MySQL after insert trigger get auto incremed value, update field value after insert gives “Unknown column” error

问题

I am trying to figure out make a trigger to assign the value of the auto incremented 'ID' primary key field that is auto generated upon insert to another field 'Sort_Placement' so they are the same after insert.

If you are wondering why I am doing this, 'Sort_Placement' is used as a sort value in a table that can be changed but by default the record is added to the bottom of the table

Table Data

`ID` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
`Account_Num` mediumint(8) unsigned NOT NULL,
`Product_Num` mediumint(8) unsigned NOT NULL,
`Sort_Placement` mediumint(8) unsigned DEFAULT NULL,
`Order_Qty_C` smallint(6) NOT NULL DEFAULT '0',
`Order_Qty_B` smallint(6) NOT NULL DEFAULT '0',
`Discount` decimal(6,2) NOT NULL DEFAULT '0.00',
PRIMARY KEY (`ID`),
UNIQUE KEY `ID_UNIQUE` (`ID`)

After Insert Trigger

CREATE 
TRIGGER `order_guide_insert_trigger`
AFTER INSERT ON `order_guide`
FOR EACH ROW
    BEGIN
    IF Sort_Placement IS NULL THEN
        SET Sort_Placement = NEW.ID;
    END IF;
END;

I have tried a bunch of combinations of using the "NEW" prefix with no luck. For example putting the NEW prefix before each field name.

Trying it out

INSERT INTO `order_guide` (`Account_Num`, `Product_Num`) VALUES ('5966', '3');

Insert Error

ERROR 1054: Unknown column 'Sort_Placement' in 'field list'

回答1:

This seems like a bit of a hack job but I was able to get it working using the LAST_INSERT_ID() function built into MySQL.

CREATE TRIGGER `order_guide_insert_trigger`
BEFORE INSERT ON `order_guide`
FOR EACH ROW 
BEGIN
    IF NEW.Sort_Placement IS NULL THEN
        SET NEW.Sort_Placement = LAST_INSERT_ID() + 1;
    END IF;
END;

This also works and seems to work

CREATE TRIGGER `order_guide_insert_trigger`
BEFORE INSERT ON `order_guide`
FOR EACH ROW 
BEGIN
    IF NEW.Sort_Placement IS NULL THEN
        SET NEW.Sort_Placement = (SELECT ID FROM order_Guide ORDER BY id DESC LIMIT 1) + 1;
    END IF;
END;

回答2:

I ran into a similar (yet different) requirement, where a field value in the table needed to be based on the new record's Auto Increment ID. I found two solutions that worked for me.

The first option was to use an event timer that runs every 60 seconds. The event updated the records where my field was set to the default of null. Not a bad solution if you don't mind the up to 60 second delay (you could run it every 1 second if the field that is being update is indexed). Basically the event does this:

CREATE EVENT `evt_fixerupper`
ON SCHEDULE EVERY 1 MINUTE
ENABLE
COMMENT ''  DO
BEGIN
  UPDATE table_a SET table_a.other_field=CONCAT(table_a.id,'-kittens')
  WHERE ISNULL(table_a.other_field);
END;

The other option was to generate my own unique primary IDs (rather than relying upon AUTOINCREMENT. In this case I used a function (in my application) modeled after the perl module https://metacpan.org/pod/Data::Uniqid. the generated ID's are huge in length, but they work well, and I know the value before I insert, so I can use it to generate values for additional fields.

来源：https://stackoverflow.com/questions/16597467/mysql-after-insert-trigger-get-auto-incremed-value-update-field-value-after-ins

标签

mysql

triggers