fix: Allow column reference in default expressions for MySQL and MariaDB

[joc-a]

MySQL and MariaDB are the only supported databases that allow referencing another column in a default expression, but for this to work, the referenced column must be one that occurs earlier in the table definition. This was not working because Exposed was sorting the columns by column name for the insert statement. Not sorting fixes this issue.

[obabichevjb]

It looks good to me,

The only reason to make sorting I see is stable DDL generation. Sorting allows to get all the columns in the same order independently from how it was added to the table object.

I expect that if somebody already has generated tables, may get diff in DDL after that change. If you write a test that check that there is no change in ddl between two identical tables but with different columns order (if it is really so) it would be nice.

[joc-a]

It looks good to me,

The only reason to make sorting I see is stable DDL generation. Sorting allows to get all the columns in the same order independently from how it was added to the table object.

I expect that if somebody already has generated tables, may get diff in DDL after that change. If you write a test that check that there is no change in ddl between two identical tables but with different columns order (if it is really so) it would be nice.

@Test
fun testSameTableWithDifferentColumnOrder() {
    val tester1 = object : Table("tester") {
        val aColumn = integer("aColumn")
        val bColumn = integer("bColumn")
        val cColumn = integer("cColumn")
    }
    val tester2 = object : Table("tester") {
        val cColumn = integer("cColumn")
        val bColumn = integer("bColumn")
        val aColumn = integer("aColumn")
    }
    withDb {
        assertEquals(tester1.ddl, tester2.ddl)
    }
}

This would fail even before the changes in this PR, but it's not clear to me why we would ever need identical DDL for two identical tables with different column order. Could you please clarify?

[obabichevjb]

But this one does not fail now:

@Test
fun testSameTableWithDifferentColumnOrder() {
    val tester1 = object : Table("tester") {
        val aColumn = integer("aColumn")
        val bColumn = integer("bColumn")
        val cColumn = integer("cColumn")
    }
    val tester2 = object : Table("tester") {
        val cColumn = integer("cColumn")
        val bColumn = integer("bColumn")
        val aColumn = integer("aColumn")
    }
    withTables(tester1) {
        assertEqualLists(emptyList(),  SchemaUtils.statementsRequiredToActualizeScheme(tester2))
    }
}

I checked, in your branch it does not fail also, so it 's not a breaking change finally. I should check it earlier)

[joc-a]

@obabichevjb Oh, I see what you mean. Yeah, that's because detecting the difference between the Exposed table and the table in the database does not depend on the order of the columns. Thank you for the extra check!