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SQL Notes

SQL from zero to advanced, the cricket way — every concept explained on real IPL data, with a live SQL playground on every topic. Written by Munna Kumar (Code With Munna) — 107 topics in order, each with examples, key points.

Start with What Is SQL & Why Learn It

Intro to SQL

1What Is SQL & Why Learn ItWhat SQL stands for, what problem it solves, and why every data career needs it.
2Database, DBMS & ServerThe three layers behind every query: the data (database), the software that manages it (DBMS) and the machine that runs it (server).
3Types of DatabasesRelational vs NoSQL (document, key-value, graph, column-based) — and why this course focuses on relational.
4Database Structure: Server → TableHow objects are nested — server, database, schema, table — and how tables are physically stored on disk.
5Tables, Rows, Columns & Primary KeysThe anatomy of a table — columns, rows (records), cells — and why every table needs a primary key.
6Data TypesNumeric, string and date/time data types in SQL Server — and how to choose the right one for each column.
7Types of SQL Commands & RoadmapDDL, DML, DQL, DCL and TCL — the five families of SQL commands — and the full course roadmap.

Query Data (SELECT)

8Parts of an SQL QueryStatement, comment, clause, keyword, function, identifier, operator and value — the vocabulary of every query.
9SELECT, FROM & Column AliasesReturn all columns with SELECT *, pick specific columns, add calculated columns and rename them with AS.
10WHERE: Filter RowsKeep only the rows that match a condition — with numbers, text and comparison operators.
11ORDER BY: Sort ResultsSort the result highest-first (DESC) or lowest-first (ASC), and by more than one column.
12GROUP BY & Aggregate FunctionsCombine rows into groups and summarise each group with SUM, COUNT, AVG, MIN and MAX.
13HAVING: Filter GroupsFilter groups after aggregation with HAVING — and understand exactly how it differs from WHERE.
14DISTINCT: Remove DuplicatesReturn each unique value (or combination of values) only once.
15TOP: Limit the RowsReturn only the first N rows with TOP — and its equivalents LIMIT and FETCH FIRST in other databases.
16Execution Order & Putting It TogetherThe real order SQL processes a query — FROM to TOP — plus a full worked example and a SELECT cheat sheet.

Data Definition (DDL)

17What is DDL?Understand the families of SQL commands and how DDL (CREATE, ALTER, DROP) builds and changes the structure of a database.
18Data TypesChoose the right data type for every column — INT, VARCHAR, DECIMAL, DATE and the other common SQL Server types.
19CREATE TABLEBuild a brand-new, empty table with CREATE TABLE — name it, list its columns and types, and add rules.
20Constraints: PRIMARY KEY, NOT NULL, DEFAULTProtect your data with the three essential constraints — unique IDs, required values and automatic defaults.
21Constraints: UNIQUE, CHECK, FOREIGN KEYGo beyond the basics — block duplicate values with UNIQUE, validate values with CHECK and link tables with FOREIGN KEY.
22ALTER TABLE — Add & Drop ColumnsChange an existing table's structure: add a new column with ALTER TABLE … ADD and remove one with DROP COLUMN.
23ALTER COLUMN — Change a Data TypeChange an existing column's data type or size with ALTER COLUMN — and learn how MySQL and PostgreSQL write it differently.
24DROP TABLEDelete a whole table — its structure and all its data — with DROP TABLE, and use it safely.
25Life of a Table & DDL Cheat SheetFollow one table from CREATE to DROP, and keep a one-page DDL cheat sheet plus best practices.

