Aggregate Function Data Type,
SUM() AVG() Return Type Real/Float. So it is unprecise number.
另外, teradata会自动先把NULL删除后再对剩下的数据集合进行AVG(a), MAX(a), MIN(a), SUM(a), COUNT(a)。
如下例:
DROP TABLE guanwang_test_avg;
CREATE TABLE guanwang_test_avg
( a INTEGER)
;
INSERT INTO guanwang_test_avg VALUES(1);
INSERT INTO guanwang_test_avg VALUES(0);
INSERT INTO guanwang_test_avg VALUES(NULL);
SEL AVG(a), MAX(a), MIN(a), SUM(a), COUNT(a) FROM guanwang_test_avg;
Average(a) Maximum(a) Minimum(a) Sum(a) Count(a)
0.50 1 0 1 2
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