Kawash, Jalal (2004) Complex quantification in Structured Query Language (SQL): a tutorial using relational calculus - Journal of Computers in Mathematics and Science Teaching ISSN 0731-9258 Volume 23, Issue 2, 2004 AACE Norfolk, Virginia. Retrieved from Thefreelibrary.com (页面存档备份,存于互联网档案馆).
Kawash, Jalal (2004) Complex quantification in Structured Query Language (SQL): a tutorial using relational calculus - Journal of Computers in Mathematics and Science Teaching ISSN 0731-9258 Volume 23, Issue 2, 2004 AACE Norfolk, Virginia. Retrieved from Thefreelibrary.com (页面存档备份,存于互联网档案馆).