I literally always have to look up the meaning of :limit in migrations when it comes to integer values. Here's an overview. Now let's memorise it (oh, this works for MySQL, other databases may work differently):

:limit Numeric Type Column Size Max value
1 tinyint 1 byte 127
2 smallint 2 bytes 32767
3 mediumint 3 byte 8388607
nil, 4, 11 int(11) 4 byte 2147483647
5..8 bigint 8 byte 9223372036854775807

Note: by default MySQL uses signed integers and Rails has no way (that I know of) to change this behaviour. Subsequently, the max. values noted are for signed integers.

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