Data Manipulation (DML)

26What is DML?Learn what DML is and how INSERT, UPDATE and DELETE change the data inside your tables.
27INSERT INTO — Add One RowAdd a new row to a table with INSERT INTO … VALUES, using a column list that matches the values.
28INSERT Multiple RowsInsert many rows in a single statement by listing several value lists separated by commas.
29INSERT INTO … SELECTCopy rows from one table into another existing table by feeding a SELECT query into INSERT.
30SELECT INTO — Copy into a New TableCreate and fill a brand-new table from a query in one step with SQL Server's SELECT … INTO.
31UPDATE — Change Existing DataChange values in existing rows with UPDATE … SET … WHERE — one column, many columns, or calculated values.
32DELETE — Remove RowsRemove rows from a table with DELETE FROM … WHERE, and understand why DELETE without WHERE empties the table.
33DELETE vs TRUNCATE vs DROPKnow exactly what DELETE, TRUNCATE and DROP remove, how they differ, and which one to use.
34Safe UPDATE & DELETE HabitsProfessional habits that stop you from accidentally changing or deleting the wrong rows — SELECT first, transactions, backups.

Filtering Data

35WHERE & Building ConditionsUnderstand exactly what WHERE does, how every condition is built (expression + operator + expression), and the five families of WHERE operators.
36Equal (=) & Not Equal (<>, !=)Use = to keep exact matches and <> / != to keep everything except a value.
37Greater / Less Than (> >= < <=)Filter numbers, dates and text by size using >, >=, < and <=, and know exactly when the boundary value is included.
38AND & ORCombine several conditions: AND needs all of them TRUE, OR needs at least one TRUE.
39NOT (Reverse a Condition)Flip a condition with NOT, combine it with IN / BETWEEN / LIKE, and see how it behaves with NULL.
40Precedence & ParenthesesLearn the order SQL evaluates NOT, AND and OR, and use parentheses to make mixed conditions mean what you intend.
41BETWEEN (Range)Filter values inside a range with BETWEEN … AND …, remembering that both ends are included.
42IN & NOT IN (Membership)Match any value in a list with IN, exclude a list with NOT IN, and avoid the NOT IN + NULL trap.
43LIKE & Wildcards (% and _)Search text by pattern with LIKE, using % (any number of characters) and _ (exactly one character).
44IS NULL & IS NOT NULLFind missing values correctly with IS NULL / IS NOT NULL and understand why = NULL never works.
45Filtering Cheat SheetAll WHERE operators on one page, plus a combined practice query that uses several of them together.

JOINs & SET Operators

46Combining Data: JOINs vs SETThe two ways to combine data in SQL — JOINs add columns side by side, SET operators stack rows — plus what a JOIN is, why we join, and the 'No JOIN' baseline.
47INNER JOINReturn only the rows that have a match in both tables — the most common join.
48LEFT JOINKeep every row from the left table and add matching data from the right table (NULL where there is no match).
49RIGHT JOINKeep every row from the right table and add matches from the left — and why most people rewrite it as a LEFT JOIN.
50FULL JOINReturn everything from both tables — matched rows combined, unmatched rows from either side filled with NULLs.
51Anti Joins (Left, Right, Full)Find rows that have NO match in the other table — orphan players, teams without players, and all leftovers.
52CROSS JOINCombine every row of one table with every row of another — the Cartesian product.
53Joining Multiple Tables & Choosing a JoinChain three or more tables with INNER or LEFT JOINs, and a simple decision guide to pick the right join every time.
54SET Operators: Syntax & RulesWhat SET operators are, their syntax, and the five rules every UNION / EXCEPT / INTERSECT query must follow.
55UNION vs UNION ALLStack two result sets — UNION removes duplicate rows, UNION ALL keeps every row and is faster.
56EXCEPT & INTERSECTEXCEPT returns rows in the first query but not the second; INTERSECT returns rows common to both.
57SET Operators: Real Use CasesCombine similar tables with UNION ALL, detect changes (delta) with EXCEPT, and check data completeness between source and warehouse.

