When people engage in simple but nontrivial actions, they usually have error rates of about 1% to 5%. When they engage in more complex cognitive activities, error rates are higher, sometimes much higher. SQL queries are a good example of this. SQL queries have a number of parameters and can incorporate Boolean operations.
Although e+xperiments used college and sometimes high school student, the Chan, Lu, & Wei  survey showed that most professional SQL users do not get a query right the first time they try.
More complex cognitive actions may represent a chain of simpler cognitive actions with lower error rates. The probabability of an error increases as the cognitive action chain length increases because probabilities multiply.
Smelcer (1995) only looked at a particular type of error. However, he measured error rates based on cognitive load. For low memory load, the error rate was only 6%. This tripled under high memory load.
|Chan, Lu, & Wei ||Percentage of 136 surveyed professional SQL users who say they usually take more than one try to do a query.||82%|
|Gould||Cited in Reisner, 1981. Query specification errors in QBW, 39 high school and college students. Per query.||33%|
|Greenblatt & Waxman ||Query specification errors, paper and pencil exercise. Per query.||25% - 27%|
|Reisner ||Query specification errors on final exam, SEQUEL, programmers. Per query.||22%|
|Smelcer ||20 undergraduates with 80 minutes of training in SQL. Only counted errors in which a required join was not used. Percentage of queries with such errors. 6% if low memory load, 12% if medium memory load, 17% with high memory load. Per query.||14%|
Chan, H. C., Lu, H. J., & Wei, K. K. (1993). A Survey of SQL Language. Journal of Database Management, 4(4), 4-15.
Reisner, P. (1981). "Human Factors Studies of Database Query Languages: A Survey and Assessment." Computing Survey, 14(1), March, pp. 13-31.
Smelcer, J. B. (1995). User Errors in Database Query Composition. International Journal of Human-Computer Studies, 42(4), 353-381.
Reisner, P., Boyce, R. F., & Chamberlin, D. D. (1975). Human Factors Evaluation of Two Data Base Query Languages--SQUARE and SEQUEL. Proceedings of the National Computer Conference, May 19-22, Arlington, Virginia, pp. 447-452