_dump
             WHERE sql_id % 3 = 1;
    -- More UPDATE statements
    INSERT INTO send_sms_dump4
    SELECT * FROM send_sms_dump
             WHERE sql_id % 3 = 2;
    -- More UPDATE statements
    DELETE FROM send_sms_dump;
END$$


I have the above the error is ... /* SQL Error (1442): Can't update table 'send_sms_dump' in stored function/trigger because it is already used by statement which invoked this stored function/trigger. */ ...

I am guessing its because of the delete command, i didn't want to drop the table as the third party application will be writing again to that table - let me know if i should post a new question :)

thanks guys
You have an AUTO_INCREMENT sql_id, so you have the rows numbered 1,2,3, 4,5,6, ... (unless you are using a clustering or Multi-Master setup that sets auto_increment_increment to something other than 1).

So, load the data into a table, then copy thirds into the three desired tables, and finally DROP the initial table.

INSERT INTO table_1
    SELECT * FROM table_all
             WHERE sql_id % 3 = 0;   -- 0 for table_1. 1 for table_2, 2 for table_3 


If you are adding to tables1/2/3, and they have an AUTO_INCREMENT, you can get unique ids by _skipping sql_id in the transfer:

INSERT INTO table_1 (b,c,d,e)
    SELECT b,c,d,e FROM table_all
             WHERE sql_id % 3 = 0;


This assumes the columns in table_all are 

sql_id,b,c,d,e


And table_1/2/3 have another column that is AUTO_INCREMENT.