Row-Level Functions

58What Are SQL Functions?Understand what a function is, the difference between single-row and multi-row functions, how nesting works, and the SQL functions family.
59String Functions: CONCAT, UPPER, LOWER, TRIM, REPLACEManipulate text: join strings with CONCAT, change case with UPPER/LOWER, clean spaces with TRIM and swap or remove characters with REPLACE.
60String Functions: LEN, LEFT, RIGHT, SUBSTRINGMeasure text with LEN and extract parts of it with LEFT, RIGHT and SUBSTRING (with CHARINDEX for dynamic positions).
61Numeric Functions: ROUND, ABS & MoreRound strike rates with ROUND, remove minus signs with ABS, and learn CEILING, FLOOR, POWER, SQRT and the integer-division trap.
62Date & Time Basics: YEAR, MONTH, DAY, DATEPART, DATENAMELearn the DATE, TIME and DATETIME2 types, get the current time with GETDATE(), and extract parts with YEAR/MONTH/DAY, DATEPART and DATENAME.
63DATETRUNC, EOMONTH & Choosing a Date FunctionReset the lower parts of a date with DATETRUNC to group by month or year, find month-ends with EOMONTH, and choose between DATEPART, DATENAME and DATETRUNC.
64Date Calculations: DATEADD, DATEDIFF, ISDATEAdd or subtract time with DATEADD, measure gaps with DATEDIFF (boundary counting), and validate messy input with ISDATE.
65Formatting & Casting: FORMAT, CONVERT, CASTDisplay dates and numbers your way with FORMAT, change data types with CAST and CONVERT (with date styles), and know which one to pick.
66Understanding NULL: IS NULL, IS NOT NULL, Empty vs BlankLearn what NULL really means, where NULLs come from, how to find them with IS NULL / IS NOT NULL, how they behave in joins, and how NULL differs from '' and ' '.
67NULL Functions: ISNULL, COALESCE, NULLIFReplace NULLs with ISNULL and COALESCE, create NULLs with NULLIF to avoid divide-by-zero, and know when to use each.
68CASE Statement: Searched & SimpleAdd IF / ELSE logic to queries with CASE: syntax, the searched and simple forms, and the three rules — order matters, ELSE is optional, same data type.
69CASE Use Cases: Categorise, Map, Conditional AggregationApply CASE in real reports: multi-condition categories, handling NULLs, custom sorting, and conditional counting/summing inside aggregates.

Aggregation & Window Functions

70Aggregate FunctionsSummarise many rows into one value with COUNT, SUM, AVG, MAX and MIN — and learn exactly how each one treats NULL.
71GROUP BY with AggregatesUse GROUP BY to get one summary row per team or player, and HAVING to filter those groups.
72Window Functions & OVER()Understand what a window function is, how it differs from GROUP BY, the parts of the OVER clause, and the rules for using it.
73PARTITION BY & ORDER BY in OVERSplit the window into one partition per player with PARTITION BY, and make calculations run in order with ORDER BY.
74Window Frames: Running & Rolling TotalsControl exactly which rows a window calculation sees with ROWS BETWEEN, and build running totals, rolling totals and moving averages.
75Aggregate Window FunctionsUse COUNT, SUM, AVG, MIN and MAX with OVER for part-to-whole percentages, NULL-aware averages and row-vs-aggregate comparisons.
76ROW_NUMBER, RANK & DENSE_RANKGive rows a position with ROW_NUMBER, RANK and DENSE_RANK, understand exactly how each handles ties, and pick the right one.
77NTILE, CUME_DIST & PERCENT_RANKSplit rows into equal buckets with NTILE and measure a row's relative position (0 to 1) with CUME_DIST and PERCENT_RANK.
78LAG, LEAD, FIRST_VALUE & LAST_VALUERead a value from the previous, next, first or last row of the window — for match-over-match changes and comparisons without a self-join.
79Window Function Use CasesApply window functions to real problems: top-N per group, top-N with ties, finding and deleting duplicates, month-over-month change, pagination and gaps between dates.

