SQL Syntax

What is SQL Syntax?.

SQL is a declarative language that looks like natural English. At its core, an SQL statement begins with a verb describing the action, such as SELECT, INSERT, UPDATE, or DELETE, followed by the subject and predicate. This structure ensures that SQL commands read like everyday sentences.

Example:

SELECT
    product_name, price
FROM
    products
WHERE
    price < 50;

Here, we query product names and prices for items costing less than $50. The SELECT, FROM, and WHERE are SQL clauses, with some being mandatory (SELECT and FROM) and others optional (WHERE).

Understanding SQL Syntax

SQL's user-friendliness stems from its simplicity. Because SQL was designed specifically for the non-technical people. Unlike imperative languages like PHP or Java, SQL focuses on "what" you want instead of "how" you want it. This simplicity makes SQL accessible to all, from data analysts to developers and database administrators.

SQL Commands

SELECT
    emp_name, emp_id
FROM
    employees;

DELETE FROM employees
WHERE
     emp_id = 'E001';

SQL comprises a plethora of commands, each terminated with a semicolon (;). For instance, you can have two different SQL commands in a single script, separated by a semicolon:

The semicolon marks the end of a command, and each command consists of keywords, literals, identifiers, or expressions. Tokens are separated by spaces, tabs, or newlines.

Literals

SQL offers three types of literals:

• String
• Numeric
• Binary

String literals are alphanumeric characters enclosed in single quotes, e.g., 'Mark','100' ,'1996-08-15'. Numeric literals can be integers, decimals, or scientific notations, such as 200 or 6.0221415E23. SQL represents binary values as x'0000', with each digit being a hexadecimal value.

Keywords

SQL boasts numerous keywords with special meanings, like SELECT, INSERT, UPDATE, DELETE, and DROP. These keywords are reserved, meaning they can't be used as table, column, index, or view names.

1. ADD
2. ADD CONSTRAINT
3. ALL
4. ALTER
5. ALTER COLUMN
6. ALTER TABLE
7. AND
8. ANY
9. AS
10. ASC
11. BACKUP DATABASE
12. BETWEEN
13. CASE
14. CHECK
15. COLUMN
16. CONSTRAINT
17. CREATE
18. CREATE DATABASE
19. CREATE INDEX
20. CREATE OR REPLACE VIEW
21. CREATE TABLE
22. CREATE PROCEDURE
23. CREATE UNIQUE INDEX
24. CREATE VIEW
25. DATABASE
26. DEFAULT
27. DELETE
28. DESC
29. DISTINCT
30. DROP
31. DROP CONSTRAINT
32. DROP DATABASE
33. DROP DEFAULT
34. DROP INDEX
35. DROP TABLE
36. DROP VIEW
37. EXEC
38. EXISTS
39. FOREIGN KEY
40. FROM
41. FULL OUTER JOIN
42. GROUP BY
43. HAVING
44. IN
45. INDEX
46. INNER JOIN
47. INSERT INTO
48. INSERT INTO
49. IS NULL
50. IS NOT NULL
51. JOIN
52. LEFT JOIN
53. LIKE
54. LIMIT
55. NOT
56. NOT NULL
57. OR
58. ORDER BY
59. OUTER JOIN
60. PRIMARY KEY
61. PROCEDURE
62. RIGHT JOIN
63. ROWNUM
64. SELECT
65. SELECT DISTINCT
66. SELECT INTO
67. SELECT TOP
68. SET
69. TABLE
70. TOP
71. TRUNCATE TABLE
72. UNION
73. UNION ALL
74. UNIQUE
75. UPDATE
76. VALUES
77. VIEW
78. WHERE

Comments

To document SQL statements, use comments. Database engines ignore characters in comments. Single-line comments start with --, while multiline comments use /* */.

SELECT
    student_id, name
FROM
    student
WHERE
    marks < 30; -- Students with low marks