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Cheat sheet · Class 12 · CBSE · Science Computer Science

Structured Query Language (SQL) cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 12 · Computer Science

Cheat sheet

Chapter 10Structured Query Language (SQL)

Query order: SELECT … FROM … WHERE … GROUP BY … HAVING … ORDER BY.

1. Command Types

TypeCommands
DDLCREATE, ALTER, DROP
DMLINSERT, UPDATE, DELETE, SELECT

Constraints: PRIMARY KEY, FOREIGN KEY, NOT NULL, UNIQUE, DEFAULT.

2. SELECT Clauses

  • WHERE with =, <>, BETWEEN, IN, LIKE ('A%', '_b%'), IS NULL.
  • ORDER BY col ASC/DESC.
  • DISTINCT removes duplicates.
  • Aliases with AS.

3. Functions

  • Aggregate: COUNT, SUM, AVG, MAX, MIN.
  • String: UPPER, LOWER, LENGTH, SUBSTR, TRIM, INSTR.
  • Math: ROUND, POWER, MOD.
  • Date: NOW, DATE, MONTH, YEAR, DAYNAME.

4. Grouping & Joins

  • GROUP BY groups rows; HAVING filters groups (WHERE filters rows).
  • Cartesian product: every row × every row.
  • Equi-join: match on a common column; natural join removes the duplicate column.

SELECT dept, AVG(salary) FROM emp GROUP BY dept HAVING AVG(salary) > 50000;

5. Python + MySQL

  • mysql.connector.connect(host, user, passwd, database).
  • cursor.execute(query); fetchone(), fetchall().
  • commit() after INSERT/UPDATE/DELETE.

6. Key Points

  • COUNT(*) counts NULL rows; COUNT(col) doesn't.
  • DROP removes the table; DELETE removes rows.
  • % matches any length; _ one character.
  • Use parameterised queries.

Remember: DDL vs DML | WHERE vs HAVING | aggregates | joins

Structured Query Language (SQL): questions and notes

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