问题
I know that I should use it when I deal with data of TEXT type (and I guess the ones that fall back to TEXT), but is it the only case?
Example:
UPDATE names SET name='Mike' WHERE id=3
I'm writing an SQL query auto generation in C++, so I want to make sure I don't miss cases, when I have to add quotes.
回答1:
Single quotes (') denote textual data, as you noted (e.g., 'Mike' in your example). Numeric data (e.g., 3 in your example), object (table, column, etc) names and syntactic elements (e.g., update, set, where) should not be wrapped in quotes.
回答2:
The single quote is the delimiter for the string. It lets the parser know where the string starts and where it ends as well as that is is a string. You will find that sometimes you get away with a double quote too.
The only way to be certain you don't miss any cases would be to escape the input, otherwise this will be vulnerable to abuse when somehow a single quote ends up in in the text.
来源：https://stackoverflow.com/questions/32926814/when-to-use-single-quotes-in-an-sql-statement