Advanced SQL Techniques

80Why Advanced SQL Techniques?The problem with one giant query, and the six tools SQL gives you to break it into clean, reusable pieces.
81Subqueries: Basics & Result TypesWhat a subquery is, how it runs inside-out, the three result types (scalar, list, table) and subqueries in FROM and SELECT.
82Subqueries in WHERE: IN, NOT IN, ANY, ALLFilter rows against a list returned by a subquery with IN, NOT IN, ANY and ALL — and avoid the NOT IN + NULL trap.
83Correlated Subqueries & EXISTSSubqueries that depend on the outer row, the EXISTS / NOT EXISTS test, and when to use a JOIN instead.
84CTEs: Standalone, Multiple & NestedName a step with WITH … AS, chain several CTEs with commas, and build CTEs on top of earlier CTEs.
85Recursive CTEsA CTE that calls itself: generate number sequences and walk the team_staff reporting hierarchy level by level.
86Views: Saved QueriesCreate views that store a query (not data), use them like tables, and know when to choose a view over a table or CTE.
87CTAS & Temporary TablesSave a query result as a real table with CTAS / SELECT INTO, and use session-only #temp tables for multi-step work.
88Stored ProceduresSave a parameterised SQL program in the database, run it with EXEC, and add IF/ELSE logic and TRY…CATCH error handling.
89Triggers: Automatic ActionsCode that fires by itself on INSERT, UPDATE or DELETE — AFTER, INSTEAD OF and DDL triggers, with a player_log audit example.
90Choosing the Right TechniqueCompare subqueries, CTEs, views, temp tables, CTAS, procedures and triggers side by side, plus a one-page cheat sheet.

Performance Optimization

91What Is an Index?Understand data pages, heaps, full table scans and the B-Tree structure that lets an index find a row in a few hops.
92Clustered vs Non-Clustered IndexLearn how a clustered index physically sorts the table, how a non-clustered index points to rows, and how to create both (plus composite indexes).
93Rowstore vs Columnstore IndexSee how columnstore stores data column by column, how it is built (row groups, segments, compression) and when to use it over rowstore.
94Unique & Filtered IndexesUse a unique index to block duplicates, a filtered index to index only some rows, and learn how to pick the right index type for each job.
95Execution Plans: Scan vs SeekRead an execution plan to see how the database runs your query, and learn the difference between a table scan, an index scan and an index seek.
96Indexing Strategy, Statistics & MaintenancePlan indexes for OLTP vs OLAP, follow the 4-phase indexing strategy, and keep indexes healthy: usage, missing/duplicate indexes, statistics and fragmentation.
97Table PartitioningSplit a huge table into partitions by a key such as match date using a partition function, filegroups, data files and a partition scheme.
98Tips 1–7: Fetching & FilteringThe first 7 of the 30 performance tips: select only what you need, avoid needless DISTINCT/ORDER BY, explore with TOP, and write index-friendly WHERE clauses.
99Tips 8–16: Joining DataNine join tips: pick the right join type, use ANSI syntax, index ON columns, filter and aggregate before joining, avoid OR in joins, watch nested loops and use UNION ALL wisely.
100Tips 17–20: Aggregations & SubqueriesSpeed up heavy aggregations with columnstore and pre-aggregated tables, choose correctly between JOIN, EXISTS and IN, and simplify repeated logic with CTEs.
101Tips 21–30: DDL & IndexingThe last 10 tips: precise data types, sensible lengths, NOT NULL, clustered primary keys, indexed foreign keys, and how to keep indexes lean, fresh and defragmented.

AI & SQL

102Writing Good SQL PromptsThe five parts of a strong prompt, weak vs strong prompts, and where chat and code assistants help with SQL.
103Prompts: Write, Clean & Document SQLPrompts #1, #2, #7 and #8: solve a task, improve readability, format code and add documentation.
104Prompts: Debug, Explain & OptimizePrompts #3, #4, #5 and #6: speed up slow queries, read execution plans, fix errors and understand results.
105Prompts: Review DDL & Generate Test DataPrompts #9 and #10: a five-point design review of your tables, and realistic test INSERTs with valid keys.
106Prompts: Learn, Practice & Interview PrepPrompts #11–#16: build a course, understand and compare concepts, practise interactively, and prepare for interviews and exams.
107The AI + SQL Workflow & Golden RulesAsk → Review → Test → Refine, the 6 golden rules, data safety, and all 16 prompts at a glance.

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