SpirirHost Support Centre: MySQL Reference Manual p.404

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

404 MySQL Technical Reference for Version 4.0.3 d 8 1000 If you assign a value of 9 to this column, that is 1001 in binary, so the rst 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 ele- ments 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 speci- ed at table creation time. For example, if a column is specied as SET("a","b","c","d"), then "a,d", "d,a", and "d,a,a,d,d" will all 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 perform a SELECT on a SET column using the LIKE operator or the FIND_IN_ SET() function: mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%'; mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0; But the following will also work: mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2'; mysql> SELECT * FROM tbl_name WHERE set_col & 1; The rst of these statements looks for an exact match. The second looks for values con- taining the rst set member. If you want to get all possible values for a SET column, you should use: SHOW COLUMNS FROM table_name LIKE set_column_name and parse the SET denition in the second column. 6.2.4 Choosing the Right Type for a Column For the most ecient use of storage, try to use the most precise type in all cases. For example, if an integer column will be used for values in the range between 1 and 99999, MEDIUMINT UNSIGNED is the best type. Accurate representation of monetary values is a common problem. In MySQL, you should use the DECIMAL type. This is stored as a string, so no loss of accuracy should occur. If accuracy is not too important, the DOUBLE type may also be good enough. For high precision, you can always convert to a xed-point type stored in a BIGINT. This allows you to do all calculations with integers and convert results back to oating-point values only when necessary. 6.2.5 Using Column Types from Other Database Engines To make it easier to use code written for SQL implementations from other vendors, MySQL maps column types as shown in the following table. These mappings make it easier to move table denitions from other database engines to MySQL: Other vendor type MySQL type BINARY(NUM) CHAR(NUM) BINARY

MySQL Reference Manual

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