feat: support use sql to construct graph for loader

[simon824]

closed #262

[imbajin]

could u add a user case for it? (in the comment area)

[simon824]

could u add a user case for it? (in the comment area)

1. Vertices/edges and properties are not in the same table, need to join them.
2. Need to apply sql function on the specified column.

[imbajin]

could u add a user case for it? (in the comment area)

1. Vertices/edges and properties are not in the same table, need to join them.
2. Need to apply sql function on the specified column.

Thanks. Do we have a minimal sql case for it? And it's useful for user-doc later

[simon824]

Thanks. Do we have a minimal sql case for it? And it's useful for user-doc later

select t1.name, t1.age, t2.city from t1 left join t2 on t1.id = t2.id where t2.date > '2021-01-01'

I can help to update doc later.

[imbajin]

Thanks, u could add a doc later