@RamyaSriG1066

One of the obvious reason is that if you create a connect sql rule for your custom query then you will be using activity to call them which is not recommended unless it is last option.

Also most of the places you can directly call Report Definition rule to source for example - to source a table, dropdown, etc.

Report definition generates OOTB sql query behind the scene. This RD rule has many restrictions to take care of the performance of the query which are not present while creating an SQL query via connect sql rule.

@RamyaSriG1066

As you know pega is low-code platform and no need to have more coding knowledge to implement the process inside pega..

SQL will be used to fetch data from DB based on query which we are using.. If we need to use SQL, then we need to learn all SQL code from scratch, learning SQL would be complex comparing with pega Report-Definition.

In pega instead of writing code in SQL, you will be doing the configuration in Report-Definition based on Report-Definition configuration automatically in back-end pega will generate SQL query and will fetch data from DB.

Please refer below mentioned articles to get brief idea about Report-Definition.

Report Definition in Pega - Class Joins & Associations - OneStopPega

Sub-reports - its Configuration, Usage & Execution - OneStopPega