Karatasi ya Maelezo ya MySQL

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Bila Malipo

Rejeleo linalotafutika na linaloweza kuchapishwa la MySQL — hoja, joins, fahirisi, vitendakazi, aina za data na amri za usimamizi. Bila malipo.

Querying

10
SELECT * FROM users;
Select all columns and rows
SELECT id, name FROM users;
Select specific columns
SELECT DISTINCT city FROM users;
Unique values only
WHERE age > 18 AND active = 1
Filter rows by conditions
WHERE name LIKE 'A%'
Pattern match (% = any chars)
WHERE id IN (1, 2, 3)
Match any value in a set
WHERE age BETWEEN 18 AND 30
Inclusive range filter
ORDER BY created_at DESC
Sort descending
LIMIT 10 OFFSET 20
Paginate results
WHERE email IS NULL
Match null values

Joins

8
INNER JOIN orders ON orders.user_id = users.id
Rows matching in both tables
LEFT JOIN orders ON ...
All left rows + matches
RIGHT JOIN orders ON ...
All right rows + matches
CROSS JOIN colors
Cartesian product
SELF JOIN: FROM emp e JOIN emp m ON e.mgr = m.id
Join a table to itself
USING (user_id)
Join on a same-named column
UNION / UNION ALL
Combine result sets
SELECT u.*, o.total FROM users u JOIN orders o
Alias tables for clarity

Aggregation

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COUNT(*)
Count rows
SUM(amount)
Total of a numeric column
AVG(price)
Average value
MIN(price), MAX(price)
Smallest and largest
GROUP BY country
Group rows for aggregation
HAVING COUNT(*) > 5
Filter on aggregated groups
GROUP_CONCAT(name)
Concatenate grouped values
COUNT(DISTINCT city)
Count unique values
ROW_NUMBER() OVER (ORDER BY id)
Window function ranking

Modifying data

8
INSERT INTO users (name) VALUES ('Sam');
Insert a single row
INSERT INTO users (name) VALUES ('A'),('B');
Insert multiple rows
UPDATE users SET active = 1 WHERE id = 5;
Update matching rows
DELETE FROM users WHERE id = 5;
Delete matching rows
TRUNCATE TABLE logs;
Remove all rows quickly
INSERT ... ON DUPLICATE KEY UPDATE
Upsert on a unique key
REPLACE INTO users ...
Delete + insert on conflict
INSERT IGNORE INTO ...
Skip rows that would error

Schema / DDL

9
CREATE TABLE users (id INT PRIMARY KEY);
Create a new table
AUTO_INCREMENT
Auto-numbering column
ALTER TABLE users ADD COLUMN age INT;
Add a column
ALTER TABLE users DROP COLUMN age;
Remove a column
ALTER TABLE users MODIFY name VARCHAR(100);
Change a column type
DROP TABLE IF EXISTS users;
Delete a table
FOREIGN KEY (user_id) REFERENCES users(id)
Reference another table
ON DELETE CASCADE
Cascade deletes to children
CREATE TABLE t2 LIKE t1;
Copy a table structure

Indexes & keys

8
PRIMARY KEY (id)
Unique row identifier
UNIQUE (email)
Enforce unique values
CREATE INDEX idx_name ON users (name);
Speed up lookups on a column
CREATE INDEX idx_ab ON t (a, b);
Composite (multi-column) index
DROP INDEX idx_name ON users;
Remove an index
FULLTEXT (body)
Full-text search index
EXPLAIN SELECT ...;
Show the query plan
SHOW INDEX FROM users;
List indexes on a table

Data types

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INT, BIGINT, TINYINT
Integer types by size
DECIMAL(10, 2)
Exact fixed-point numbers
VARCHAR(255)
Variable-length string
TEXT, LONGTEXT
Large text blobs
DATE, DATETIME, TIMESTAMP
Date and time types
BOOLEAN (TINYINT(1))
True/false stored as 0/1
JSON
Native JSON document column
ENUM('a', 'b')
One of a fixed set of values
UNSIGNED
Non-negative numeric modifier

