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阅读有关数字数据类型的Postgresql 文档 让我想到了这个问题：为什么在 Postgresql 中使用数据类型Float（SQL 标准）会得到这些意外的结果Numeric？

例如：

CREATE TEMP TABLE testnum (a numeric, b float);
INSERT INTO testnum VALUES (100,100);
INSERT INTO testnum VALUES (9*9*9,9*9*9);
INSERT INTO testnum VALUES (9^9^9,9^9^9);
SELECT (a/3)*3 AS numeric, (b/3) * 3 AS float FROM testnum;
SELECT (a/5)*5 AS numeric, (b/5) * 5 AS float FROM testnum;

然后运行

SELECT (a/3)*3 AS numeric, (b/3) * 3 AS float FROM testnum;

numeric                                     |         float          
                        99.9999999999999999 |                    100
                       729.0000000000000000 |                    729

在这个测试中Float …