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Unique constraints & insert or update for both MySQL and SQLite

I am looking for a way to define a set of columns as unique and then insert a new entry into the table or update the row if the columns aren't unique. I have done some research and found ways to do it, but I couldn't find anything that is compatible with both MySQL and SQLite.
Say I have the following table:
CREATE TABLE `users` (
`id` INT NOT NULL AUTO_INCREMENT,
`uuid` VARCHAR ( 64 ) NOT NULL,
`name` VARCHAR ( 32 ) NOT NULL,
`date` BIGINT NULL,
PRIMARY KEY ( id )
);
I want uuid and date to be unique so that there can be multiple entries for one uuid or one date, but not for one combination of uuid and date. What I initially wanted to do is set the primary key to those:
PRIMARY KEY ( uuid, date )
However, for some reason I won't be able to use null values for date when doing this.
I have also found something about a constraint, but I am not sure if this works:
CONSTRAINT user UNIQUE ( `uuid`, `date` )
Now I want to insert a new row into this table, but update the existing row if a row with the same uuid and date already exists. I have found a few ways but they are either not doing what I want or not compatible with both MySQL and SQLite:
INSERT INTO ... ON DUPLICATE KEY doesn't work with SQLite
REPLACE INTO will delete anything I don't specify instead of updating
I have been doing research for quite a while but I couldn't find a solution that worked for me. Any help appreciated.

SQLite solution (same principle should apply in mysql)
You could simply add a UNIQUE index (at least for SQLite for which this is for) so you could have :-
DROP TABLE IF EXISTS `users`;
CREATE TABLE IF NOT EXISTS `users` (
`id` INTEGER, //<<<<<<<<<< See notes below
`uuid` VARCHAR ( 64 ) NOT NULL,
`name` VARCHAR ( 32 ) NOT NULL,
`date` BIGINT NULL,
PRIMARY KEY ( `id` )
);
CREATE UNIQUE INDEX IF NOT EXISTS uuid_date ON `users` (`uuid`,`date`); //<<<<<<<<<<
Note AUTO_INCREMENT results in a failure for SQLite as it's not a keyword, the correct keyword in SQlite is AUTOINCREMENT. However, it's been omitted as it's probably not required as INTEGER PRIMARY KEY (or the implicit by specifiying PRIMARY KEY (id)) will result in a uniqiue id being automatically generated if no value is supplied for the column when inserting.
SQLite requires INTEGER, not INT, for the automatically generated id. NOT NULL and also UNIQUE are implied so no need to specify them.
Here's two sets of example inserts each duplicating the uuid/date combination thus updating instead of inserting and also inserting with same uuid but different date and vice-versa :-
INSERT OR REPLACE INTO `users` VALUES(null,'Fred01234567','Fred Bloggs the 1st','20180101');
INSERT OR REPLACE INTO `users` VALUES(null,'Fred01234567','Fred Bloggs the 2nd','20180101'); -- <<<< DUPLICATE
INSERT OR REPLACE INTO `users` VALUES(null,'Fred99999999','Fred Bloggs the 2nd','20180101'); -- <<<< different uuid same date
INSERT OR REPLACE INTO `users` VALUES(null,'Fred01234567','Fred Bloggs the 2nd','99999999'); -- <<<< same uuid different date
INSERT OR REPLACE INTO `users` (`uuid`,'name','date') VALUES('Fred76543210','Fred NotBloggs the 1st','20180202');
INSERT OR REPLACE INTO `users` (`uuid`,'name','date') VALUES('Fred76543210','Fred NotBloggs the 1st','20180202');
INSERT OR REPLACE INTO `users` (`uuid`,'name','date') VALUES('Fred99999999','Fred NotBloggs the 1st','20180202');
INSERT OR REPLACE INTO `users` (`uuid`,'name','date') VALUES('Fred76543210','Fred NotBloggs the 1st','99999999');
SELECT * FROM `users`;
Results are :-

