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SELECT
A.CODE,
B.NAME
FROM T_A A
LEFT JOIN T_B B
ON A.CODE = B.CODE
SELECT
A.CODE
FROM T_A A
LEFT JOIN T_B B
ON A.CODE = B.CODE
SELECT
A.CODE,
B.NAME
FROM T_A A
LEFT JOIN T_B B
ON A.CODE = B.CODE
SELECT
A.CODE,
B.NAME,
B.MEMO
FROM T_A A
LEFT JOIN T_B B
ON A.CODE = B.CODE
这两段SQL的执行时间却是几乎一样的,有点想不通