Keywords are words that have special meanings in SQL statements.
The statement keyword, the first keyword in an SQL statement, is usually a verb. For example, in the INSERT statement, the first keyword is INSERT.
Other keywords appear throughout a statement as qualifiers (for example, DISTINCT, PERMANENT), or as words that introduce clauses (for example, IN, AS, AND, TO, WHERE).
By convention, keywords appear entirely in uppercase letters. However, SQL keywords are not case-sensitive and can be in uppercase or lowercase letters.
For example, SQL interprets the following SELECT statements identically:
Select Salary from Employee where EmpNo = 10005; SELECT Salary FROM Employee WHERE EmpNo = 10005; select Salary FRom Employee WherE EmpNo = 10005;
All keywords must be from the ASCII repertoire. Full-width letters are not valid regardless of the character set being used.
For information on restricted keywords, see Restricted Words.