MySQL insert data create trigger fill UUID field value

Catalog

1、 Create test table

2、 Trigger basic syntax

2.1、 Trigger Name

2.2、INSERT | UPDATE | DELETE

2.3、BEFORE | AFTER

2.4、 Table name

2.5、 Trigger body

2.6、FOR EACH ROW

3、 Create a trigger to insert data -BEFORE 

3.1 Insert a piece of data

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1、 Create test table

DROP TABLE IF EXISTS `test_uuid`;
CREATE TABLE `test_uuid`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT ' Primary key ',
  `uuid` varchar(36) CHARACTER SET utf8 COLLATE utf8_unicode_ci NULL DEFAULT NULL COMMENT 'uuid',
  `content` varchar(250) CHARACTER SET utf8 COLLATE utf8_unicode_ci NULL DEFAULT NULL COMMENT ' Content ',
  `create_time` datetime(0) NULL DEFAULT NULL COMMENT ' Creation time ',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8 COLLATE = utf8_unicode_ci ROW_FORMAT = Dynamic;

2、 Trigger basic syntax

The syntax is as follows ：

CREATE < Trigger Name > < BEFORE | AFTER >
<INSERT | UPDATE | DELETE >
ON < Table name > FOR EACH Row< Trigger body >

The grammar is as follows .

2.1、 Trigger Name

Trigger name , Triggers must have unique names in the current database . If you want to create in a specific database , The name should be preceded by the name of the database .

2.2、INSERT | UPDATE | DELETE

Triggering event , Used to specify the type of statement that activates the trigger .

Be careful ： The execution times of the three triggers are as follows .

INSERT： Activate trigger when a new row is inserted into the table . for example ,INSERT Of BEFORE Triggers can not only be MySQL Of INSERT Statement activation , Can also be LOAD DATA Statement activation .
DELETE： Activates the trigger when a row of data is deleted from the table , for example DELETE and REPLACE sentence .
UPDATE： Activates a trigger when a row of data in a table is changed , for example UPDATE sentence .

2.3、BEFORE | AFTER

BEFORE and AFTER, When the trigger is triggered , Indicates that the trigger is triggered before or after the statement that activates it . Verify whether the new data meets the conditions , Then use BEFORE Options ; If you want to make a few or more changes after the statement that activates the trigger executes , It is usually used AFTER Options .

2.4、 Table name

The name of the table associated with the trigger , This table must be permanent , Triggers cannot be associated with temporary tables or views . The trigger is activated only when the trigger event on this table occurs . The same table cannot have two triggers with the same trigger time and event . for example , For a data table , You can't have two at the same time BEFORE UPDATE trigger , But there can be one BEFORE UPDATE Trigger and a BEFORE INSERT trigger , Or a BEFORE UPDATE Trigger and a AFTER UPDATE trigger .

2.5、 Trigger body

Trigger action body , Contains the... To be executed when the trigger is activated MySQL sentence . If you want to execute multiple statements , You can use BEGIN…END Compound statement structure .

2.6、FOR EACH ROW

Generally, it refers to line level trigger , For each line affected by the trigger event, activate the action of the trigger . for example , Use INSERT Statement inserts multiple rows of data into a table , The trigger will execute the corresponding trigger action for each row of data insertion .

Be careful ： Each table supports INSERT、UPDATE and DELETE Of BEFORE And AFTER, So each table supports at most 6 Trigger . Only one trigger per event per table is allowed at a time . A single trigger cannot be associated with multiple events or tables .

in addition , stay MySQL in , If you need to view the existing triggers in the database , You can use SHOW TRIGGERS sentence .

3、 Create a trigger to insert data -BEFORE 

CREATE TRIGGER addUuid BEFORE INSERT ON `test`.`test_uuid`
FOR EACH ROW BEGIN
IF new.uuid = ''  OR new.uuid is NULL THEN SET new.uuid = UUID();
END IF;
END

3.1 Insert a piece of data

INSERT INTO `test`.`test_uuid`( `content`, `create_time`) VALUES ( ' View insert generation uuid', now());

You can see uuid Automatically filled .