SQL Macro Part2 column_value = nvl(:param, column_value)

Hi,

Since I am working on “SQL Macro”, I am keep testing things. so please see my previous post: http://mustafakalayci.me/2020/10/28/sql-macro-is-finally-here/

as mentioned in previous post, is it possible to get rid of column_value = nvl(:param, column_value) conditions? since they become a huge pain in big and complex queries. I provided a very cumbersome solution in previous post., I wanted to test and do more about it.

As I said I wasn’t able to read any parameter value in sql macro except numbers. So today I tried COLLECTIONS (Array) and got different results. Let’s start with COLUMNS. we can send a column list using DBMS_TF package:

so we are able to group any table based on a column and get count of it. since P_Columns is an array, we can send more columns in it but how can we use them dynamically in sql macro?

great we can use plsql to generate column list and use it in sql statement but of course this could be a little bit dangerous because we started to use “string concatenation”. Not much but a little bit because columns in DBMS_TF.COLUMS_T array must be actual columns of the previous parameter or you got an error.

since we can use collections and data is passed to plsql (unlike varchar2 parameter) may be we can use user defined collections to pass a parameter and we can! that is really excited me at first(not then).

So since I wanted to eliminate unnecessary conditions like ” column1 = nvl(:param1, column1″ if :param1 is null, I planned to pass those column name and parameter value and check them in sql macro. if parameter value is not null then add it to sql condition.

here is VERY basic version:

Viola! if I send null as the value of employee_id, just “select * from hr.employees” statement is run and a full table scan is done but when I send 100 as employee_id value “where employee_id = 100” condition is added.

PS: I am aware that my conditions are just an equality conditions and no AND/OR operator selection or grouping conditions (parenthesises for related OR  conditions) etc etc etc. this is just an example after all. I will write a proper version of it when I decided to use it.

as you can see, I send 90 as department_id value and it is in my conditions but value of salary is null and it is not in my conditions. so did we get rid of those conditions? well not exactly.

event if it seems working (and it is working) I did not used any “bind variable” in my examples. those parameters are constant values and so the query. this is the actual running code for my last example:

select “EMPLOYEE_ID”,”DEPARTMENT_ID”,”FIRST_NAME”,”SALARY” from p where EMPLOYEE_ID = 100 and DEPARTMENT_ID = 90

so no bind variables. Let’s use one:

unfortunately, when I used bind variable I got an error from line 10 of my Sf_Generate_Sql sql macro and line 10 is where the P_Where collection is read. so somehow SQL does not initiate this collection when I used bind variable and/or it is not passed to sql macro. Even if I tried the plsql version, it is not working:

so I can not use it right now. since this is a 20c feature may be we should wait for 20c for more details and more options.

Edit:

I also wanted to add one more example, Let’s get only specified type of columns from any table:

I defined 1 as number, 2 as varchar2 etc etc. so I can get only NUMBER columns from a table (any table actually) or only varchar2 columns.

SQL Macro has a great functionality improvement for SQL in my opinion. since 20c is not accessible yet I can not try SCALAR sql macro but I am confident that it will save us to write many same sql fragments for many different sql statements.

wish you healthy days.

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