(mysql.info.gz) SET

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 11.4.5 The `SET' Type
 ---------------------
 
 A `SET' is a string object that can have zero or more values, each of
 which must be chosen from a list of allowed values specified when the
 table is created.  `SET' column values that consist of multiple set
 members are specified with members separated by commas (`,').  A
 consequence of this is that `SET' member values cannot themselves
 contain commas.
 
 For example, a column specified as `SET('one', 'two') NOT NULL' can have
 any of these values:
 
      ''
      'one'
      'two'
      'one,two'
 
 A `SET' can have a maximum of 64 different members.
 
 Starting from MySQL 3.23.51, trailing spaces are automatically deleted
 from `SET' member values when the table is created.
 
 MySQL stores `SET' values numerically, with the low-order bit of the
 stored value corresponding to the first set member.  If you retrieve a
 `SET' value in a numeric context, the value retrieved has bits set
 corresponding to the set members that make up the column value.  For
 example, you can retrieve numeric values from a `SET' column like this:
 
      mysql> SELECT SET_COL+0 FROM TBL_NAME;
 
 If a number is stored into a `SET' column, the bits that are set in the
 binary representation of the number determine the set members in the
 column value.  For a column specified as `SET('a','b','c','d')', the
 members have the following decimal and binary values:
 
 `SET'       *Decimal       *Binary Value*
 *Member*    Value*         
 `'a''       `1'            `0001'
 `'b''       `2'            `0010'
 `'c''       `4'            `0100'
 `'d''       `8'            `1000'
 
 If you assign a value of `9' to this column, that is `1001' in binary,
 so the first and fourth `SET' value members `'a'' and `'d'' are
 selected and the resulting value is `'a,d''.
 
 For a value containing more than one `SET' element, it does not matter
 what order the elements are listed in when you insert the value.  It
 also does not matter how many times a given element is listed in the
 value.  When the value is retrieved later, each element in the value
 will appear once, with elements listed according to the order in which
 they were specified at table creation time.  If a column is specified as
 `SET('a','b','c','d')', then `'a,d'', `'d,a'', and `'d,a,a,d,d'' all
 will appear as `'a,d'' when retrieved.
 
 If you set a `SET' column to an unsupported value, the value will be
 ignored.
 
 `SET' values are sorted numerically.  `NULL' values sort before
 non-`NULL' `SET' values.
 
 Normally, you search for `SET' values using the `FIND_IN_SET()'
 function or the `LIKE' operator:
 
      mysql> SELECT * FROM TBL_NAME WHERE FIND_IN_SET('VALUE',SET_COL)>0;
      mysql> SELECT * FROM TBL_NAME WHERE SET_COL LIKE '%VALUE%';
 
 The first statement finds rows where SET_COL contains the VALUE set
 member. The second is similar, but not the same: It finds rows where
 SET_COL contains VALUE anywhere, even as a substring of another set
 member.
 
 The following statements also are legal:
 
      mysql> SELECT * FROM TBL_NAME WHERE SET_COL & 1;
      mysql> SELECT * FROM TBL_NAME WHERE SET_COL = 'VAL1,VAL2';
 
 The first of these statements looks for values containing the first set
 member.  The second looks for an exact match. Be careful with
 comparisons of the second type. Comparing set values to `'VAL1,VAL2''
 will return different results than comparing values to `'VAL2,VAL1''.
 You should specify the values in the same order they are listed in the
 column definition.
 
 If you want to determine all possible values for a `SET' column, use
 `SHOW COLUMNS FROM TBL_NAME LIKE SET_COL' and parse the `SET'
 definition in the second column of the output.
 

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