SHOW CREATE TABLE returns incorrect statement for json field default

[dphil]

Using dolt 0.40.21 and using a db initialized with the new DOLT_DEFAULT_BIN_FORMAT=DOLT_1 flag.

In the CREATE TABLE call, a particular column is defined as follows:
metadata json default '{}'

But if I call SHOW CREATE TABLE tablename, it shows the field as:
metadata json DEFAULT '{map[]}'

If I then try to create a new table using the output of that SHOW CREATE TABLE command, I get the following error on that field:
Error 1105: incompatible type for default value
presumably because the default should be '{}', not '{map[]}'.

[fulghum]

Thanks for reporting this one. I was able to reproduce this and will get started on the fix.

[fulghum]

Tested this with Dolt, MySQL, and read through the relevant MySQL docs a bit...

On MySQL, create table t(metadata json default '{}'); returns an error, because json/blob/text/geometry columns are not allowed to have literal default values. However, you can wrap them in parens to make them an expression default value: create table t(metadata json default ('{}'));. This works on MySQL and on Dolt. I've also confirmed the output of show create table t is the same between MySQL and Dolt when using the empty json map value as an expression.

I'll update Dolt to match MySQL's behavior here and return an error when specifying a literal column default value for json/blob/text/geometry columns.