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→SQL Coding rules
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However, we must not used alias for update request as they are not compatible with Mysql 3.1.
However, we must not used alias for update request as they are not compatible with Mysql 3.1.
−* All SELECT * are forbidden ! Any SELECT must define complete list of fields to get. This avoid confusion. Example:
+* Using SELECT * is forbidden ! When using SELECT you must define complete list of fields to get. This avoids confusion. Example:
<source lang="sql">
<source lang="sql">
SELECT field_a, field_b, field_c FROM table_1 WHERE field_d = '$id'
SELECT field_a, field_b, field_c FROM table_1 WHERE field_d = '$id'
</source>
</source>
−* Into SQL requests, you must quote fields except fields that contains amounts that must be stored as double or real type. Quotes on numbers may results in saving a different value. For example 412.62 in an insert will be saved with value 412.61999512 into database (due to implicit conversion string to numeric) if target field has type double(24,8). Only PHP see value 412.61999512. Other tools will see 412.62 giving sensation that there is no problem. But it's PHP that hase the good vision. There is really a wrong value into database. By removing quotes on numbers, no problem occurs.
+* Into SQL requests, you must quote fields except the fields that contain amounts which must be stored as double or real type. Quotes on numbers may result in saving as a different value. For example 412.62 in an insert will be saved as value 412.61999512 into database (due to implicit conversion string to numeric) if the target field has type double(24,8). Only PHP see value 412.61999512. Other tools will see 412.62 giving a sense that there is no problem. But it's PHP that has the good vision. There is really a wrong value into database. By removing quotes on numbers, no problem occurs.
Example:
Example:
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'MU' (for unit prices), 'MT' (for total prices) or 'MS' (otherwise) depending on usage of number. (see function documentation)
'MU' (for unit prices), 'MT' (for total prices) or 'MS' (otherwise) depending on usage of number. (see function documentation)
−* Functions NOW or SYSDATE are forbidden inside SQL requests. If you must use the current date into a field, value must come from the PHP and not from the database engine. This is to avoid a better portability of code and a correct management of TimeZone.
+* Functions NOW or SYSDATE are forbidden inside SQL requests. If you must use the current date into a field, value must come from the PHP and not from the database engine. This is for better portability of code and correct management of TimeZone.
== Mysql specificities ==
== Mysql specificities ==