Beginner Notes - Page 7

What NULL Really Means

NULL is not zero, not an empty string and not equal to itself. Learn what it represents, how it spreads through expressions and how to handle it delib...

SQL

SQL Numeric Functions

Rounding, truncating, absolute values, modulo and integer division - and the rounding rules that decide whether your invoice totals balance.

SQL

SQL String Functions

Concatenating, trimming, slicing, replacing and searching text - and which of these functions changes name in every dialect.

SQL

IN, BETWEEN, LIKE and IS NULL

The four filtering shortcuts you will use constantly: set membership, ranges, pattern matching with wildcards, and the only correct way to test for NU...

HTML

The img Element: Putting Pictures on a Page

src, alt, width and height. Four attributes, and three of them are doing more work than most people realise.

SQL

AND, OR, NOT and Operator Precedence

Combining conditions correctly. Precedence between AND and OR, what NOT does to a NULL, and how to keep complex filters readable and index friendly.

SQL

WHERE and Comparison Operators

WHERE decides which rows survive. Learn the comparison operators, how conditions are evaluated per row, and why a function around a column kills an in...

SQL

ORDER BY, LIMIT and Pagination

Sorting on one or many columns, NULL placement, and the four dialect specific ways to fetch page two of a result set - including why OFFSET gets slow.

SQL

Expressions, Calculated Columns and DISTINCT

Compute values in the select list, build derived columns from existing ones, and use DISTINCT correctly - including what it does across several column...

HTML

Absolute, Relative and Root Relative URLs

The same page, three ways to point at it. Learn how a browser resolves each form, when a leading slash saves you, and why one broken dot breaks an ent...

SQL

SELECT Basics: Columns, SELECT * and Aliases

The statement you will write more than all the others combined. Choose columns, alias them, and learn why SELECT * belongs in the console and not in c...

HTML

The Anchor Element: Turning Text Into a Link

One element built the web. Learn the href attribute, what makes link text good or useless, the target and rel attributes, and why a link is not a butt...