SQL Syntax

Structured Query Language (SQL) is the standard language for managing and manipulating relational databases. It provides a powerful and flexible way to interact with data stored in database management systems (DBMS) like MySQL, PostgreSQL, Oracle, and Microsoft SQL Server. SQL syntax comprises a set of rules and conventions that dictate how you can communicate with a database.

SQL Statements

SQL commands are categorized into several types of statements, each designed for a specific purpose:

Data Query Statements

These statements retrieve data from a database:

SELECT

The SELECT statement is used to retrieve one or more rows of data from one or more tables. You can specify the columns you want to retrieve, filter results, and sort data using the ORDER BY clause.

SELECT column1, column2 FROM table WHERE condition;

Data Manipulation Statements

These statements modify data in the database:

INSERT

The INSERT statement adds new rows to a table:

INSERT INTO table (column1, column2) VALUES (value1, value2);

UPDATE

The UPDATE statement modifies existing data in a table:

UPDATE table SET column1 = value1 WHERE condition;

DELETE

The DELETE statement removes rows from a table:

DELETE FROM table WHERE condition;

Data Definition Statements

These statements define, alter, or drop database objects:

CREATE TABLE

The CREATE TABLE statement creates a new table with specified columns and data types:

CREATE TABLE table_name (
    column1 datatype,
    column2 datatype
);

ALTER TABLE

The ALTER TABLE statement modifies an existing table, such as adding or dropping columns:

ALTER TABLE table_name
ADD column_name datatype;

DROP TABLE

The DROP TABLE statement deletes an existing table and its data:

DROP TABLE table_name;

SQL Clauses

SQL statements often include one or more clauses to refine their behaviour:

WHERE Clause

The WHERE clause filters rows based on a specified condition:

SELECT column1, column2 FROM table WHERE condition;

ORDER BY Clause

The ORDER BY clause sorts the result set based on one or more columns:

SELECT column1, column2 FROM table ORDER BY column1 ASC, column2 DESC;

GROUP BY Clause

The GROUP BY clause groups rows based on specified columns, often used with aggregate functions like COUNT, SUM, or AVG:

SELECT column1, COUNT(column2) FROM table GROUP BY column1;

SQL Keywords

SQL includes a set of reserved keywords that are fundamental to constructing queries:

SELECT: Retrieves data from a table.
FROM: Specifies the source table for a query.
WHERE: Filters rows based on a condition.
INSERT INTO: Adds new rows to a table.
UPDATE: Modifies existing data in a table.
DELETE FROM: Removes rows from a table.
CREATE TABLE: Defines a new table.
ALTER TABLE: Modifies an existing table.
DROP TABLE: Deletes a table.
ORDER BY: Sorts the result set.
GROUP BY: Groups rows for aggregation.

Understanding SQL syntax is crucial for effectively working with relational databases. This overview provides a foundation for constructing SQL statements, using clauses to refine queries, and recognizing essential SQL keywords. SQL’s power lies in its ability to retrieve, manipulate, and manage data, making it a fundamental tool for anyone dealing with databases.