MySql获取数值类型的最大值的另类方法

中有的时候需要获取整数的最大值——比如在LIMIT的时候:

-- 需要获取第5条记录到最后的所有记录
-- 不得不在最后输入一个最大值,这个值如果简单点我们希望是BIGINT的最大值
-- 不过,我们忘了BIGINT的最大值是?
SELECT * FROM table_name WHERE condition=cvalue LIMIT 5, 838882;

当忘掉的最大值的时候,我们最简单的方法是使用~0,让后通过位移来取得各个整数类型的对应

-- 通过~0来获取BIGINT的最大值(无符号)
-- 通过~0的右移位数来获取各个整数类型的最大值
-- \G 是让每一列占据一行显示
SELECT ~0 as max_bigint_unsigned
,      ~0 >> 32 as max_int_unsigned
,      ~0 >> 40 as max_mediumint_unsigned
,      ~0 >> 48 as max_smallint_unsigned
,      ~0 >> 56 as max_tinyint_unsigned
,      ~0 >> 1  as max_bigint_signed
,      ~0 >> 33 as max_int_signed
,      ~0 >> 41 as max_mediumint_signed
,      ~0 >> 49 as max_smallint_signed
,      ~0 >> 57 as max_tinyint_signed
,      'This code came from internet resource -- MitchellChu' as extinfo
\G

*************************** 1. row ***************************
   max_bigint_unsigned: 18446744073709551615
      max_int_unsigned: 4294967295
max_mediumint_unsigned: 16777215
 max_smallint_unsigned: 65535
  max_tinyint_unsigned: 255
     max_bigint_signed: 9223372036854775807
        max_int_signed: 2147483647
  max_mediumint_signed: 8388607
   max_smallint_signed: 32767
    max_tinyint_signed: 127
               extinfo: This code came from internet resource -- MitchellChu
1 row in set (0.00 sec)

 看完代码是不是有恍然大悟的感觉呢?

Wednesday, October 16, 2013 | 其他技术 编程语言

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