I have been googling for a few hours and did some testing with both MySQL and SQLite and I think I found a working solution.
To make the combination of uuid and date unique, I have added a unique constraint to the table. To insert a new row or 'update' an existing row, I am using REPLACE INTO ... SELECT.
To create the table:
CREATE TABLE IF NOT EXISTS `users` (
`id` INT NOT NULL AUTO_INCREMENT, // use INTEGER NOT NULL for SQLite
`uuid` VARCHAR ( 64 ) NOT NULL,
`name` VARCHAR ( 32 ) NOT NULL,
`date` BIGINT NULL,
CONSTRAINT `uuid_date` UNIQUE ( `uuid`, `date` ),
PRIMARY KEY ( `id` )
);
The CONSTRAINT will make sure the combination of uuid and date is always unique.
For inserting data, I use REPLACE INTO ... SELECT, where I enter all (new) values in the SELECT query and enter the column names for all columns I haven't specified a value for, to ensure it will keep their values intact rather than deleting them when the existing row is replaced.
REPLACE INTO `users`
SELECT `id`, `uuid`, ?, `date`
FROM `users` WHERE `uuid` = ? AND `date` = ?;
Of course, because in this case there are no columns that can be lost when using a normal REPLACE INTO, so I could also use:
REPLACE INTO `users` ( `uuid`, `name`, `date` ) VALUES ( ?, ?, ? );
However, the REPLACE INTO ... SELECT query can be useful when I have a table with more columns and there are actually columns that can be lost when not selecting them.

Sorry about all the comments. Here is how I achieved what I think you are going for. You are going to lose the id as Primary Key on your users table. You will also have to stage your insert variables in a table. But you will get your end results. Sorry I do not have a better solution.
DROP TABLE users;
DROP TABLE users2;
CREATE TABLE `users` (
`uuid` VARCHAR ( 64 ) NOT NULL,
`name` VARCHAR ( 32 ) NOT NULL,
`date` BIGINT NULL
);
ALTER TABLE `users` ADD PRIMARY KEY(`uuid`,`date`);
INSERT INTO users (`name`,`uuid`,`date`) SELECT '','123','2018-04-01';
CREATE TABLE `users2` (
`uuid` VARCHAR ( 64 ) NOT NULL,
`name` VARCHAR ( 32 ) NOT NULL,
`date` BIGINT NULL
);
INSERT INTO users2 (`name`,`uuid`,`date`) SELECT 'brad','123','2018-04-01';
REPLACE INTO users SELECT `uuid`,`name`,`date` FROM users2 GROUP BY `uuid`,`date`;
SELECT * FROM users;`

Order execution of create table using mysql, h2 and flyway

I have created a an sql script (using mysqldump) to determine my base version of my database. I use this script with flywaydb to totally manage the db creation and other migration actions. The script contains of several tables some of them are fk's to others. the order in which they appear in the sql script generated by mysqldump is the following (only two of the tables appear that are causing the issue described later below)
CREATE TABLE `signaling_interface` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`test_server_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `UK_sigInterfaceConstraint` (`test_server_id`),
KEY `FK_3crdx5y8had0g1mit1k2gebt5` (`test_server_id`),
CONSTRAINT `FK_3crdx5y8had0g1mit1k2gebt5` FOREIGN KEY (`test_server_id`) REFERENCES `test_server` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `test_server` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `UK_3754w88bn333h1dgambvwj6i8` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
I want to Junit test my migrations and chose h2 in memory database to do that. But when I try to migrate it gives me an error when creating signaling_interface table because test_server does not exist. It doesn't give me this error when executing migrations in MySQL. Is there a difference between mysql and h2?

How to add an auto increment column in java?

I want to add the database from my jform and there's a column which will be auto incremented, like when i click done, the data will be inserted and a column receipt_no will have a value 1. Next time I click done then this value should be 2 and so on.
So the problem is, i have created a table with receipt_no as the primary key and auto increment, so what should be my query in java, to add the data correctly in the table.
String sql = "insert into table_name values('"++"',...)";
Can you help me in this query?

Step 1: Creating table in MySQL
CREATE TABLE `user_master` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`Firstname` varchar(45) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Step 2: Insert record
INSERT INTO user_master (`Firstname`) values('Vicky');
Step 3: Fetch record
SELECT * FROM user_master;

I can't comment so there is an answer to the comment you posted in your question:
If your table is
CREATE TABLE users(
id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
firstname VARCHAR(25) NOT NULL,
lastname VARCHAR(25) NOT NULL,
);
You can simply auto_increment the primary by not giving it on your SQL request:
INSERT INTO users(firstname, lastname) VALUES('Steve', 'Jobs');
Java don't have to generate auto increment, it is SQL job :)

Get the value of the last inserted record

I am trying to get the stop_name of the last inserted row in the table with preparedStatement. How can I get the last inserted one?
I appreciate any help.
behavoiur table:
CREATE TABLE IF NOT EXISTS behaviour(
behaviour_id INT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
mac VARCHAR(30) NOT NULL,
stop_name VARCHAR(30) NOT NULL,
stop_distance INT(11) NOT NULL,
speed INT(11) NOT NULL,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

