string sql1 = "select * from (select distinct left(start_bin_value,6) from sys_mast_inter_bin_table mast join cht_card_brand cb on mast.card_brand = cb.index_field join cht_country ctry on mast.bin_country = ctry.index_field join cht_service_type st on mast.service_type = st.index_field where cb.card_brand = '" + this.Card_brand + "' and ctry.client_country = '" + this.Bin_country + "' and st.service_type = '" + this.Service_type + "' ) where rownum <= " + this.TestCases + " order by dbms_random.value";
Not a solution to your question, but another problem you have.
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[
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SQL Injection[
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SQL Injection Attacks by Example[
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PHP: SQL Injection - Manual[
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SQL Injection Prevention Cheat Sheet - OWASP[
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