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...
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SQL
SQL String Functions
Concatenating, trimming, slicing, replacing and searching text - and which of these functions changes name in every dialect.
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 Date and Time Functions
Current date and time, adding and subtracting intervals, differences between dates, extracting parts, and formatting - the least portable corner of SQ...
SQL
CASE, COALESCE, NULLIF and Conversion Functions
Conditional logic inside a query, NULL substitution, safe division and explicit type conversion - four tools that remove most procedural code from SQL...
SQL
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
Three Valued Logic: TRUE, FALSE and UNKNOWN
SQL conditions return three results, not two. Learn the AND, OR and NOT truth tables, why NOT IN breaks on NULL, and the NULL safe comparison operator...
SQL
COUNT, SUM, AVG, MIN and MAX
The five aggregate functions that collapse many rows into one value, the three forms of COUNT, and what each one does with NULL.
SQL
Aggregates, NULL and Aggregate Expressions
Aggregating an expression rather than a column: weighted totals, conditional counts and the difference between counting rows and counting facts.
SQL
GROUP BY Fundamentals
GROUP BY collapses rows into one row per distinct key. Learn the single rule that governs the select list and how NULLs are grouped.
SQL
HAVING, and WHERE vs HAVING
HAVING filters groups after aggregation, WHERE filters rows before it. Learn when each applies, why using both is usually correct, and which is faster...
SQL
Multi Column Grouping and Grouping Rules
Grouping by several columns, grouping by expressions, and the totals features - ROLLUP, CUBE and GROUPING SETS - that add subtotal rows.