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TRIGGER

CREATE
[DEFINER = { user | CURRENT_USER }]
TRIGGER trigger_name
{ BEFORE | AFTER }  { INSERT | UPDATE | DELETE }
ON tbl_name FOR EACH ROW
[{ FOLLOWS | PRECEDES } other_trigger_name]
trigger_body
INSERT activates the trigger through INSERT, LOAD DATA and REPLACE statements.
UPDATE activates the trigger through UPDATE statements.
DELETE activates the trigger through DELETE and REPLACE statements.
Cascaded foreign key actions do not activate triggers.
There must not be triggers for a given table that have the same trigger name and action time. For instance, you cannot have two BEFORE INSERT triggers for a table.
DROP TRIGGER [IF EXISTS] [schema_name.]trigger_name 

SET @sum=0;
DROP TABLE IF EXISTS account;
DROP TRIGGER IF EXISTS sumT;
CREATE TABLE account (amount DECIMAL(10,2));
CREATE TRIGGER sumT 
       BEFORE INSERT ON account
       FOR EACH ROW SET @sum = @sum + NEW.amount;
INSERT INTO account VALUES (300),(200);
SELECT @sum;