Type sizes & limits

20
TINYINT
1 byte: -128..127 (0..255 UNSIGNED)
SMALLINT
2 bytes: -32,768..32,767 (0..65,535)
MEDIUMINT
3 bytes: -8.39M..8.39M (0..16.78M)
INT
4 bytes: -2.15B..2.15B (0..4.29B)
BIGINT
8 bytes: ±9.22×10^18 (0..1.84×10^19)
DECIMAL(M, D)
Exact: M up to 65 digits, D up to 30
FLOAT / DOUBLE
4 / 8 bytes approximate floating point
CHAR(M)
Fixed length, 0..255 characters
VARCHAR(M)
0..65,535 bytes (shared 64KB row limit)
TINYTEXT
Up to 255 bytes (~255 chars)
TEXT
Up to 65,535 bytes (64 KB)
MEDIUMTEXT
Up to 16,777,215 bytes (16 MB)
LONGTEXT
Up to 4,294,967,295 bytes (4 GB)
BLOB types
TINY/—/MEDIUM/LONG: 255B..4GB (binary)
JSON
Stored as LONGBLOB, up to ~4 GB
ENUM / SET
ENUM: 65,535 members; SET: 64 members
DATE
1000-01-01 to 9999-12-31 (3 bytes)
DATETIME
1000 to 9999, microseconds (5–8 bytes)
TIMESTAMP
1970-01-01 to 2038-01-19 UTC (4 bytes)
TIME / YEAR
±838:59:59 / 1901..2155

Functions

9
NOW(), CURDATE()
Current datetime / date
DATE_FORMAT(d, '%Y-%m-%d')
Format a date
DATEDIFF(a, b)
Days between two dates
CONCAT(a, ' ', b)
Join strings
COALESCE(a, b, 'n/a')
First non-null value
IFNULL(x, 0)
Replace null with a default
CASE WHEN x > 0 THEN '+' ELSE '-' END
Conditional expression
CAST(x AS CHAR)
Convert a value type
ROUND(x, 2)
Round to decimals

Transactions & admin

9
START TRANSACTION;
Begin a transaction
COMMIT;
Persist the transaction
ROLLBACK;
Undo the transaction
SAVEPOINT sp1;
Set a rollback point
SHOW TABLES;
List tables in the database
DESCRIBE users;
Show a table structure
SHOW PROCESSLIST;
List running connections
GRANT ALL ON db.* TO 'u'@'%';
Grant user privileges
mysqldump -u root db > db.sql
Back up a database (CLI)

Hakuna kipengele kinacholingana na “:q”.

Kuhusu Karatasi ya Maelezo ya MySQL

Karatasi hii ya kumbukumbu ya MySQL hukusanya SQL unayoandika kwa uhalisia kwenye rejea moja inayoweza kutafutwa: querying, joins, aggregation, kubadilisha data, schema na taarifa za DDL, indexes na keys, aina za data pamoja na ukubwa na mipaka yake, functions zilizojengwa ndani, na transactions na amri za usimamizi.

Ni muhimu kama ukumbusho wa sintaksia — umbo hasa la LEFT JOIN, UPSERT au ALTER TABLE — na pia kama sehemu ya kutafuta maelezo ambayo hakuna anayeyakariri, kama vipimo vya integer, mipaka ya VARCHAR na aina gani ya index inafaa query fulani.

Kama kila karatasi ya kumbukumbu kwenye kundi hili la zana ni bure na inafanya kazi upande wa mteja: chuja mistari papo hapo kwa kisanduku cha utafutaji, rukaruka kati ya sehemu kwa orodha ya yaliyomo inayoning'inia, nakili taarifa (statement) yoyote kwa bofyo moja na chapisha ukurasa kwa rejea mezani kwako.

Jinsi ya kutumia Karatasi ya Maelezo ya MySQL

  1. Fungua karatasi na kagua sehemu, kutoka Querying na Joins kupitia Schema / DDL hadi Transactions & admin.
  2. Tafuta neno-msingi kama JOIN, INDEX au GROUP BY kuchuja snippets zote papo hapo.
  3. Ruka kwenye Data types au Type sizes & limits unapohitaji maelezo ya uhifadhi badala ya sintaksia.
  4. Bofya statement au ikoni yake ya kunakili kunakili SQL kwenye clipboard yako.
  5. Tumia Print kwa nakala ya karatasi ya rejea kamili ya MySQL.

Maswali yanayoulizwa mara kwa mara

Sehemu kumi zinazoshughulikia querying, joins, aggregation, kubadilisha data, schema DDL, indexes na keys, aina za data, ukubwa na mipaka ya aina, functions, na transactions pamoja na amri za usimamizi — kila moja kama snippet ya SQL tayari kunakiliwa.

Ndiyo. Sehemu maalum huorodhesha ukubwa na mipaka ya aina — vipimo vya integer na mipaka ya urefu wa string ambayo vinginevyo ungelazimika kutafuta kwenye mwongozo — karibu na sehemu ya aina za data yenyewe.

Ndiyo. Bofya snippet ya SQL au ikoni ya kunakili kwenye mstari wake na itanakiliwa kwenye clipboard yako mara moja.

Vyote viwili. Kisanduku cha utafutaji huchuja kila mstari unapoandika pamoja na hesabu ya ulinganifu ya papo hapo, na kitufe cha Print hutoa toleo safi bila mapambo ya ukurasa.

Ndiyo, ni bure kabisa na hufanya kazi kwenye kivinjari chako bila kuingia (login).
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