You may try this query:
select stop_name from behaviour where created_at in (select max(created_at) from behaviour)

Another solution:
select stop_name from behaviour order by behaviour_id desc limit 1;

My Insert Into Statement is not working

I was working with UIs where the user will click the add button to add employees, but when I do it, it gives me an error like this
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`finalpayroll`.`personal_info`, CONSTRAINT `personal_info_ibfk_1`
How would I fix this?? I know I am using a parent key, and its foreign key is the User, and also take note that the parent key has already a data, but it seems my query won't work, why is that? I am using a foreign key with delete cascade and on update cascade so that when I delete a data, all of the child table rows will be deleted, vice versa. here's my key for adding or inserting statements
public void addEmployee(Personal p ,Contact c,Employee e) {
Connection conn = Jdbc.dbConn();
Statement statement = null;
String insert1 = "INSERT INTO personal_info (`First_Name`, `Middle_Initial`, `Last_Name`, `Date_Of_Birth`, `Marital_Status`, `Beneficiaries`) VALUES ('"+p.getFirstName()+"', '"+p.getMiddleInitial()+"'" +
" , '"+p.getLastName()+"', '"+p.getDateOfBirth()+"', '"+p.getMaritalStatus()+"', '"+p.getBeneficiaries()+"')";
try {
statement = conn.createStatement();
statement.executeUpdate(insert1);
statement.close();
conn.close();
JOptionPane.showMessageDialog(null, "Employee Added!!");
} catch(Exception ex) {
ex.printStackTrace();
}
}
Users table:
CREATE TABLE `users` (
`idusers` int(11) NOT NULL AUTO_INCREMENT,
`emp_id` varchar(45) DEFAULT NULL,
`emp_pass` varchar(45) DEFAULT NULL,
PRIMARY KEY (`idusers`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1
Personal_info table:
CREATE TABLE `personal_info` (
`idpersonal_info` int(11) NOT NULL AUTO_INCREMENT,
`First_Name` varchar(45) DEFAULT NULL,
`Middle_Initial` varchar(45) DEFAULT NULL,
`Last_Name` varchar(45) DEFAULT NULL,
`Date_Of_Birth` varchar(45) DEFAULT NULL,
`Marital_Status` varchar(45) DEFAULT NULL,
`Beneficiaries` varchar(45) DEFAULT NULL,
PRIMARY KEY (`idpersonal_info`),
CONSTRAINT `personal_info_ibfk_1`
FOREIGN KEY (`idpersonal_info`)
REFERENCES `users` (`idusers`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1

You are trying to insert a record with 6 fields: First_Name, Middle_Initial, Last_Name, Date_Of_Birth, Marital_Status and Beneficiaries. Your schema is currently unknown but none of these fields seem to be a candidate foreign key to id of User table you mentioned. Thus I think there is a default value for that foreign key column and that default value is missing in User table.
Needless to say, you shouldn't have a default value for a foreign key of any table..
I am adding these information regarding your questions in comments and update on your question:
A foreign key is a link between a child table and parent table, personal_info and users tables in your case respectively. Child table's foreign key column must reference to a key value in parent table which means that for every value in child table's FK column, there must be a value in parent table's linked column.
Now, in your case when you try to insert a new personal_info record MySQL assigns a idpersonal_info to it, since you defined it as auto increment. But since there is a link to users table, MySQL searchs for the new idpersonal_info to be inserted in users table's idusers column. And as you are getting this exception, you surely don't have that value in the users table.
You can change your table structure as follows:
CREATE TABLE `personal_info` (
`idpersonal_info` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) NOT NULL,
... OTHER FIELD DEFINITIONS,
PRIMARY KEY (`idpersonal_info`),
CONSTRAINT `user_id_fk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`idusers`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB
And your query will need to include user_id field as well. So it will be something like this:
INSERT INTO personal_info
(`user_id`, `First_Name`, `Middle_Initial`, `Last_Name`, `Date_Of_Birth`, `Marital_Status`, `Beneficiaries`)
VALUES ( .... SET YOUR VALUES HERE. DON'T FORGET TO SET A VALID USER_ID

Looks like in your Personal_Info table you have a column called "finalpayroll", that points to a column in another table (a foreign key) and it's required (not nullable). In your insert you're not giving it a value. So what you could do is make that column nullable.
Or could be the other way around as #Konstantin Naryshkin is saying

What the error means is that you are trying to insert a value into a column with a foreign key a value that is not in the remote table.
I assume that there is a user column that we are not seeing. Since you are not explicitly setting the value, I assume that it is getting a default. The default value is not in the parent table.