SQL 服务器查询 - 哪个性能更好？

Question

我认为查询 1 比查询 2 更具可读性，但我想知道它们在性能方面是否存在差异？

查询 1

UPDATE table_1
SET col_1 = 
      CASE WHEN table_1.col_pk IS NULL THEN value1
           ELSE value2
      END
FROM table_1
LEFT JOIN table_2 ON table_1.col_pk = table_2.col_pk

或

查询 2

UPDATE table_1
SET col_1 = value1
FROM table_1
LEFT JOIN table_2 ON table_1.col_pk = table_2.col_pk
WHERE table_1.col_pk IS NULL

UPDATE table_1
SET col_1 = value2
FROM table_1
INNER JOIN table_2 ON table_1.col_pk = table_2.col_pk

Answer 1

第一个查询可能会有更好的性能，因为它只需要 table_1 和 table_2.

的单次扫描