[6.x] Postgresql column precision declaration fix

[chmv]

Hello!

Briefly:
Allows you to create columns without optional precision:
"column1" timestamp WITHOUT TIME zone NOT NULL,

In detail:

Now there is no way to create Date/Time column with undefined precision as described in 8.5.1:
https://www.postgresql.org/docs/11/datatype-datetime.html#DATATYPE-DATETIME-INPUT

type [ (p) ] 'value'
where p is an optional precision specification giving the number of fractional digits in the seconds field. Precision can be specified for time, timestamp, and interval types, and can range from 0 to 6. If no precision is specified in a constant specification, it defaults to the precision of the literal value (but not more than 6 digits).

For example this code:

        Schema::create('test', function (Blueprint $table) {
            $table->timestamp('column1');
            $table->timestampsTz('column2');
            $table->time('column3');
            $table->timeTz('column4');
        });

will create this sql request:

CREATE TABLE "test"
(
    "column1" timestamp(0) WITHOUT TIME zone NOT NULL,
    "column2" timestamp(0) WITH TIME zone NOT NULL,
    "column3" time(0) WITHOUT TIME zone NOT NULL,
    "column4" time(0) WITH TIME zone NOT NULL
)

There is no way to get rid of (0) in a SQL query. Because of 0 as a default value:
public function timestamp($column, $precision = 0)

In this patch, null precision can be specified.

        Schema::create('test2', function (Blueprint $table) {
            $table->timestamp('column1', null);
            $table->timestampTz('column2', null);
            $table->time('column3', null);
            $table->timeTz('column4', null);
        });

in result:

CREATE TABLE "test2"
(
    "column1" timestamp WITHOUT TIME zone NOT NULL,
    "column2" timestamp WITH TIME zone NOT NULL,
    "column3" time WITHOUT TIME zone NOT NULL,
    "column4" time WITH TIME zone NOT NULL
)

Full backward compatibility. Since the previous behavior generated an invalid SQL query in this case.

Thank you!

P.S. This is my first pull request. Please correct me if I made a mistake. Thanks.

[driesvints]

@chmv heya. Thanks for your first pr. Can you maybe also add some tests for these changes?

[driesvints]

@staudenmeir any chance you can have a look at this? Thanks!

[chmv]

@chmv heya. Thanks for your first pr. Can you maybe also add some tests for these changes?

I'll try. How to send changes in the right way? Do I need to make a new pr or is there a way to add to this? Thank you!

[driesvints]

@chmv you can push commits onto your branch and they'll be added to this pr.

[chmv]

@driesvints Thanks! Done.

[staudenmeir]

Looks good to me.

I think it would be easier to read if we switch the two sides:

(isset($column->precision) ? "($column->precision)" : '')

[chmv]

I'm not sure if this is rightly. Of course, it's really more beautiful. My first variant was (! is_null ...), but it's ugly, so I switched it. But isset... There is an unexpected default value of 0... in other method... It might confuse someone...
Do I need to make changes to this pr?