A point of optimizing SQL query statements

Optimization | statement
(1) INSERT [into] b SELECT ID, field1, field2 from A WHERE does EXISTS (select id from b where id=[a.] Id

(2) INSERT [into] B SELECT * from A WHERE-id not in (SELECT ID from B)

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These two sentences are inserted into table B and the association comparison field ID by inserting data that exists in table A but does not exist in table B.
But the execution efficiency of these two sentences is different in order of magnitude.

The conclusion has two points:
Try to use EXISTS and not EXISTS instead of in and not to be lazy, try not to select * from ..., but to write segment name Select Field1,field2,....