Intermediate SQL: Understanding SQL's Order of Execution and Debugging Errors

Key Takeaways

fantastic work on using count and distinct now that we flexed our SQL muscle a bit we'll take a small step back and better understand how SQL code works unlike many programming languages SQL code is not processed in the order it is written consider we want to grab a coat from a closet first we need to know which closet contains the Coates this is similar to the from statement which is the first line to be processed before any data can be selected the table from which the data will be selected needs to be indicated next our selection is made finally the results are refined here we use the limit keyword that limits the result to a specified number of Records in this case we only want to return the first 10 names from the people table knowing processing order is especially useful when debugging and aliasing Fields and tables suppose we need to refer to an alias later on in our code in that case that Alias will only make sense to a processor when its declaration in the select statement is processed before the Alias reference is made elsewhere in the query before you begin working with more advanced queries is useful to know more about debugging SQL code and how to read the error messages some messages are extremely helpful pinpointing and even suggesting a solution for the error as this message does when we misspell the name field we'd like to select other common errors may involve incorrect capitalization or punctuation other error messages are less helpful and require us to review our code more closely forgetting a comma is a very common error let's say we've drafted this code to find all titles country of origin and duration of films the error message will alert us to the general location of the era using a carrot below the line of code which in this case points to the country field name we must examine the code a little further though to discover the missing comma is between country and duration SQL displays a similar error message when a keyword is misspelled but this time the carrot indicator below the offending line is spoton there are a few more SQL errors out there but the three mentioned in this lesson will be the most common ones we will encounter debugging is a major skill and the best way to master this skill is to make mistakes and learn from them [Music]