TB1_1
TB1_2
下列执行结果分别为:
SELECT COUNT(COL_1) FROM TB1_1
SELECT COUNT(DISTINCT COL_1) FROM TB1_1
SELECT AVG(COL_1) FROM TB1_1
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SELECT COL_1 FROM TB1_1 WHERE COL_1 NOT IN(SELECT COL_1 FROM TB1_2)
SELECT COL_1 FROM TB1_1 WHERE NOT EXISTS(SELECT 0 FROM TB1_2 WHERE TB1_1.COL_1=TB1_2.COL_1)