Question

I have two tables, TABLE_1 and TABLE_2.

TABLE_1 contains ID and NAME, where ID is a primary key.

TABLE_2 contains ID and DATA, where ID and DATA form a compound primary key.

1. I’m looking for a SQL query that updates the ID in TABLE_2 when they are changed in TABLE_1.

2. How can I create this table structure?

TABLE_1

ID      NAME
100     LLL
101     KKK
102     JJJ

TABLE_2

ID      DATA
100     HHHHHHH
100     MMMMMMM
100     ZZZZZZZ
101     IIIIIII
101     FFFFFFF
102     EEEEEEE

Thank you for your help.

Answer 1

Not sure why you need to do this, but anyway.

One way to do this is to use foreign key constraints, available in the InnoDB storage engine:

CREATE TABLE `TABLE_1` (
  `ID` int NOT NULL,
  `NAME` varchar(255) NOT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB;

CREATE TABLE `TABLE_2` (
  `ID` int(11) NOT NULL,
  `DATA` varchar(255) NOT NULL,
  PRIMARY KEY (`ID`,`DATA`),
  CONSTRAINT `FK_ID` FOREIGN KEY (`ID`) 
    REFERENCES `TABLE_1` (`ID`) 
    ON UPDATE CASCADE
    ON DELETE CASCADE
) ENGINE=InnoDB;

The above table structure will update all the matching ID from TABLE_2 whenever an ID in TABLE_1 is modified (ON UPDATE CASCADE). Also, whenever you delete an ID from TABLE_1, all the matching entries from TABLE_2 will also be deleted (ON DELETE CASCADE). Because of this constraint, the ID from TABLE_2 has to exist in TABLE_1 for an INSERT to complete successfully.

Also keep in mind that foreign keys affect performance, but without knowing exactly why you want such a thing, I cannot suggest any better solution.