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Before you start part 2 of this tutorial you need to ensure you have satisfy all the pre-requisites:. We used Perl 5. ODBC modules which is currently 5. Use perl --version to see what version of Perl you have installed. We used DBI 1. To see if you have a recent enough version of DBI installed run: If you get an error like "DBI version 1.
You can use similar methods as above to determine if DBD:: ODBC is installed and to see what version you have:. If you have not got DBD:: To show all drivers DBI knows about and their versions:.
We used unixODBC 2. You can find out the unixODBC version you are using with:. This tutorial assumes you have read or understand all the concepts in the previous tutorial DBD:: However, all the Perl examples should work equally well on Windows so long as minor alterations for the command line are made.
We have assumed you are using the unixODBC driver manager. You specify the data you want to retrieve from the database using SQL select statements.
The basic form of a SQL select statement we use here is:. Most databases would require the second ' to be doubled up. You can use the DBI quote method to do this for you with:. The other way recommended is to use bound parameters see Using parameters.
ODBC can describe the result-set for you listing the number of columns and the names of the columns. Some database will always uppercase column names in create statements if they are unquoted and some databases retain the case of column names if they are enclosed in the identifier quote character.
Some drivers may be unable to return a column name at all e. You can get around this using column aliases as in "select 1 as col1 from table". Similarly, the TYPE attribute returns an array reference of column types. For the 'fred' table above:. The column types are defined by international standards see the DBI manual. Here the SQL contains a parameter marker the '? When the execute method is called we pass the parameters required. You can use multiple parameter markers e.
Note You must pass the array of parameters in the order which you want them to match the parameter markers in the SQL. Note You cannot use parameter markers in place of column names e. When passing the parameters to the execute method a default binding type is used. ODBC attempts to find out what the parameter markers represent and bind the parameters as the same type. You can also bind the parameters yourself before the execute call and in this way you can specify how the parameters should be bound:.
Note Once the parameters are bound you cannot change the type they are bound as although you can obviously change the bound values. In ODBC there is usually no need to specify the type. DBI supports a number of methods returning the result-set or part of it in hash or array references. All the following examples assume you have already prepared and executed a select on a table containing two rows of two columns named a and b which look like:.
The rather elegant way of doing this in the DBI documentation is:. Databases store char n columns as exactly n characters so if you have a char 10 column which you insert 'FRED' into when you retrieve it you will get 'FRED '.
With the following table definition and inserts:. The ChopBlanks attribute is provided to help you here. ChopBlanks may be set on the connection or statement handle and is inherited from connections. The default is for ChopBlanks to be false. Other databases have memo, blob etc. You can find the current settings with:.
When LongTruncOk is false as above , if you attempt to retrieve more than LongReadLen bytes from a column you will get an error like above.
If you are not bothered about the column data being truncated then set LongTrunkOk to 1. If you need more than 80 bytes from the column then you need to set LongReadLen. If you want long columns ignored i. Columns which have the NULL value are special.
NULL is not the same as an empty string. You need to be careful using comparisons on columns which are nullable. The last state, is the one that needs a closer look. So in the query for all rows where col2 is not equal to 'Y' the rows containing a NULL are not returned, as the answer to the question "Does the col2 column contain values not equal to Y" returns false, as the column contains the unknown NULL and not a value that could or could not be equal to 'Y'.
As a result, the following Perl run against the table above:. You can use either of the following examples to avoid this:. As shown above a standard way of selecting a column which is NULL is "where column is null" but you cannot parameterise this.
This has been the subject of much discussion and one method put forward is:. Other trademarks and registered trademarks appearing on easysoft.