Client applications use Structured Query Language (SQL) statements to carry out database tasks, such as retrieving information or inserting rows into tables.
Depending how a client application is developed, SQL statements could be supplied in function calls from the programming language, or you may build them graphically in a special window provided by the application development tool.
The programming interface delivers SQL statements to the database server. The database server executes them and returns results to the application.
Client/server communication protocols carry information between the client application and the database server. Programming interfaces define how an application sends the information. No matter which interface and network protocol you use, SQL statements are sent to a server, and the results of SQL statements return to the client application.