sql to determine version number is not deterministic

[robacarp]

My experience with postgres shows that a SELECT statement cannot be trusted to order the data in a consistent way, especially with older tables. While porting some unrelated migration history over to migrate.cr, I found that I needed to change the current_version sql slightly:

    def current_version
-      query = "SELECT %{column} FROM %{table}" % {
+      query = "SELECT %{column} FROM %{table} ORDER BY %{column} DESC" % {
        column: @column,
        table:  @table,
      }

      @db.scalar(query).as(Int32 | Int64)
    end

It's possible I'm misunderstanding the point of what that method does, but this tweak got it working for me.

[vladfaust]

@robacarp there is a single version value in migrate.cr's table, no need for ordering then. You may be confused with micrate's tons of rows 😊

[robacarp]

Great context, thanks.